Re: buffer overflow

Roman Mashak wrote:

can't realize what's happening in this code snippet:

int main(int argc, char *argv[])
{
char buf[256];
strcpy(buf, argv[1]);
...
}

Debugger shows argv[1] as NULL and as a result I get 'segmentation
fault' on 'strcpy' call. I can't figure out why NULL is not a proper
in this case, standard doesn't prohibit it in string functions (at
least I have not found it).

However the standard does require a proper string to copy into
buf. A string is a sequence of bytes, possibly empty, followed by
a '\0' byte. A NULL pointer doesn't point to anything, so there is
no place for that '\0'. So you need a statement such as:

if (argv[1]) strcpy(buf, argv[1]);
else buf[0] = '\0';

Of course argv[1] may not even exist, so you should also guard by:

if (argc > 1) ...

--
Chuck F (cbfalconer at maineline dot net)
Available for consulting/temporary embedded and systems.
<http://cbfalconer.home.att.net>


.

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