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[Bug manual/431] New: description and example for strncat is incorrect and error prone
- From: "gmane at chqrlie dot org" <sourceware-bugzilla at sources dot redhat dot com>
- To: glibc-bugs at sources dot redhat dot com
- Date: 8 Oct 2004 09:25:22 -0000
- Subject: [Bug manual/431] New: description and example for strncat is incorrect and error prone
- Reply-to: sourceware-bugzilla at sources dot redhat dot com
The description for function strncat in section "Copying and Concatenation" of
the glibc manual states that strncat can be implemented this way:
char *strncat (char *to, const char *from, size_t size){
to[strlen (to) + size] = '\0';
strncpy (to + strlen (to), from, size);
return to;
}
This is incorrect as more than strlen(from)+1 characters are appended to the
destination array "to". It conficts with the C99 description : appended
characters are said to come from "from" and that NUL and subsequent characters
are not copied.
The implementation in string/bits/string2.h does not contain this erroneous
behaviour.
Furthermore, the example provided for strncpy and strncat just below is typical
of bad programming practice, leading unsuspecting readers to produce buggy code:
- the propotype for main without a return type (or void) is deprecated, and
incorrect by C99 standard.
- the assumption made in this code that SIZE be larger than strlen("hello") is
implicit and undocumented! If it were not the case, buffer would not be NUL
terminated and both puts and strlen would have undefined behaviour, and strncat
would very likely produce a buffer overflow.
It sets a bad example. I have seen so many programmers bitten by this kind of
code, even savvy hackers, that I think it does not belong in the GNU libc
manual.
As a matter of fact, I think strncpy and strncat should be described as error
prone and frowned upon.
Chqrlie
--
Summary: description and example for strncat is incorrect and
error prone
Product: glibc
Version: unspecified
Status: NEW
Severity: normal
Priority: P2
Component: manual
AssignedTo: roland at gnu dot org
ReportedBy: gmane at chqrlie dot org
CC: glibc-bugs at sources dot redhat dot com
http://sources.redhat.com/bugzilla/show_bug.cgi?id=431
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