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Re: [PATCH] Implement strlcat [BZ#178]
- From: Paul Eggert <eggert at cs dot ucla dot edu>
- To: Florian Weimer <fweimer at redhat dot com>
- Cc: GNU C Library <libc-alpha at sourceware dot org>
- Date: Thu, 26 Nov 2015 02:34:00 -0800
- Subject: Re: [PATCH] Implement strlcat [BZ#178]
- Authentication-results: sourceware.org; auth=none
- References: <56547472 dot 3010302 at redhat dot com> <5654B1FE dot 5020100 at cs dot ucla dot edu> <5654B796 dot 7070302 at redhat dot com>
Florian Weimer wrote:
I'm attaching the consolidated documentation patch.
Thanks. Attached are three patches fixing the problems I mentioned earlier,
relative to the current glibc master. The first two patches are independent of
strlcpy+strlcat: they switch to less-confusing terminology (e.g., "byte" instead
of "character" when talking about strcpy), and split the enormous "Copying
Strings and Arrays" section into more-manageable subsections while adding advice
about string truncation. The third patch adds strlcpy/strlcat and relies on the
earlier two patches.
I still would rather not add strlcpy+strlcat, but if we're going to add them
they will need decent documentation, and I hope this is good enough.
PS. This time around I noticed that in some cases strlcat is required to not
null-terminate its output, even when there's room for a null byte in the
destination buffer. Eeeuuuw. Do we really want to document that particular
misfeature? Does user code really require it? Perhaps it'd be better to leave
the behavior undefined in that particular case, i.e., to require that strlcat's
first argument be a string if SIZE is nonzero.
>From ea394a3ad72d69d290bc236e29b45e14373d0f28 Mon Sep 17 00:00:00 2001
From: Paul Eggert <eggert@cs.ucla.edu>
Date: Tue, 24 Nov 2015 15:41:51 -0800
Subject: [PATCH 1/3] Consistency about byte vs character in string.texi
* manual/string.texi (String and Array Utilities):
Distinguish more carefully among bytes, multibyte characters,
and wide characters. Use "byte" when talking about C 'char',
to distinguish it more clearly from multibyte characters.
Say "wide character" or "multibyte character" instead of
"character", when a wide or multibyte character is intended.
Similarly for "multibyte character string" versus "string".
Define these terms more carefully.
---
ChangeLog | 12 ++
manual/string.texi | 363 +++++++++++++++++++++++++++--------------------------
2 files changed, 200 insertions(+), 175 deletions(-)
diff --git a/ChangeLog b/ChangeLog
index ceb14b7..f041f67 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,15 @@
+2015-11-26 Paul Eggert <eggert@cs.ucla.edu>
+
+ Consistency about byte vs character in string.texi
+ * manual/string.texi (String and Array Utilities):
+ Distinguish more carefully among bytes, multibyte characters,
+ and wide characters. Use "byte" when talking about C 'char',
+ to distinguish it more clearly from multibyte characters.
+ Say "wide character" or "multibyte character" instead of
+ "character", when a wide or multibyte character is intended.
+ Similarly for "multibyte character string" versus "string".
+ Define these terms more carefully.
+
2015-11-25 Samuel Thibault <samuel.thibault@ens-lyon.org>
* hurd/sigunwind.c (_hurdsig_longjmp_from_handler): Destroy reply port
diff --git a/manual/string.texi b/manual/string.texi
index 5f8a17e..61ff3e2 100644
--- a/manual/string.texi
+++ b/manual/string.texi
@@ -2,7 +2,7 @@
@c %MENU% Utilities for copying and comparing strings and arrays
@chapter String and Array Utilities
-Operations on strings (or arrays of characters) are an important part of
+Operations on strings (null-terminated byte sequences) are an important part of
many programs. @Theglibc{} provides an extensive set of string
utility functions, including functions for copying, concatenating,
comparing, and searching strings. Many of these functions can also
@@ -44,13 +44,13 @@ too.
@cindex string, representation of
This section is a quick summary of string concepts for beginning C
-programmers. It describes how character strings are represented in C
+programmers. It describes how strings are represented in C
and some common pitfalls. If you are already familiar with this
material, you can skip this section.
@cindex string
-@cindex multibyte character string
-A @dfn{string} is an array of @code{char} objects. But string-valued
+A @dfn{string} is a null-terminated array of bytes of type @code{char},
+including the terminating null byte. String-valued
variables are usually declared to be pointers of type @code{char *}.
Such variables do not include space for the text of a string; that has
to be stored somewhere else---in an array variable, a string constant,
@@ -60,66 +60,75 @@ variable. Alternatively you can store a @dfn{null pointer} in the
pointer variable. The null pointer does not point anywhere, so
attempting to reference the string it points to gets an error.
+@cindex multibyte character
+@cindex multibyte character string
@cindex wide character string
-``string'' normally refers to multibyte character strings as opposed to
-wide character strings. Wide character strings are arrays of type
-@code{wchar_t} and as for multibyte character strings usually pointers
-of type @code{wchar_t *} are used.
-
-@cindex null character
+A @dfn{multibyte character} is a sequence of one or more bytes that
+represents a single character using the locale's encoding scheme; a
+null byte always represents the null character. A @dfn{multibyte
+character string} is a string that consists entirely of multibyte
+characters. In contrast, a @dfn{wide character string} is a
+null-terminated sequence of @code{wchar_t} objects and as for strings
+usually pointers of type @code{wchar_t *} are used. @xref{Extended
+Char Intro}.
+
+@cindex null byte
@cindex null wide character
-By convention, a @dfn{null character}, @code{'\0'}, marks the end of a
-multibyte character string and the @dfn{null wide character},
+By convention, the @dfn{null byte}, @code{'\0'},
+marks the end of a string and the @dfn{null wide character},
@code{L'\0'}, marks the end of a wide character string. For example, in
testing to see whether the @code{char *} variable @var{p} points to a
-null character marking the end of a string, you can write
+null byte marking the end of a string, you can write
@code{!*@var{p}} or @code{*@var{p} == '\0'}.
-A null character is quite different conceptually from a null pointer,
+A null byte is quite different conceptually from a null pointer,
although both are represented by the integer @code{0}.
@cindex string literal
-@dfn{String literals} appear in C program source as strings of
-characters between double-quote characters (@samp{"}) where the initial
-double-quote character is immediately preceded by a capital @samp{L}
-(ell) character (as in @code{L"foo"}). In @w{ISO C}, string literals
-can also be formed by @dfn{string concatenation}: @code{"a" "b"} is the
+A @dfn{string literal} appears in C program source as a multibyte
+character string between double-quote characters (@samp{"}). If the
+initial double-quote character is immediately preceded by a capital
+@samp{L} (ell) character (as in @code{L"foo"}), it is a wide string
+literal. Strings can also be formed by @dfn{string concatenation}:
+@code{"a" "b"} is the
same as @code{"ab"}. For wide character strings one can either use
@code{L"a" L"b"} or @code{L"a" "b"}. Modification of string literals is
not allowed by the GNU C compiler, because literals are placed in
read-only storage.
-Character arrays that are declared @code{const} cannot be modified
+Arrays that are declared @code{const} cannot be modified
either. It's generally good style to declare non-modifiable string
pointers to be of type @code{const char *}, since this often allows the
C compiler to detect accidental modifications as well as providing some
amount of documentation about what your program intends to do with the
string.
-The amount of memory allocated for the character array may extend past
-the null character that normally marks the end of the string. In this
-document, the term @dfn{allocated size} is always used to refer to the
-total amount of memory allocated for the string, while the term
-@dfn{length} refers to the number of characters up to (but not
-including) the terminating null character.
+The amount of memory allocated for a byte array may extend past the
+null byte that marks the end of the string that the array contains.
+In this document, the term @dfn{allocated size} is always used to
+refer to the total amount of memory allocated for an array, while the
+term @dfn{length} refers to the number of bytes up to (but not
+including) the terminating null byte. Wide character strings are
+similar, except their sizes and lengths count wide characters, not
+bytes.
@cindex length of string
@cindex allocation size of string
@cindex size of string
@cindex string length
@cindex string allocation
-A notorious source of program bugs is trying to put more characters in a
+A notorious source of program bugs is trying to put more bytes into a
string than fit in its allocated size. When writing code that extends
-strings or moves characters into a pre-allocated array, you should be
+strings or moves bytes into a pre-allocated array, you should be
very careful to keep track of the length of the text and make explicit
checks for overflowing the array. Many of the library functions
@emph{do not} do this for you! Remember also that you need to allocate
-an extra byte to hold the null character that marks the end of the
+an extra byte to hold the null byte that marks the end of the
string.
@cindex single-byte string
@cindex multibyte string
-Originally strings were sequences of bytes where each byte represents a
+Originally strings were sequences of bytes where each byte represented a
single character. This is still true today if the strings are encoded
using a single-byte character encoding. Things are different if the
strings are encoded using a multibyte encoding (for more information on
@@ -130,7 +139,7 @@ has to be aware of this and interpret the byte sequences accordingly.
But since there is no separate interface taking care of these
differences the byte-based string functions are sometimes hard to use.
Since the count parameters of these functions specify bytes a call to
-@code{strncpy} could cut a multibyte character in the middle and put an
+@code{memcpy} could cut a multibyte character in the middle and put an
incomplete (and therefore unusable) byte sequence in the target buffer.
@cindex wide character string
@@ -145,14 +154,14 @@ languages based on syllables still have the problem that more than one
wide character is necessary to complete a logical unit. This is a
higher level problem which the @w{C library} functions are not designed
to solve. But it is at least good that no invalid byte sequences can be
-created. Also, the higher level functions can also much easier operate
-on wide character than on multibyte characters so that a general advise
+created. Also, the higher level functions can also much more easily operate
+on wide characters than on multibyte characters so that a common strategy
is to use wide characters internally whenever text is more than simply
copied.
The remaining of this chapter will discuss the functions for handling
-wide character strings in parallel with the discussion of the multibyte
-character strings since there is almost always an exact equivalent
+wide character strings in parallel with the discussion of
+strings since there is almost always an exact equivalent
available.
@node String/Array Conventions
@@ -160,7 +169,7 @@ available.
This chapter describes both functions that work on arbitrary arrays or
blocks of memory, and functions that are specific to null-terminated
-arrays of characters and wide characters.
+strings and wide strings.
Functions that operate on arbitrary blocks of memory have names
beginning with @samp{mem} and @samp{wmem} (such as @code{memcpy} and
@@ -178,12 +187,12 @@ but arrays of this type.
In contrast, functions that operate specifically on strings and wide
character strings have names beginning with @samp{str} and @samp{wcs}
respectively (such as @code{strcpy} and @code{wcscpy}) and look for a
-null character to terminate the string instead of requiring an explicit
+terminating null byte or null wide character instead of requiring an explicit
size argument to be passed. (Some of these functions accept a specified
-maximum length, but they also check for premature termination with a
-null character.) The array arguments and return values for these
+maximum length, but they also check for premature termination.)
+The array arguments and return values for these
functions have type @code{char *} and @code{wchar_t *} respectively, and
-the array elements are referred to as ``characters'' and ``wide
+the array elements are referred to as ``bytes'' and ``wide
characters''.
In many cases, there are both @samp{mem} and @samp{str}/@samp{wcs}
@@ -202,10 +211,10 @@ Some of the memory and string functions take single characters as
arguments. Since a value of type @code{char} is automatically promoted
into a value of type @code{int} when used as a parameter, the functions
are declared with @code{int} as the type of the parameter in question.
-In case of the wide character function the situation is similarly: the
+In case of the wide character functions the situation is similar: the
parameter type for a single wide character is @code{wint_t} and not
@code{wchar_t}. This would for many implementations not be necessary
-since the @code{wchar_t} is large enough to not be automatically
+since @code{wchar_t} is large enough to not be automatically
promoted, but since the @w{ISO C} standard does not require such a
choice of types the @code{wint_t} type is used.
@@ -222,7 +231,7 @@ This function is declared in the header file @file{string.h}.
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{strlen} function returns the length of the null-terminated
string @var{s} in bytes. (In other words, it returns the offset of the
-terminating null character within the array.)
+terminating null byte within the array.)
For example,
@smallexample
@@ -230,9 +239,9 @@ strlen ("hello, world")
@result{} 12
@end smallexample
-When applied to a character array, the @code{strlen} function returns
+When applied to an array, the @code{strlen} function returns
the length of the string stored there, not its allocated size. You can
-get the allocated size of the character array that holds a string using
+get the allocated size of the array that holds a string using
the @code{sizeof} operator:
@smallexample
@@ -243,7 +252,7 @@ strlen (string)
@result{} 12
@end smallexample
-But beware, this will not work unless @var{string} is the character
+But beware, this will not work unless @var{string} is the
array itself, not a pointer to it. For example:
@smallexample
@@ -292,7 +301,7 @@ The @code{wcslen} function is the wide character equivalent to
wide character string pointed to by @var{ws} (this is also the offset of
the terminating null wide character of @var{ws}).
-Since there are no multi wide character sequences making up one
+Since there are no multi wide character sequences making up one wide
character the return value is not only the offset in the array, it is
also the number of wide characters.
@@ -309,7 +318,8 @@ returns @var{maxlen}. Therefore this function is equivalent to
@code{(strlen (@var{s}) < @var{maxlen} ? strlen (@var{s}) : @var{maxlen})}
but it
is more efficient and works even if the string @var{s} is not
-null-terminated.
+null-terminated so long as @var{maxlen} does not exceed the
+size of @var{s}'s array.
@smallexample
char string[32] = "hello, world";
@@ -358,7 +368,7 @@ destination arrays overlap. For example, if the beginning of the
destination array overlaps the end of the source array, the original
contents of that part of the source array may get overwritten before it
is copied. Even worse, in the case of the string functions, the null
-character marking the end of the string may be lost, and the copy
+byte marking the end of the string may be lost, and the copy
function might get stuck in a loop trashing all the memory allocated to
your program.
@@ -547,8 +557,8 @@ returns the value of @var{block}.
@comment ISO
@deftypefun {char *} strcpy (char *restrict @var{to}, const char *restrict @var{from})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
-This copies characters from the string @var{from} (up to and including
-the terminating null character) into the string @var{to}. Like
+This copies bytes from the string @var{from} (up to and including
+the terminating null byte) into the string @var{to}. Like
@code{memcpy}, this function has undefined results if the strings
overlap. The return value is the value of @var{to}.
@end deftypefun
@@ -568,15 +578,15 @@ the strings overlap. The return value is the value of @var{wto}.
@deftypefun {char *} strncpy (char *restrict @var{to}, const char *restrict @var{from}, size_t @var{size})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function is similar to @code{strcpy} but always copies exactly
-@var{size} characters into @var{to}.
+@var{size} bytes into @var{to}.
If the length of @var{from} is more than @var{size}, then @code{strncpy}
-copies just the first @var{size} characters. Note that in this case
+copies just the first @var{size} bytes. Note that in this case
there is no null terminator written into @var{to}.
If the length of @var{from} is less than @var{size}, then @code{strncpy}
-copies all of @var{from}, followed by enough null characters to add up
-to @var{size} characters in all. This behavior is rarely useful, but it
+copies all of @var{from}, followed by enough null bytes to add up
+to @var{size} bytes in all. This behavior is rarely useful, but it
is specified by the @w{ISO C} standard.
The behavior of @code{strncpy} is undefined if the strings overlap.
@@ -586,7 +596,7 @@ relating to writing past the end of the allocated space for @var{to}.
However, it can also make your program much slower in one common case:
copying a string which is probably small into a potentially large buffer.
In this case, @var{size} may be large, and when it is, @code{strncpy} will
-waste a considerable amount of time copying null characters.
+waste a considerable amount of time copying null bytes.
@end deftypefun
@comment wchar.h
@@ -646,11 +656,11 @@ This function is a GNU extension.
@deftypefun {char *} strndup (const char *@var{s}, size_t @var{size})
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{}}}
This function is similar to @code{strdup} but always copies at most
-@var{size} characters into the newly allocated string.
+@var{size} bytes into the newly allocated string.
If the length of @var{s} is more than @var{size}, then @code{strndup}
-copies just the first @var{size} characters and adds a closing null
-terminator. Otherwise all characters are copied and the string is
+copies just the first @var{size} bytes and adds a closing null
+byte. Otherwise all bytes are copied and the string is
terminated.
This function is different to @code{strncpy} in that it always
@@ -665,7 +675,7 @@ terminates the destination string.
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function is like @code{strcpy}, except that it returns a pointer to
the end of the string @var{to} (that is, the address of the terminating
-null character @code{to + strlen (from)}) rather than the beginning.
+null byte @code{to + strlen (from)}) rather than the beginning.
For example, this program uses @code{stpcpy} to concatenate @samp{foo}
and @samp{bar} to produce @samp{foobar}, which it then prints.
@@ -688,7 +698,7 @@ declared in @file{string.h}.
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function is like @code{wcscpy}, except that it returns a pointer to
the end of the string @var{wto} (that is, the address of the terminating
-null character @code{wto + strlen (wfrom)}) rather than the beginning.
+null wide character @code{wto + wcslen (wfrom)}) rather than the beginning.
This function is not part of ISO or POSIX but was found useful while
developing @theglibc{} itself.
@@ -703,19 +713,19 @@ The behavior of @code{wcpcpy} is undefined if the strings overlap.
@deftypefun {char *} stpncpy (char *restrict @var{to}, const char *restrict @var{from}, size_t @var{size})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function is similar to @code{stpcpy} but copies always exactly
-@var{size} characters into @var{to}.
+@var{size} bytes into @var{to}.
If the length of @var{from} is more than @var{size}, then @code{stpncpy}
-copies just the first @var{size} characters and returns a pointer to the
-character directly following the one which was copied last. Note that in
+copies just the first @var{size} bytes and returns a pointer to the
+byte directly following the one which was copied last. Note that in
this case there is no null terminator written into @var{to}.
If the length of @var{from} is less than @var{size}, then @code{stpncpy}
-copies all of @var{from}, followed by enough null characters to add up
-to @var{size} characters in all. This behavior is rarely useful, but it
+copies all of @var{from}, followed by enough null bytes to add up
+to @var{size} bytes in all. This behavior is rarely useful, but it
is implemented to be useful in contexts where this behavior of the
@code{strncpy} is used. @code{stpncpy} returns a pointer to the
-@emph{first} written null character.
+@emph{first} written null byte.
This function is not part of ISO or POSIX but was found useful while
developing @theglibc{} itself.
@@ -729,7 +739,7 @@ declared in @file{string.h}.
@deftypefun {wchar_t *} wcpncpy (wchar_t *restrict @var{wto}, const wchar_t *restrict @var{wfrom}, size_t @var{size})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function is similar to @code{wcpcpy} but copies always exactly
-@var{wsize} characters into @var{wto}.
+@var{wsize} wide characters into @var{wto}.
If the length of @var{wfrom} is more than @var{size}, then
@code{wcpncpy} copies just the first @var{size} wide characters and
@@ -738,11 +748,11 @@ non-null wide character which was copied last. Note that in this case
there is no null terminator written into @var{wto}.
If the length of @var{wfrom} is less than @var{size}, then @code{wcpncpy}
-copies all of @var{wfrom}, followed by enough null characters to add up
-to @var{size} characters in all. This behavior is rarely useful, but it
+copies all of @var{wfrom}, followed by enough null wide characters to add up
+to @var{size} wide characters in all. This behavior is rarely useful, but it
is implemented to be useful in contexts where this behavior of the
@code{wcsncpy} is used. @code{wcpncpy} returns a pointer to the
-@emph{first} written null character.
+@emph{first} written null wide character.
This function is not part of ISO or POSIX but was found useful while
developing @theglibc{} itself.
@@ -800,9 +810,9 @@ parameter list in a function call.
@deftypefun {char *} strcat (char *restrict @var{to}, const char *restrict @var{from})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{strcat} function is similar to @code{strcpy}, except that the
-characters from @var{from} are concatenated or appended to the end of
-@var{to}, instead of overwriting it. That is, the first character from
-@var{from} overwrites the null character marking the end of @var{to}.
+bytes from @var{from} are concatenated or appended to the end of
+@var{to}, instead of overwriting it. That is, the first byte from
+@var{from} overwrites the null byte marking the end of @var{to}.
An equivalent definition for @code{strcat} would be:
@@ -823,9 +833,9 @@ This function has undefined results if the strings overlap.
@deftypefun {wchar_t *} wcscat (wchar_t *restrict @var{wto}, const wchar_t *restrict @var{wfrom})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{wcscat} function is similar to @code{wcscpy}, except that the
-characters from @var{wfrom} are concatenated or appended to the end of
-@var{wto}, instead of overwriting it. That is, the first character from
-@var{wfrom} overwrites the null character marking the end of @var{wto}.
+wide characters from @var{wfrom} are concatenated or appended to the end of
+@var{wto}, instead of overwriting it. That is, the first wide character from
+@var{wfrom} overwrites the null wide character marking the end of @var{wto}.
An equivalent definition for @code{wcscat} would be:
@@ -972,8 +982,8 @@ is almost always unnecessary to use @code{strcat}.
@deftypefun {char *} strncat (char *restrict @var{to}, const char *restrict @var{from}, size_t @var{size})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function is like @code{strcat} except that not more than @var{size}
-characters from @var{from} are appended to the end of @var{to}. A
-single null character is also always appended to @var{to}, so the total
+bytes from @var{from} are appended to the end of @var{to}. A
+single null byte is also always appended to @var{to}, so the total
allocated size of @var{to} must be at least @code{@var{size} + 1} bytes
longer than its initial length.
@@ -999,10 +1009,11 @@ The behavior of @code{strncat} is undefined if the strings overlap.
@deftypefun {wchar_t *} wcsncat (wchar_t *restrict @var{wto}, const wchar_t *restrict @var{wfrom}, size_t @var{size})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function is like @code{wcscat} except that not more than @var{size}
-characters from @var{from} are appended to the end of @var{to}. A
-single null character is also always appended to @var{to}, so the total
-allocated size of @var{to} must be at least @code{@var{size} + 1} bytes
-longer than its initial length.
+wide characters from @var{from} are appended to the end of @var{to}. A
+single null wide character is also always appended to @var{to}, so the total
+allocated size of @var{to} must be at least @code{wcsnlen
+(@var{wfrom}, @var{size}) + 1} wide characters longer than its initial
+length.
The @code{wcsncat} function could be implemented like this:
@@ -1025,7 +1036,7 @@ The behavior of @code{wcsncat} is undefined if the strings overlap.
Here is an example showing the use of @code{strncpy} and @code{strncat}
(the wide character version is equivalent). Notice how, in the call to
@code{strncat}, the @var{size} parameter is computed to avoid
-overflowing the character array @code{buffer}.
+overflowing the array @code{buffer}.
@smallexample
@include strncat.c.texi
@@ -1073,7 +1084,7 @@ operations. @xref{Searching and Sorting}, for an example of this.
Unlike most comparison operations in C, the string comparison functions
return a nonzero value if the strings are @emph{not} equivalent rather
than if they are. The sign of the value indicates the relative ordering
-of the first characters in the strings that are not equivalent: a
+of the first part of the strings that are not equivalent: a
negative value indicates that the first string is ``less'' than the
second, while a positive value indicates that the first string is
``greater''.
@@ -1106,7 +1117,7 @@ The function @code{wmemcmp} compares the @var{size} wide characters
beginning at @var{a1} against the @var{size} wide characters beginning
at @var{a2}. The value returned is smaller than or larger than zero
depending on whether the first differing wide character is @var{a1} is
-smaller or larger than the corresponding character in @var{a2}.
+smaller or larger than the corresponding wide character in @var{a2}.
If the contents of the two blocks are equal, @code{wmemcmp} returns
@code{0}.
@@ -1126,7 +1137,7 @@ at a time and this number of bytes is system dependent.
You should also be careful about using @code{memcmp} to compare objects
that can contain ``holes'', such as the padding inserted into structure
objects to enforce alignment requirements, extra space at the end of
-unions, and extra characters at the ends of strings whose length is less
+unions, and extra bytes at the ends of strings whose length is less
than their allocated size. The contents of these ``holes'' are
indeterminate and may cause strange behavior when performing byte-wise
comparisons. For more predictable results, perform an explicit
@@ -1157,7 +1168,7 @@ you are better off writing a specialized comparison function to compare
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{strcmp} function compares the string @var{s1} against
@var{s2}, returning a value that has the same sign as the difference
-between the first differing pair of characters (interpreted as
+between the first differing pair of bytes (interpreted as
@code{unsigned char} objects, then promoted to @code{int}).
If the two strings are equal, @code{strcmp} returns @code{0}.
@@ -1179,7 +1190,7 @@ strings are written in into account. To get that one has to use
The @code{wcscmp} function compares the wide character string @var{ws1}
against @var{ws2}. The value returned is smaller than or larger than zero
depending on whether the first differing wide character is @var{ws1} is
-smaller or larger than the corresponding character in @var{ws2}.
+smaller or larger than the corresponding wide character in @var{ws2}.
If the two strings are equal, @code{wcscmp} returns @code{0}.
@@ -1201,7 +1212,8 @@ strings are written in into account. To get that one has to use
@c There are some asm implementations too, for which the single-read
@c from locale TLS pointers also applies.
This function is like @code{strcmp}, except that differences in case are
-ignored. How uppercase and lowercase characters are related is
+ignored, and its arguments must be multibyte character strings.
+How uppercase and lowercase characters are related is
determined by the currently selected locale. In the standard @code{"C"}
locale the characters @"A and @"a do not match but in a locale which
regards these characters as parts of the alphabet they do match.
@@ -1231,8 +1243,8 @@ regards these characters as parts of the alphabet they do match.
@deftypefun int strncmp (const char *@var{s1}, const char *@var{s2}, size_t @var{size})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This function is the similar to @code{strcmp}, except that no more than
-@var{size} characters are compared. In other words, if the two
-strings are the same in their first @var{size} characters, the
+@var{size} bytes are compared. In other words, if the two
+strings are the same in their first @var{size} bytes, the
return value is zero.
@end deftypefun
@@ -1251,7 +1263,9 @@ return value is zero.
@deftypefun int strncasecmp (const char *@var{s1}, const char *@var{s2}, size_t @var{n})
@safety{@prelim{}@mtsafe{@mtslocale{}}@assafe{}@acsafe{}}
This function is like @code{strncmp}, except that differences in case
-are ignored. Like @code{strcasecmp}, it is locale dependent how
+are ignored, and the compared parts of the arguments should consist of
+valid multibyte characters.
+Like @code{strcasecmp}, it is locale dependent how
uppercase and lowercase characters are related.
@noindent
@@ -1283,13 +1297,13 @@ strcmp ("hello", "hello")
strcmp ("hello", "Hello")
@result{} 32 /* @r{Comparisons are case-sensitive.} */
strcmp ("hello", "world")
- @result{} -15 /* @r{The character @code{'h'} comes before @code{'w'}.} */
+ @result{} -15 /* @r{The byte @code{'h'} comes before @code{'w'}.} */
strcmp ("hello", "hello, world")
- @result{} -44 /* @r{Comparing a null character against a comma.} */
+ @result{} -44 /* @r{Comparing a null byte against a comma.} */
strncmp ("hello", "hello, world", 5)
- @result{} 0 /* @r{The initial 5 characters are the same.} */
+ @result{} 0 /* @r{The initial 5 bytes are the same.} */
strncmp ("hello, world", "hello, stupid world!!!", 5)
- @result{} 0 /* @r{The initial 5 characters are the same.} */
+ @result{} 0 /* @r{The initial 5 bytes are the same.} */
@end smallexample
@comment string.h
@@ -1303,7 +1317,7 @@ return value follows the same conventions as found in the
@code{strcmp} function. In fact, if @var{s1} and @var{s2} contain no
digits, @code{strverscmp} behaves like @code{strcmp}.
-Basically, we compare strings normally (character by character), until
+Basically, we compare strings normally (byte by byte), until
we find a digit in each string - then we enter a special comparison
mode, where each sequence of digits is taken as a whole. If we reach the
end of these two parts without noticing a difference, we return to the
@@ -1378,7 +1392,8 @@ the same as that for @code{strcmp}. Similarly, @code{wcscoll} and
@code{wcscmp} are the same in this situation.
Effectively, the way these functions work is by applying a mapping to
-transform the characters in a string to a byte sequence that represents
+transform the characters in a multibyte character string to a byte
+sequence that represents
the string's position in the collating sequence of the current locale.
Comparing two such byte sequences in a simple fashion is equivalent to
comparing the strings with the locale's collating sequence.
@@ -1399,7 +1414,7 @@ transformed strings with @code{strcmp} or @code{wcscmp}.
@c LC_COLLATE data pointer.
The @code{strcoll} function is similar to @code{strcmp} but uses the
collating sequence of the current locale for collation (the
-@code{LC_COLLATE} locale).
+@code{LC_COLLATE} locale). The arguments are multibyte character strings.
@end deftypefun
@comment wchar.h
@@ -1448,10 +1463,11 @@ sort_strings (char **array, int nstrings)
@comment ISO
@deftypefun size_t strxfrm (char *restrict @var{to}, const char *restrict @var{from}, size_t @var{size})
@safety{@prelim{}@mtsafe{@mtslocale{}}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{}}}
-The function @code{strxfrm} transforms the string @var{from} using the
+The function @code{strxfrm} transforms the multibyte character string
+@var{from} using the
collation transformation determined by the locale currently selected for
collation, and stores the transformed string in the array @var{to}. Up
-to @var{size} characters (including a terminating null character) are
+to @var{size} bytes (including a terminating null byte) are
stored.
The behavior is undefined if the strings @var{to} and @var{from}
@@ -1467,8 +1483,8 @@ string, call @code{strxfrm} again with a bigger output array.
The transformed string may be longer than the original string, and it
may also be shorter.
-If @var{size} is zero, no characters are stored in @var{to}. In this
-case, @code{strxfrm} simply returns the number of characters that would
+If @var{size} is zero, no bytes are stored in @var{to}. In this
+case, @code{strxfrm} simply returns the number of bytes that would
be the length of the transformed string. This is useful for determining
what size the allocated array should be. It does not matter what
@var{to} is if @var{size} is zero; @var{to} may even be a null pointer.
@@ -1482,7 +1498,7 @@ The function @code{wcsxfrm} transforms wide character string @var{wfrom}
using the collation transformation determined by the locale currently
selected for collation, and stores the transformed string in the array
@var{wto}. Up to @var{size} wide characters (including a terminating null
-character) are stored.
+wide character) are stored.
The behavior is undefined if the strings @var{wto} and @var{wfrom}
overlap; see @ref{Copying and Concatenation}.
@@ -1498,7 +1514,7 @@ was stored. To get the whole transformed wide character string, call
The transformed wide character string may be longer than the original
wide character string, and it may also be shorter.
-If @var{size} is zero, no characters are stored in @var{to}. In this
+If @var{size} is zero, no wide characters are stored in @var{to}. In this
case, @code{wcsxfrm} simply returns the number of wide characters that
would be the length of the transformed wide character string. This is
useful for determining what size the allocated array should be (remember
@@ -1558,7 +1574,7 @@ sort_strings_fast (char **array, int nstrings)
if (transformed_length >= length)
@{
/* @r{Allocate the needed space. +1 for terminating}
- @r{@code{NUL} character.} */
+ @r{@code{'\0'} byte.} */
transformed = (char *) xrealloc (transformed,
transformed_length + 1);
@@ -1602,7 +1618,7 @@ sort_strings_fast (wchar_t **array, int nstrings)
if (transformed_length >= length)
@{
/* @r{Allocate the needed space. +1 for terminating}
- @r{@code{NUL} character.} */
+ @r{@code{L'\0'} wide character.} */
transformed = (wchar_t *) xrealloc (transformed,
(transformed_length + 1)
* sizeof (wchar_t));
@@ -1700,10 +1716,10 @@ This function is a GNU extension.
@comment ISO
@deftypefun {char *} strchr (const char *@var{string}, int @var{c})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
-The @code{strchr} function finds the first occurrence of the character
+The @code{strchr} function finds the first occurrence of the byte
@var{c} (converted to a @code{char}) in the null-terminated string
beginning at @var{string}. The return value is a pointer to the located
-character, or a null pointer if no match was found.
+byte, or a null pointer if no match was found.
For example,
@smallexample
@@ -1713,12 +1729,12 @@ strchr ("hello, world", '?')
@result{} NULL
@end smallexample
-The terminating null character is considered to be part of the string,
+The terminating null byte is considered to be part of the string,
so you can use this function get a pointer to the end of a string by
-specifying a null character as the value of the @var{c} argument.
+specifying zero as the value of the @var{c} argument.
When @code{strchr} returns a null pointer, it does not let you know
-the position of the terminating null character it has found. If you
+the position of the terminating null byte it has found. If you
need that information, it is better (but less portable) to use
@code{strchrnul} than to search for it a second time.
@end deftypefun
@@ -1732,9 +1748,9 @@ character @var{wc} in the null-terminated wide character string
beginning at @var{wstring}. The return value is a pointer to the
located wide character, or a null pointer if no match was found.
-The terminating null character is considered to be part of the wide
+The terminating null wide character is considered to be part of the wide
character string, so you can use this function get a pointer to the end
-of a wide character string by specifying a null wude character as the
+of a wide character string by specifying a null wide character as the
value of the @var{wc} argument. It would be better (but less portable)
to use @code{wcschrnul} in this case, though.
@end deftypefun
@@ -1744,8 +1760,8 @@ to use @code{wcschrnul} in this case, though.
@deftypefun {char *} strchrnul (const char *@var{string}, int @var{c})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@code{strchrnul} is the same as @code{strchr} except that if it does
-not find the character, it returns a pointer to string's terminating
-null character rather than a null pointer.
+not find the byte, it returns a pointer to string's terminating
+null byte rather than a null pointer.
This function is a GNU extension.
@end deftypefun
@@ -1762,7 +1778,7 @@ This function is a GNU extension.
@end deftypefun
One useful, but unusual, use of the @code{strchr}
-function is when one wants to have a pointer pointing to the NUL byte
+function is when one wants to have a pointer pointing to the null byte
terminating a string. This is often written in this way:
@smallexample
@@ -1779,7 +1795,7 @@ is this:
@end smallexample
There is no restriction on the second parameter of @code{strchr} so it
-could very well also be the NUL character. Those readers thinking very
+could very well also be zero. Those readers thinking very
hard about this might now point out that the @code{strchr} function is
more expensive than the @code{strlen} function since we have two abort
criteria. This is right. But in @theglibc{} the implementation of
@@ -1815,9 +1831,9 @@ from the front).
@deftypefun {char *} strstr (const char *@var{haystack}, const char *@var{needle})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This is like @code{strchr}, except that it searches @var{haystack} for a
-substring @var{needle} rather than just a single character. It
+substring @var{needle} rather than just a single byte. It
returns a pointer into the string @var{haystack} that is the first
-character of the substring, or a null pointer if no match was found. If
+byte of the substring, or a null pointer if no match was found. If
@var{needle} is an empty string, the function returns @var{haystack}.
For example,
@@ -1858,7 +1874,8 @@ name originally used in the X/Open Portability Guide before the
@c object independently.
This is like @code{strstr}, except that it ignores case in searching for
the substring. Like @code{strcasecmp}, it is locale dependent how
-uppercase and lowercase characters are related.
+uppercase and lowercase characters are related, and arguments are
+multibyte character strings.
For example,
@@ -1888,9 +1905,9 @@ This function is a GNU extension.
@deftypefun size_t strspn (const char *@var{string}, const char *@var{skipset})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{strspn} (``string span'') function returns the length of the
-initial substring of @var{string} that consists entirely of characters that
+initial substring of @var{string} that consists entirely of bytes that
are members of the set specified by the string @var{skipset}. The order
-of the characters in @var{skipset} is not important.
+of the bytes in @var{skipset} is not important.
For example,
@smallexample
@@ -1898,9 +1915,8 @@ strspn ("hello, world", "abcdefghijklmnopqrstuvwxyz")
@result{} 5
@end smallexample
-Note that ``character'' is here used in the sense of byte. In a string
-using a multibyte character encoding (abstract) character consisting of
-more than one byte are not treated as an entity. Each byte is treated
+In a string using a multibyte character encoding, characters consisting of
+more than one byte are not treated as single entities. Each byte is treated
separately. The function is not locale-dependent.
@end deftypefun
@@ -1920,9 +1936,9 @@ important.
@deftypefun size_t strcspn (const char *@var{string}, const char *@var{stopset})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{strcspn} (``string complement span'') function returns the length
-of the initial substring of @var{string} that consists entirely of characters
+of the initial substring of @var{string} that consists entirely of bytes
that are @emph{not} members of the set specified by the string @var{stopset}.
-(In other words, it returns the offset of the first character in @var{string}
+(In other words, it returns the offset of the first byte in @var{string}
that is a member of the set @var{stopset}.)
For example,
@@ -1931,9 +1947,8 @@ strcspn ("hello, world", " \t\n,.;!?")
@result{} 5
@end smallexample
-Note that ``character'' is here used in the sense of byte. In a string
-using a multibyte character encoding (abstract) character consisting of
-more than one byte are not treated as an entity. Each byte is treated
+In a string using a multibyte character encoding, characters consisting of
+more than one byte are not treated as a single entities. Each byte is treated
separately. The function is not locale-dependent.
@end deftypefun
@@ -1945,7 +1960,7 @@ The @code{wcscspn} (``wide character string complement span'') function
returns the length of the initial substring of @var{wstring} that
consists entirely of wide characters that are @emph{not} members of the
set specified by the string @var{stopset}. (In other words, it returns
-the offset of the first character in @var{string} that is a member of
+the offset of the first wide character in @var{string} that is a member of
the set @var{stopset}.)
@end deftypefun
@@ -1954,10 +1969,10 @@ the set @var{stopset}.)
@deftypefun {char *} strpbrk (const char *@var{string}, const char *@var{stopset})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{strpbrk} (``string pointer break'') function is related to
-@code{strcspn}, except that it returns a pointer to the first character
+@code{strcspn}, except that it returns a pointer to the first byte
in @var{string} that is a member of the set @var{stopset} instead of the
length of the initial substring. It returns a null pointer if no such
-character from @var{stopset} is found.
+byte from @var{stopset} is found.
@c @group Invalid outside the example.
For example,
@@ -1968,9 +1983,8 @@ strpbrk ("hello, world", " \t\n,.;!?")
@end smallexample
@c @end group
-Note that ``character'' is here used in the sense of byte. In a string
-using a multibyte character encoding (abstract) character consisting of
-more than one byte are not treated as an entity. Each byte is treated
+In a string using a multibyte character encoding, characters consisting of
+more than one byte are not treated as single entities. Each byte is treated
separately. The function is not locale-dependent.
@end deftypefun
@@ -1982,7 +1996,7 @@ The @code{wcspbrk} (``wide character string pointer break'') function is
related to @code{wcscspn}, except that it returns a pointer to the first
wide character in @var{wstring} that is a member of the set
@var{stopset} instead of the length of the initial substring. It
-returns a null pointer if no such character from @var{stopset} is found.
+returns a null pointer if no such wide character from @var{stopset} is found.
@end deftypefun
@@ -2037,26 +2051,25 @@ It is guaranteed that no other library function ever calls @code{strtok}
behind your back (which would mess up this internal state information).
The @var{delimiters} argument is a string that specifies a set of delimiters
-that may surround the token being extracted. All the initial characters
-that are members of this set are discarded. The first character that is
+that may surround the token being extracted. All the initial bytes
+that are members of this set are discarded. The first byte that is
@emph{not} a member of this set of delimiters marks the beginning of the
next token. The end of the token is found by looking for the next
-character that is a member of the delimiter set. This character in the
-original string @var{newstring} is overwritten by a null character, and the
+byte that is a member of the delimiter set. This byte in the
+original string @var{newstring} is overwritten by a null byte, and the
pointer to the beginning of the token in @var{newstring} is returned.
On the next call to @code{strtok}, the searching begins at the next
-character beyond the one that marked the end of the previous token.
+byte beyond the one that marked the end of the previous token.
Note that the set of delimiters @var{delimiters} do not have to be the
same on every call in a series of calls to @code{strtok}.
If the end of the string @var{newstring} is reached, or if the remainder of
-string consists only of delimiter characters, @code{strtok} returns
+string consists only of delimiter bytes, @code{strtok} returns
a null pointer.
-Note that ``character'' is here used in the sense of byte. In a string
-using a multibyte character encoding (abstract) character consisting of
-more than one byte are not treated as an entity. Each byte is treated
+In a string using a multibyte character encoding, characters consisting of
+more than one byte are not treated as single entities. Each byte is treated
separately. The function is not locale-dependent.
@end deftypefun
@@ -2148,8 +2161,8 @@ token = strtok (NULL, delimiters); /* token => NULL */
@end smallexample
@Theglibc{} contains two more functions for tokenizing a string
-which overcome the limitation of non-reentrancy. They are only
-available for multibyte character strings.
+which overcome the limitation of non-reentrancy. They are not
+available available for wide character strings.
@comment string.h
@comment POSIX
@@ -2181,8 +2194,8 @@ and updating @var{string_ptr} to point to the beginning of the next
token.
One difference between @code{strsep} and @code{strtok_r} is that if the
-input string contains more than one character from @var{delimiter} in a
-row @code{strsep} returns an empty string for each pair of characters
+input string contains more than one byte from @var{delimiter} in a
+row @code{strsep} returns an empty string for each pair of bytes
from @var{delimiter}. This means that a program normally should test
for @code{strsep} returning an empty string before processing it.
@@ -2262,8 +2275,8 @@ on different systems.
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This is the standard XPG defined @code{basename}. It is similar in
spirit to the GNU version, but may modify the @var{path} by removing
-trailing '/' characters. If the @var{path} is made up entirely of '/'
-characters, then "/" will be returned. Also, if @var{path} is
+trailing '/' bytes. If the @var{path} is made up entirely of '/'
+bytes, then "/" will be returned. Also, if @var{path} is
@code{NULL} or an empty string, then "." is returned. The prototype for
the XPG version can be found in @file{libgen.h}.
@@ -2299,7 +2312,7 @@ main (int argc, char *argv[])
The @code{dirname} function is the compliment to the XPG version of
@code{basename}. It returns the parent directory of the file specified
by @var{path}. If @var{path} is @code{NULL}, an empty string, or
-contains no '/' characters, then "." is returned. The prototype for this
+contains no '/' bytes, then "." is returned. The prototype for this
function can be found in @file{libgen.h}.
@end deftypefun
@@ -2379,7 +2392,7 @@ that described in @xref{Cryptographic Functions}.
To store or transfer binary data in environments which only support text
one has to encode the binary data by mapping the input bytes to
-characters in the range allowed for storing or transferring. SVID
+bytes in the range allowed for storing or transferring. SVID
systems (and nowadays XPG compliant systems) provide minimal support for
this task.
@@ -2387,8 +2400,8 @@ this task.
@comment XPG
@deftypefun {char *} l64a (long int @var{n})
@safety{@prelim{}@mtunsafe{@mtasurace{:l64a}}@asunsafe{}@acsafe{}}
-This function encodes a 32-bit input value using characters from the
-basic character set. It returns a pointer to a 7 character buffer which
+This function encodes a 32-bit input value using bytes from the
+basic character set. It returns a pointer to a 7 byte buffer which
contains an encoded version of @var{n}. To encode a series of bytes the
user must copy the returned string to a destination buffer. It returns
the empty string if @var{n} is zero, which is somewhat bizarre but
@@ -2464,17 +2477,17 @@ used.
@deftypefun {long int} a64l (const char *@var{string})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The parameter @var{string} should contain a string which was produced by
-a call to @code{l64a}. The function processes at least 6 characters of
-this string, and decodes the characters it finds according to the table
-below. It stops decoding when it finds a character not in the table,
+a call to @code{l64a}. The function processes at least 6 bytes of
+this string, and decodes the bytes it finds according to the table
+below. It stops decoding when it finds a byte not in the table,
rather like @code{atoi}; if you have a buffer which has been broken into
-lines, you must be careful to skip over the end-of-line characters.
+lines, you must be careful to skip over the end-of-line bytes.
The decoded number is returned as a @code{long int} value.
@end deftypefun
The @code{l64a} and @code{a64l} functions use a base 64 encoding, in
-which each character of an encoded string represents six bits of an
+which each byte of an encoded string represents six bits of an
input word. These symbols are used for the base 64 digits:
@multitable {xxxxx} {xxx} {xxx} {xxx} {xxx} {xxx} {xxx} {xxx} {xxx}
@@ -2505,16 +2518,16 @@ Generally, it is better to use one of these encodings.
@section Argz and Envz Vectors
@cindex argz vectors (string vectors)
-@cindex string vectors, null-character separated
-@cindex argument vectors, null-character separated
+@cindex string vectors, null-byte separated
+@cindex argument vectors, null-byte separated
@dfn{argz vectors} are vectors of strings in a contiguous block of
-memory, each element separated from its neighbors by null-characters
+memory, each element separated from its neighbors by null bytes
(@code{'\0'}).
@cindex envz vectors (environment vectors)
-@cindex environment vectors, null-character separated
+@cindex environment vectors, null-byte separated
@dfn{Envz vectors} are an extension of argz vectors where each element is a
-name-value pair, separated by a @code{'='} character (as in a Unix
+name-value pair, separated by a @code{'='} byte (as in a Unix
environment).
@menu
@@ -2563,7 +2576,7 @@ the same elements, which is returned in @var{argz} and @var{argz_len}.
The @code{argz_create_sep} function converts the null-terminated string
@var{string} into an argz vector (returned in @var{argz} and
@var{argz_len}) by splitting it into elements at every occurrence of the
-character @var{sep}.
+byte @var{sep}.
@end deftypefun
@comment argz.h
@@ -2597,7 +2610,7 @@ still active. This function is useful for passing the elements in
@deftypefun {void} argz_stringify (char *@var{argz}, size_t @var{len}, int @var{sep})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{argz_stringify} converts @var{argz} into a normal string with
-the elements separated by the character @var{sep}, by replacing each
+the elements separated by the byte @var{sep}, by replacing each
@code{'\0'} inside @var{argz} (except the last one, which terminates the
string) with @var{sep}. This is handy for printing @var{argz} in a
readable manner.
@@ -2619,7 +2632,7 @@ argz vector @code{*@var{argz}}, and updates @code{*@var{argz}} and
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{}}}
The @code{argz_add_sep} function is similar to @code{argz_add}, but
@var{str} is split into separate elements in the result at occurrences of
-the character @var{delim}. This is useful, for instance, for
+the byte @var{delim}. This is useful, for instance, for
adding the components of a Unix search path to an argz vector, by using
a value of @code{':'} for @var{delim}.
@end deftypefun
@@ -2714,11 +2727,11 @@ of each element; as such, argz functions can also be used on them, where it
makes sense.
Each element in an envz vector is a name-value pair, separated by a @code{'='}
-character; if multiple @code{'='} characters are present in an element, those
+byte; if multiple @code{'='} bytes are present in an element, those
after the first are considered part of the value, and treated like all other
-non-@code{'\0'} characters.
+non-@code{'\0'} bytes.
-If @emph{no} @code{'='} characters are present in an element, that element is
+If @emph{no} @code{'='} bytes are present in an element, that element is
considered the name of a ``null'' entry, as distinct from an entry with an
empty value: @code{envz_get} will return @code{0} if given the name of null
entry, whereas an entry with an empty value would result in a value of
@@ -2738,7 +2751,7 @@ These functions are declared in the standard include file @file{envz.h}.
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{envz_entry} function finds the entry in @var{envz} with the name
@var{name}, and returns a pointer to the whole entry---that is, the argz
-element which begins with @var{name} followed by a @code{'='} character. If
+element which begins with @var{name} followed by a @code{'='} byte. If
there is no entry with that name, @code{0} is returned.
@end deftypefun
--
2.1.0
>From ec8937afe2f2a84229895dedc1b41ab0248920f2 Mon Sep 17 00:00:00 2001
From: Paul Eggert <eggert@cs.ucla.edu>
Date: Thu, 26 Nov 2015 01:13:19 -0800
Subject: [PATCH 2/3] Split large string section; add truncation advice
* manual/string.texi (Copying Strings and Arrays): Split into
three sections Copying Strings and Arrays, Concatenating Strings,
and Truncating Strings, as this section was way too long. All
cross-referenced changed. Add advice about string-truncation
functions.
---
ChangeLog | 7 +
manual/lang.texi | 2 +-
manual/locale.texi | 4 +-
manual/memory.texi | 2 +-
manual/stdio.texi | 2 +-
manual/string.texi | 420 +++++++++++++++++++++++++++++++----------------------
6 files changed, 260 insertions(+), 177 deletions(-)
diff --git a/ChangeLog b/ChangeLog
index f041f67..e4f86e9 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,12 @@
2015-11-26 Paul Eggert <eggert@cs.ucla.edu>
+ Split large string section; add truncation advice
+ * manual/string.texi (Copying Strings and Arrays): Split into
+ three sections Copying Strings and Arrays, Concatenating Strings,
+ and Truncating Strings, as this section was way too long. All
+ cross-referenced changed. Add advice about string-truncation
+ functions.
+
Consistency about byte vs character in string.texi
* manual/string.texi (String and Array Utilities):
Distinguish more carefully among bytes, multibyte characters,
diff --git a/manual/lang.texi b/manual/lang.texi
index 28b21cb..7f8a368 100644
--- a/manual/lang.texi
+++ b/manual/lang.texi
@@ -582,7 +582,7 @@ type that exists only for this purpose.
This is an unsigned integer type used to represent the sizes of objects.
The result of the @code{sizeof} operator is of this type, and functions
such as @code{malloc} (@pxref{Unconstrained Allocation}) and
-@code{memcpy} (@pxref{Copying and Concatenation}) accept arguments of
+@code{memcpy} (@pxref{Copying Strings and Arrays}) accept arguments of
this type to specify object sizes. On systems using @theglibc{}, this
will be @w{@code{unsigned int}} or @w{@code{unsigned long int}}.
diff --git a/manual/locale.texi b/manual/locale.texi
index ee1c3a1..1828500 100644
--- a/manual/locale.texi
+++ b/manual/locale.texi
@@ -374,8 +374,8 @@ a null pointer as the @var{locale} argument. In this case,
currently selected for category @var{category}.
The string returned by @code{setlocale} can be overwritten by subsequent
-calls, so you should make a copy of the string (@pxref{Copying and
-Concatenation}) if you want to save it past any further calls to
+calls, so you should make a copy of the string (@pxref{Copying Strings
+and Arrays}) if you want to save it past any further calls to
@code{setlocale}. (The standard library is guaranteed never to call
@code{setlocale} itself.)
diff --git a/manual/memory.texi b/manual/memory.texi
index cea2cd7..700555e 100644
--- a/manual/memory.texi
+++ b/manual/memory.texi
@@ -547,7 +547,7 @@ The contents of the block are undefined; you must initialize it yourself
Normally you would cast the value as a pointer to the kind of object
that you want to store in the block. Here we show an example of doing
so, and of initializing the space with zeros using the library function
-@code{memset} (@pxref{Copying and Concatenation}):
+@code{memset} (@pxref{Copying Strings and Arrays}):
@smallexample
struct foo *ptr;
diff --git a/manual/stdio.texi b/manual/stdio.texi
index c0753b1..0326f29 100644
--- a/manual/stdio.texi
+++ b/manual/stdio.texi
@@ -2428,7 +2428,7 @@ the array @var{s}, not including the terminating null character.
The behavior of this function is undefined if copying takes place
between objects that overlap---for example, if @var{s} is also given
as an argument to be printed under control of the @samp{%s} conversion.
-@xref{Copying and Concatenation}.
+@xref{Copying Strings and Arrays}.
@strong{Warning:} The @code{sprintf} function can be @strong{dangerous}
because it can potentially output more characters than can fit in the
diff --git a/manual/string.texi b/manual/string.texi
index 61ff3e2..fcb04c9 100644
--- a/manual/string.texi
+++ b/manual/string.texi
@@ -25,8 +25,9 @@ too.
* String/Array Conventions:: Whether to use a string function or an
arbitrary array function.
* String Length:: Determining the length of a string.
-* Copying and Concatenation:: Functions to copy the contents of strings
- and arrays.
+* Copying Strings and Arrays:: Functions to copy strings and arrays.
+* Concatenating Strings:: Functions to concatenate strings while copying.
+* Truncating Strings:: Functions to truncate strings while copying.
* String/Array Comparison:: Functions for byte-wise and character-wise
comparison.
* Collation Functions:: Functions for collating strings.
@@ -342,14 +343,13 @@ This function is a GNU extension and is declared in @file{string.h}.
This function is a GNU extension and is declared in @file{wchar.h}.
@end deftypefun
-@node Copying and Concatenation
-@section Copying and Concatenation
+@node Copying Strings and Arrays
+@section Copying Strings and Arrays
You can use the functions described in this section to copy the contents
-of strings and arrays, or to append the contents of one string to
-another. The @samp{str} and @samp{mem} functions are declared in the
-header file @file{string.h} while the @samp{wstr} and @samp{wmem}
-functions are declared in the file @file{wchar.h}.
+of strings, wide character strings, and arrays. The @samp{str} and
+@samp{mem} functions are declared in @file{string.h} while the
+@samp{w} functions are declared in @file{wchar.h}.
@pindex string.h
@pindex wchar.h
@cindex copying strings and arrays
@@ -360,8 +360,10 @@ functions are declared in the file @file{wchar.h}.
A helpful way to remember the ordering of the arguments to the functions
in this section is that it corresponds to an assignment expression, with
-the destination array specified to the left of the source array. All
-of these functions return the address of the destination array.
+the destination array specified to the left of the source array. Most
+of these functions return the address of the destination array; a few
+return the address of the destination's terminating null, or of just
+past the destination.
Most of these functions do not work properly if the source and
destination arrays overlap. For example, if the beginning of the
@@ -574,59 +576,6 @@ the strings overlap. The return value is the value of @var{wto}.
@end deftypefun
@comment string.h
-@comment ISO
-@deftypefun {char *} strncpy (char *restrict @var{to}, const char *restrict @var{from}, size_t @var{size})
-@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
-This function is similar to @code{strcpy} but always copies exactly
-@var{size} bytes into @var{to}.
-
-If the length of @var{from} is more than @var{size}, then @code{strncpy}
-copies just the first @var{size} bytes. Note that in this case
-there is no null terminator written into @var{to}.
-
-If the length of @var{from} is less than @var{size}, then @code{strncpy}
-copies all of @var{from}, followed by enough null bytes to add up
-to @var{size} bytes in all. This behavior is rarely useful, but it
-is specified by the @w{ISO C} standard.
-
-The behavior of @code{strncpy} is undefined if the strings overlap.
-
-Using @code{strncpy} as opposed to @code{strcpy} is a way to avoid bugs
-relating to writing past the end of the allocated space for @var{to}.
-However, it can also make your program much slower in one common case:
-copying a string which is probably small into a potentially large buffer.
-In this case, @var{size} may be large, and when it is, @code{strncpy} will
-waste a considerable amount of time copying null bytes.
-@end deftypefun
-
-@comment wchar.h
-@comment ISO
-@deftypefun {wchar_t *} wcsncpy (wchar_t *restrict @var{wto}, const wchar_t *restrict @var{wfrom}, size_t @var{size})
-@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
-This function is similar to @code{wcscpy} but always copies exactly
-@var{size} wide characters into @var{wto}.
-
-If the length of @var{wfrom} is more than @var{size}, then
-@code{wcsncpy} copies just the first @var{size} wide characters. Note
-that in this case there is no null terminator written into @var{wto}.
-
-If the length of @var{wfrom} is less than @var{size}, then
-@code{wcsncpy} copies all of @var{wfrom}, followed by enough null wide
-characters to add up to @var{size} wide characters in all. This
-behavior is rarely useful, but it is specified by the @w{ISO C}
-standard.
-
-The behavior of @code{wcsncpy} is undefined if the strings overlap.
-
-Using @code{wcsncpy} as opposed to @code{wcscpy} is a way to avoid bugs
-relating to writing past the end of the allocated space for @var{wto}.
-However, it can also make your program much slower in one common case:
-copying a string which is probably small into a potentially large buffer.
-In this case, @var{size} may be large, and when it is, @code{wcsncpy} will
-waste a considerable amount of time copying null wide characters.
-@end deftypefun
-
-@comment string.h
@comment SVID
@deftypefun {char *} strdup (const char *@var{s})
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{}}}
@@ -652,24 +601,6 @@ This function is a GNU extension.
@end deftypefun
@comment string.h
-@comment GNU
-@deftypefun {char *} strndup (const char *@var{s}, size_t @var{size})
-@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{}}}
-This function is similar to @code{strdup} but always copies at most
-@var{size} bytes into the newly allocated string.
-
-If the length of @var{s} is more than @var{size}, then @code{strndup}
-copies just the first @var{size} bytes and adds a closing null
-byte. Otherwise all bytes are copied and the string is
-terminated.
-
-This function is different to @code{strncpy} in that it always
-terminates the destination string.
-
-@code{strndup} is a GNU extension.
-@end deftypefun
-
-@comment string.h
@comment Unknown origin
@deftypefun {char *} stpcpy (char *restrict @var{to}, const char *restrict @var{from})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@@ -710,60 +641,6 @@ The behavior of @code{wcpcpy} is undefined if the strings overlap.
@comment string.h
@comment GNU
-@deftypefun {char *} stpncpy (char *restrict @var{to}, const char *restrict @var{from}, size_t @var{size})
-@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
-This function is similar to @code{stpcpy} but copies always exactly
-@var{size} bytes into @var{to}.
-
-If the length of @var{from} is more than @var{size}, then @code{stpncpy}
-copies just the first @var{size} bytes and returns a pointer to the
-byte directly following the one which was copied last. Note that in
-this case there is no null terminator written into @var{to}.
-
-If the length of @var{from} is less than @var{size}, then @code{stpncpy}
-copies all of @var{from}, followed by enough null bytes to add up
-to @var{size} bytes in all. This behavior is rarely useful, but it
-is implemented to be useful in contexts where this behavior of the
-@code{strncpy} is used. @code{stpncpy} returns a pointer to the
-@emph{first} written null byte.
-
-This function is not part of ISO or POSIX but was found useful while
-developing @theglibc{} itself.
-
-Its behavior is undefined if the strings overlap. The function is
-declared in @file{string.h}.
-@end deftypefun
-
-@comment wchar.h
-@comment GNU
-@deftypefun {wchar_t *} wcpncpy (wchar_t *restrict @var{wto}, const wchar_t *restrict @var{wfrom}, size_t @var{size})
-@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
-This function is similar to @code{wcpcpy} but copies always exactly
-@var{wsize} wide characters into @var{wto}.
-
-If the length of @var{wfrom} is more than @var{size}, then
-@code{wcpncpy} copies just the first @var{size} wide characters and
-returns a pointer to the wide character directly following the last
-non-null wide character which was copied last. Note that in this case
-there is no null terminator written into @var{wto}.
-
-If the length of @var{wfrom} is less than @var{size}, then @code{wcpncpy}
-copies all of @var{wfrom}, followed by enough null wide characters to add up
-to @var{size} wide characters in all. This behavior is rarely useful, but it
-is implemented to be useful in contexts where this behavior of the
-@code{wcsncpy} is used. @code{wcpncpy} returns a pointer to the
-@emph{first} written null wide character.
-
-This function is not part of ISO or POSIX but was found useful while
-developing @theglibc{} itself.
-
-Its behavior is undefined if the strings overlap.
-
-@code{wcpncpy} is a GNU extension and is declared in @file{wchar.h}.
-@end deftypefun
-
-@comment string.h
-@comment GNU
@deftypefn {Macro} {char *} strdupa (const char *@var{s})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
This macro is similar to @code{strdup} but allocates the new string
@@ -790,20 +667,35 @@ This function is only available if GNU CC is used.
@end deftypefn
@comment string.h
-@comment GNU
-@deftypefn {Macro} {char *} strndupa (const char *@var{s}, size_t @var{size})
+@comment BSD
+@deftypefun void bcopy (const void *@var{from}, void *@var{to}, size_t @var{size})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
-This function is similar to @code{strndup} but like @code{strdupa} it
-allocates the new string using @code{alloca}
-@pxref{Variable Size Automatic}. The same advantages and limitations
-of @code{strdupa} are valid for @code{strndupa}, too.
+This is a partially obsolete alternative for @code{memmove}, derived from
+BSD. Note that it is not quite equivalent to @code{memmove}, because the
+arguments are not in the same order and there is no return value.
+@end deftypefun
-This function is implemented only as a macro, just like @code{strdupa}.
-Just as @code{strdupa} this macro also must not be used inside the
-parameter list in a function call.
+@comment string.h
+@comment BSD
+@deftypefun void bzero (void *@var{block}, size_t @var{size})
+@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
+This is a partially obsolete alternative for @code{memset}, derived from
+BSD. Note that it is not as general as @code{memset}, because the only
+value it can store is zero.
+@end deftypefun
-@code{strndupa} is only available if GNU CC is used.
-@end deftypefn
+@node Concatenating Strings
+@section Concatenating Strings
+@pindex string.h
+@pindex wchar.h
+@cindex concatenating strings
+@cindex string concatenation functions
+
+The functions described in this section concatenate the contents of a
+string or wide character string to another. They follow the
+string-copying functions in their conventions. @xref{Copying Strings
+and Arrays}. @samp{strcat} is declared in the header file
+@file{string.h} while @samp{wcscat} is declared in @file{wchar.h}.
@comment string.h
@comment ISO
@@ -826,6 +718,8 @@ strcat (char *restrict to, const char *restrict from)
@end smallexample
This function has undefined results if the strings overlap.
+
+As noted below, this function has significant performance issues.
@end deftypefun
@comment wchar.h
@@ -849,10 +743,13 @@ wcscat (wchar_t *wto, const wchar_t *wfrom)
@end smallexample
This function has undefined results if the strings overlap.
+
+As noted below, this function has significant performance issues.
@end deftypefun
Programmers using the @code{strcat} or @code{wcscat} function (or the
-following @code{strncat} or @code{wcsncar} functions for that matter)
+@code{strncat} or @code{wcsncat} functions defined in
+a later section, for that matter)
can easily be recognized as lazy and reckless. In almost all situations
the lengths of the participating strings are known (it better should be
since how can one otherwise ensure the allocated size of the buffer is
@@ -977,6 +874,166 @@ should think twice and look through the program whether the code cannot
be rewritten to take advantage of already calculated results. Again: it
is almost always unnecessary to use @code{strcat}.
+@node Truncating Strings
+@section Truncating Strings while Copying
+@cindex truncating strings
+@cindex string truncation
+
+The functions described in this section copy or concatenate the
+possibly-truncated contents of a string or array to another, and
+similarly for wide character strings. They follow the string-copying
+functions in their header conventions. @xref{Copying Strings and
+Arrays}. The @samp{str} functions are declared in the header file
+@file{string.h} and the @samp{wc} functions are declared in the file
+@file{wchar.h}.
+
+@comment string.h
+@comment ISO
+@deftypefun {char *} strncpy (char *restrict @var{to}, const char *restrict @var{from}, size_t @var{size})
+@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
+This function is similar to @code{strcpy} but always copies exactly
+@var{size} bytes into @var{to}.
+
+If the length of @var{from} is more than @var{size}, then @code{strncpy}
+copies just the first @var{size} bytes. Note that in this case
+there is no null terminator written into @var{to}.
+
+If the length of @var{from} is less than @var{size}, then @code{strncpy}
+copies all of @var{from}, followed by enough null bytes to add up
+to @var{size} bytes in all.
+
+The behavior of @code{strncpy} is undefined if the strings overlap.
+
+This function was designed for now-rarely-used arrays consisting of
+non-null bytes followed by zero or more null bytes. It needs to set
+all @var{size} bytes of the destination, even when @var{size} is much
+greater than the length of @var{from}. As noted below, this function
+is generally a poor choice for processing text.
+@end deftypefun
+
+@comment wchar.h
+@comment ISO
+@deftypefun {wchar_t *} wcsncpy (wchar_t *restrict @var{wto}, const wchar_t *restrict @var{wfrom}, size_t @var{size})
+@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
+This function is similar to @code{wcscpy} but always copies exactly
+@var{size} wide characters into @var{wto}.
+
+If the length of @var{wfrom} is more than @var{size}, then
+@code{wcsncpy} copies just the first @var{size} wide characters. Note
+that in this case there is no null terminator written into @var{wto}.
+
+If the length of @var{wfrom} is less than @var{size}, then
+@code{wcsncpy} copies all of @var{wfrom}, followed by enough null wide
+characters to add up to @var{size} wide characters in all.
+
+The behavior of @code{wcsncpy} is undefined if the strings overlap.
+
+This function is the wide-character counterpart of @code{strncpy} and
+suffers from most of the problems that @code{strncpy} does. For
+example, as noted below, this function is generally a poor choice for
+processing text.
+@end deftypefun
+
+@comment string.h
+@comment GNU
+@deftypefun {char *} strndup (const char *@var{s}, size_t @var{size})
+@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{}}}
+This function is similar to @code{strdup} but always copies at most
+@var{size} bytes into the newly allocated string.
+
+If the length of @var{s} is more than @var{size}, then @code{strndup}
+copies just the first @var{size} bytes and adds a closing null
+byte. Otherwise all bytes are copied and the string is
+terminated.
+
+This function differs from @code{strncpy} in that it always
+terminates the destination string.
+
+As noted below, this function is generally a poor choice for
+processing text.
+
+@code{strndup} is a GNU extension.
+@end deftypefun
+
+@comment string.h
+@comment GNU
+@deftypefn {Macro} {char *} strndupa (const char *@var{s}, size_t @var{size})
+@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
+This function is similar to @code{strndup} but like @code{strdupa} it
+allocates the new string using @code{alloca}
+@pxref{Variable Size Automatic}. The same advantages and limitations
+of @code{strdupa} are valid for @code{strndupa}, too.
+
+This function is implemented only as a macro, just like @code{strdupa}.
+Just as @code{strdupa} this macro also must not be used inside the
+parameter list in a function call.
+
+As noted below, this function is generally a poor choice for
+processing text.
+
+@code{strndupa} is only available if GNU CC is used.
+@end deftypefn
+
+@comment string.h
+@comment GNU
+@deftypefun {char *} stpncpy (char *restrict @var{to}, const char *restrict @var{from}, size_t @var{size})
+@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
+This function is similar to @code{stpcpy} but copies always exactly
+@var{size} bytes into @var{to}.
+
+If the length of @var{from} is more than @var{size}, then @code{stpncpy}
+copies just the first @var{size} bytes and returns a pointer to the
+byte directly following the one which was copied last. Note that in
+this case there is no null terminator written into @var{to}.
+
+If the length of @var{from} is less than @var{size}, then @code{stpncpy}
+copies all of @var{from}, followed by enough null bytes to add up
+to @var{size} bytes in all. This behavior is rarely useful, but it
+is implemented to be useful in contexts where this behavior of the
+@code{strncpy} is used. @code{stpncpy} returns a pointer to the
+@emph{first} written null byte.
+
+This function is not part of ISO or POSIX but was found useful while
+developing @theglibc{} itself.
+
+Its behavior is undefined if the strings overlap. The function is
+declared in @file{string.h}.
+
+As noted below, this function is generally a poor choice for
+processing text.
+@end deftypefun
+
+@comment wchar.h
+@comment GNU
+@deftypefun {wchar_t *} wcpncpy (wchar_t *restrict @var{wto}, const wchar_t *restrict @var{wfrom}, size_t @var{size})
+@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
+This function is similar to @code{wcpcpy} but copies always exactly
+@var{wsize} wide characters into @var{wto}.
+
+If the length of @var{wfrom} is more than @var{size}, then
+@code{wcpncpy} copies just the first @var{size} wide characters and
+returns a pointer to the wide character directly following the last
+non-null wide character which was copied last. Note that in this case
+there is no null terminator written into @var{wto}.
+
+If the length of @var{wfrom} is less than @var{size}, then @code{wcpncpy}
+copies all of @var{wfrom}, followed by enough null wide characters to add up
+to @var{size} wide characters in all. This behavior is rarely useful, but it
+is implemented to be useful in contexts where this behavior of the
+@code{wcsncpy} is used. @code{wcpncpy} returns a pointer to the
+@emph{first} written null wide character.
+
+This function is not part of ISO or POSIX but was found useful while
+developing @theglibc{} itself.
+
+Its behavior is undefined if the strings overlap.
+
+As noted below, this function is generally a poor choice for
+processing text.
+
+@code{wcpncpy} is a GNU extension.
+@end deftypefun
+
@comment string.h
@comment ISO
@deftypefun {char *} strncat (char *restrict @var{to}, const char *restrict @var{from}, size_t @var{size})
@@ -1002,6 +1059,12 @@ strncat (char *to, const char *from, size_t size)
@end smallexample
The behavior of @code{strncat} is undefined if the strings overlap.
+
+As a companion to @code{strncpy}, @code{strncat} was designed for
+now-rarely-used arrays consisting of non-null bytes followed by zero
+or more null bytes. As noted below, this function is generally a poor
+choice for processing text. Also, this function has significant
+performance issues. @xref{Concatenating Strings}.
@end deftypefun
@comment wchar.h
@@ -1023,7 +1086,8 @@ wchar_t *
wcsncat (wchar_t *restrict wto, const wchar_t *restrict wfrom,
size_t size)
@{
- memcpy (wto + wcslen (wto), wfrom, wcsnlen (wfrom, size) * sizeof (wchar_t));
+ memcpy (wto + wcslen (wto), wfrom,
+ wcsnlen (wfrom, size) * sizeof (wchar_t));
wto[wcslen (to) + wcsnlen (wfrom, size)] = '\0';
return wto;
@}
@@ -1031,9 +1095,39 @@ wcsncat (wchar_t *restrict wto, const wchar_t *restrict wfrom,
@end smallexample
The behavior of @code{wcsncat} is undefined if the strings overlap.
-@end deftypefun
-Here is an example showing the use of @code{strncpy} and @code{strncat}
+As noted below, this function is generally a poor choice for
+processing text. Also, this function has significant performance
+issues. @xref{Concatenating Strings}.
+@end deftypefun
+
+Because these functions can abruptly truncate strings or wide
+character strings, they are generally poor choices for processing
+text. For example, if you use them to compute a user name, the
+truncated name can identify the wrong user. If you use them to copy
+or concatenate multibyte character strings, they can truncate within a
+multibyte character so that the result is not a valid multibyte
+character string. And if you use them to combine or concatenate
+multibyte or wide character strings, they may truncate the output
+after a combining character, resulting in a corrupted grapheme.
+
+Although these string-truncation functions have been used to fend off
+some buffer overruns, nowadays more-systematic techniques are often
+available, such as defining the @code{_FORTIFY_SOURCE} macro or using
+GCC's @option{-fsanitize=address} option. Ironically, use of these
+string-truncation functions can mask application bugs that would
+otherwise be caught by the more-systematic techniques.
+
+@strong{Note:} GNU programs should not use statically sized buffers
+for storing strings or wide character strings. @xref{Semantics, ,
+Writing Robust Programs, standards, The GNU Coding Standards}.
+Instead of string-truncation functions, it is usually better to use
+dynamic memory allocation (@pxref{Unconstrained Allocation}) and
+functions such as @code{strdup} or @code{asprintf} to construct
+strings.
+
+If despite the above comments you still want to use string-truncation functions,
+here is an example showing the use of @code{strncpy} and @code{strncat}
(the wide character version is equivalent). Notice how, in the call to
@code{strncat}, the @var{size} parameter is computed to avoid
overflowing the array @code{buffer}.
@@ -1050,24 +1144,6 @@ hello
hello, wo
@end smallexample
-@comment string.h
-@comment BSD
-@deftypefun void bcopy (const void *@var{from}, void *@var{to}, size_t @var{size})
-@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
-This is a partially obsolete alternative for @code{memmove}, derived from
-BSD. Note that it is not quite equivalent to @code{memmove}, because the
-arguments are not in the same order and there is no return value.
-@end deftypefun
-
-@comment string.h
-@comment BSD
-@deftypefun void bzero (void *@var{block}, size_t @var{size})
-@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
-This is a partially obsolete alternative for @code{memset}, derived from
-BSD. Note that it is not as general as @code{memset}, because the only
-value it can store is zero.
-@end deftypefun
-
@node String/Array Comparison
@section String/Array Comparison
@cindex comparing strings and arrays
@@ -1471,7 +1547,7 @@ to @var{size} bytes (including a terminating null byte) are
stored.
The behavior is undefined if the strings @var{to} and @var{from}
-overlap; see @ref{Copying and Concatenation}.
+overlap; see @ref{Copying Strings and Arrays}.
The return value is the length of the entire transformed string. This
value is not affected by the value of @var{size}, but if it is greater
@@ -1501,7 +1577,7 @@ selected for collation, and stores the transformed string in the array
wide character) are stored.
The behavior is undefined if the strings @var{wto} and @var{wfrom}
-overlap; see @ref{Copying and Concatenation}.
+overlap; see @ref{Copying Strings and Arrays}.
The return value is the length of the entire transformed wide character
string. This value is not affected by the value of @var{size}, but if
@@ -2111,8 +2187,8 @@ if the remainder of string consists only of delimiter wide characters,
@strong{Warning:} Since @code{strtok} and @code{wcstok} alter the string
they is parsing, you should always copy the string to a temporary buffer
-before parsing it with @code{strtok}/@code{wcstok} (@pxref{Copying and
-Concatenation}). If you allow @code{strtok} or @code{wcstok} to modify
+before parsing it with @code{strtok}/@code{wcstok} (@pxref{Copying Strings
+and Arrays}). If you allow @code{strtok} or @code{wcstok} to modify
a string that came from another part of your program, you are asking for
trouble; that string might be used for other purposes after
@code{strtok} or @code{wcstok} has modified it, and it would not have
--
2.1.0
>From 91d9c61dfa915d888c1e0e2010c2ddddbb1b4d34 Mon Sep 17 00:00:00 2001
From: Paul Eggert <eggert@cs.ucla.edu>
Date: Thu, 26 Nov 2015 01:54:20 -0800
Subject: [PATCH 3/3] Add strlcpy, strlcat
[BZ #178]
This patch was derived from text by Florian Weimer in:
https://sourceware.org/ml/libc-alpha/2015-11/msg00558.html
* manual/string.texi (Truncating Strings): New functions from BSD.
---
ChangeLog | 6 ++++
manual/string.texi | 84 +++++++++++++++++++++++++++++++++++++++++++++++++++++-
2 files changed, 89 insertions(+), 1 deletion(-)
diff --git a/ChangeLog b/ChangeLog
index e4f86e9..b76e781 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,11 @@
2015-11-26 Paul Eggert <eggert@cs.ucla.edu>
+ [BZ #178]
+ Add strlcpy, strlcat
+ This patch was derived from text by Florian Weimer in:
+ https://sourceware.org/ml/libc-alpha/2015-11/msg00558.html
+ * manual/string.texi (Truncating Strings): New functions from BSD.
+
Split large string section; add truncation advice
* manual/string.texi (Copying Strings and Arrays): Split into
three sections Copying Strings and Arrays, Concatenating Strings,
diff --git a/manual/string.texi b/manual/string.texi
index fcb04c9..80c2eda 100644
--- a/manual/string.texi
+++ b/manual/string.texi
@@ -748,7 +748,7 @@ As noted below, this function has significant performance issues.
@end deftypefun
Programmers using the @code{strcat} or @code{wcscat} function (or the
-@code{strncat} or @code{wcsncat} functions defined in
+@code{strlcat}, @code{strncat}, or @code{wcsncat} functions defined in
a later section, for that matter)
can easily be recognized as lazy and reckless. In almost all situations
the lengths of the participating strings are known (it better should be
@@ -911,6 +911,49 @@ greater than the length of @var{from}. As noted below, this function
is generally a poor choice for processing text.
@end deftypefun
+@comment string.h
+@comment BSD
+@deftypefun size_t strlcpy (char *restrict @var{to}, const char *restrict @var{from}, size_t @var{size})
+@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
+This function is similar to @code{strcpy}, but copies at most
+@var{size} bytes from the string @var{from} into the destination
+buffer @var{to}, including a terminating null byte if @var{size} is
+nonzero.
+
+If @var{size} is greater than the length of @var{from}, @code{strlcpy}
+copies all of the string @var{from} to the destination buffer @var{to},
+including the terminating null byte. Like other string functions such
+as @code{strcpy}, but unlike @code{strncpy}, any remaining bytes in
+the destination buffer remain unchanged.
+
+If @var{size} is nonzero and is not greater than the length of the
+string @var{from}, @code{strlcpy} copies only the first
+@samp{@var{size} - 1} bytes to the destination buffer @var{to}, and
+writes a terminating null byte to the last byte in the buffer.
+
+If @var{size} is zero, nothing is written to @var{to}.
+
+This function returns the length of @var{from}. This means that
+truncation occurs whenever the returned value is not less than
+@var{size}.
+
+The behavior of @code{strlcpy} is undefined if the strings overlap or
+if the source or destination are null pointers.
+
+Unlike @code{strncpy}, @code{strcpy} always null-terminates a nonempty
+destination buffer, does not zero-fill the destination buffer,
+requires @var{from} to be a null-terminated string, and always
+computes @var{from}'s length even when this length is greater than
+@var{size}.
+
+This function was designed as a stopgap for quickly retrofitting
+possibly-unsafe uses of @code{strcpy} on platforms lacking
+buffer-overrun protection. As noted below, this function is generally
+a poor choice for processing text.
+
+@code{strlcpy} is derived from BSD.
+@end deftypefun
+
@comment wchar.h
@comment ISO
@deftypefun {wchar_t *} wcsncpy (wchar_t *restrict @var{wto}, const wchar_t *restrict @var{wfrom}, size_t @var{size})
@@ -1067,6 +1110,45 @@ choice for processing text. Also, this function has significant
performance issues. @xref{Concatenating Strings}.
@end deftypefun
+@comment string.h
+@comment BSD
+@deftypefun size_t strlcat (char *restrict @var{to}, const char *restrict @var{from}, size_t @var{size})
+@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
+This function attempts to concatenate the string @var{from} to the
+destination array @var{to} of size @var{size}.
+
+If the original array @var{to} contains a null byte among the first
+@var{size} bytes, @code{strlcat} copies as much as possible of the
+string @var{from} into the buffer at @var{to} of @var{size} bytes,
+starting at the terminating null byte of the original string @var{to}.
+In effect, this appends a prefix of the string @var{from} to the
+string @var{to}. In this case, the resulting string in @var{to} will
+always be null-terminated, and it is truncated if necessary (not all
+bytes in @var{from} are copied). @code{strlcat} returns the sum of
+the original length of @var{to} and the length of @var{from}.
+
+If the original array @var{to} is not null-terminated (within the
+first @var{size} bytes of the array), @code{strlcat} returns
+@var{size} plus the length of the string @var{from}. In this case,
+the array @var{to} is unchanged, and is not null-terminated. This
+also covers the case when @var{size} is zero.
+
+Unlike @code{strncat}, @code{strlcat} keeps the destination buffer
+null-terminated if it was already null-terminated, requires @var{from}
+to be a null-terminated string, and always computes @var{from}'s
+length even when this length is greater than that of the appended
+string.
+
+As a companion to @code{strlcpy}, @code{strlcat} was designed as a
+stopgap for quickly retrofitting possibly-unsafe uses of @code{strcat}
+on platforms lacking buffer-overrun protection. As noted below, this
+function is generally a poor choice for processing text. Also, this
+function has significant performance issues. @xref{Concatenating
+Strings}.
+
+@code{strlcat} is derived from BSD.
+@end deftypefun
+
@comment wchar.h
@comment ISO
@deftypefun {wchar_t *} wcsncat (wchar_t *restrict @var{wto}, const wchar_t *restrict @var{wfrom}, size_t @var{size})
--
2.1.0