Date: Wed, 24 Feb 2010 15:25:11 +0100 From: Max Laier <max@love2party.net> To: freebsd-hackers@freebsd.org Cc: Andrey Zonov <andrey.zonov@gmail.com> Subject: Re: 2 bytes allocated problems Message-ID: <201002241525.11930.max@love2party.net> In-Reply-To: <983a1cf21002240544s59006035ifbf0ef7eb045e44f@mail.gmail.com> References: <983a1cf21002240544s59006035ifbf0ef7eb045e44f@mail.gmail.com>
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On Wednesday 24 February 2010 14:44:35 Andrey Zonov wrote:
> Hi,
>
> When I try allocated pointer to a pointer, and in it some pointers
> (important: size is 2 bytes), the pointers lose their boundaries.
> Why it can happen?
>
> Test program in attach.
Your test program is broken:
>#define S1 "ab"
>#define S2 "cd"
>
> pp = (char **) Malloc(2 * sizeof(char *));
>
> pp[0] = (char *) malloc(2);
> memcpy(pp[0], S1, 2);
> pp[1] = (char *) malloc(2);
> memcpy(pp[1], S2, 2);
>
> printf("%s\n", *pp);
> printf("%s\n", pp[0]);
> printf("%s\n", pp[1]);
Why should *pp == pp[0], or pp[1] be a nul-terminated string? You just copied
the two characters. It's pure luck if there is a \0 at the end of any of
these elements, or that the access doesn't cause a SEGV.
If you do:
> pp[0] = (char *) malloc(3);
> memcpy(pp[0], S1, 3);
> pp[1] = (char *) malloc(3);
> memcpy(pp[1], S2, 3);
instead, you copy the termination and things work as expected.
Regards,
Max
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