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Re: problem with malloc?

In <>, on
   at 07:44 PM, Kaz Kylheku <> said:

>On Fri, 21 Apr 2000, Fred Heitkamp wrote:

>> Got electric fence.  Thanks!
>> I found the problem.  It was a buffer overrun in strcpy.
>> My data file that my program reads was written by a fortran program 
>> I think.  Strlen seems to give the correct answer as far as actual number
>> of characters (20) , but strcpy tries to copy the whole line which is
>> 62 characters.  Probably the length of the fortran record.

>That is simply not possible. If strlen returns 20, then strcpy will copy
>20 bytes plus one null byte.

>> I put strncpy for strcpy and the program runs fine.

I just didn't do a blind substitution.  I change the code to  essentially

len = strnlen( buffer );
target = ( char * )malloc( (len+1)*sizeof( char ) );
strncpy( target, buffer, len );

>You can't blindly substitute one for the other. The strncpy function does
>not ensure null termination of the target array in all cases.

Yeah I know.  I read the man page.  I wasn't too worried about the NULL
termination right at the moment.  I wanted to find the source of the seg.
fault.  I think I could just do something like 

strcat( target ,'\0' );

assuming the target buffer is big enough that is.

>The sprintf function can be leveraged to do a limited copy with proper
>null termination, though this in itself is tricky enough to be wrapped
>with a macro or function.

>    #include <stdio.h>

>    int lstrcpy(char *target, const char *source, size_t targetbufsize)
>    {
>	return sprintf(target, "%.*s", (int) (targetbufsize - 1), source);
>    }

Do you think the disparity in calculating the len, strlen vs
what strcpy does is a bug?  Probably not, but I thought I'd


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