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September 26, 2005

On being overly cautious

Most of us have least heard of buffer overflows, and all C programmers ought to pay attention to the size of target arrays and never attempt to put more in them than they have capacity for. Using something like: 

strcpy(targetbuf, ptr);        // might be dangerous

is — in general — asking for trouble because one doesn't know whether the pointed-to string (ptr) will actuallyfit in the target space. So many developers use size-limited functions that insure there won't be any overflow.

One of these is snprintf, which performs a printf-like copy to a buffer, but the buffer's size is included: 

snprintf(targetbuf, targetsize, "message %d %s", i, p);  // safer!

and it guarantees that it won't write beyond that. It's a wise technique, but one can be overly cautious about it. This was seen in code today (multiple times): 

snprintf(result_string, BUFSIZE-1, "%s", "U");

I'll leave it as an exercise to the reader to find better ways to handle this particular circumstance.

Posted by steve at September 26, 2005 09:42 AM

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Comments

slprintf ;)

Posted by: omerm at October 8, 2005 09:11 AM