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NNTP-Posting-Date: Mon, 16 May 2011 06:17:24 -0500
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Date: Mon, 16 May 2011 07:17:21 -0400
From: pete <pfiland@mindspring.com>
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Subject: Re: I need help
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Xref: x330-a1.tempe.blueboxinc.net comp.lang.c:4064

janus wrote:
> 
> > --
> > Ian Collins
> You must not use the macro STRNCAT in e.g. this case:
> 
> void a_procedure(char *a)
>   {
>   STRNCAT(a, "Jersey");
>   }
> 
> int main(void)
>   {
> 
>   char string[10] = "NEW";
>   a_procedure(string);
>   }
> 
> Here sizeof(a) is the size of a pointer
> and not the size of string. Instead
> you could do it without the macro:
> 
> void a_procedure(char *a, size_t size)
>   {
>   strncat(a, "Jersey", size - strlen(a) - 1);
>   }
> 
> int main(void)
>   {
> 
>   char string[10] = "NEW";
>   a_procedure(string, sizeof(string))
> 
> On Monday, May 16, 2011 11:26:30 AM UTC+1, Heinrich Wolf wrote:
> > "Ian Collins" <ian-...@hotmail.com> schrieb im Newsbeitrag
> > news:93bdoaFlpiU2@mid.individual.net...
> > > On 05/15/11 06:29 AM, Heinrich Wolf wrote:
> > >>
> > >> or with a macro:
> > >>
> > >> #define STRNCAT(a, b) strncat(a, b, sizeof(a) - strlen(a) - 1)
> > >> char string[10] = "NEW";
> > >> STRNCAT(string, "Jersey");
> > >
> > > That macro would go horribly (and silently) wrong if
> > >
> > > a) 'a' wasn't a fixed sized array, or
> > > b) it was, but the definition wasn't visible
> > >    when the macro was expanded.
> > >
> > > --
> > > Ian Collins
> >
> > You must not use the macro STRNCAT in e.g. this case:
> >
> > void a_procedure(char *a)
> >   {
> >   STRNCAT(a, "Jersey");
> >   }
> >
> > int main(void)
> >   {
> >
> >   char string[10] = "NEW";
> >   a_procedure(string);
> >   }
> >
> > Here sizeof(a) is the size of a pointer
> > and not the size of string. Instead
> > you could do it without the macro:
> >
> > void a_procedure(char *a, size_t size)
> >   {
> >   strncat(a, "Jersey", size - strlen(a) - 1);
> >   }
> >
> > int main(void)
> >   {
> >
> >   char string[10] = "NEW";
> >   a_procedure(string, sizeof(string));
> >   }
> 
> I do not see any difference between the two

Try harder.

-- 
pete