A quick google got me this
http://www.ciselant.de/projects/gcc_printf/gcc_printf.html
seems its a feature of gcc. In certain circumstances it optimizes the printf
call to a puts call. While printf behaves nicely and prints '(null)' when
you pass it a null pointer, puts doesnt do that. From the document above
when "%s\n" is found in the format string it is optimized to a puts call.
Its interesting to note that the optimization is disabled if the printf
return value is assigned. So
replacing
printf("%s\n",p);
with
ret=printf("%s\n",p);
doesn't segfault.
-Ershaad
On Wed, Jun 18, 2008 at 3:22 PM, Wang Yu <[EMAIL PROTECTED]> wrote:
> Hi, all
> I have the following code:
> #include
> <stdio.h>
>
> int
> main()
>
> {
>
>
>
> char
> *p;
>
> p =
> 0;
>
> *printf("%s",
> p);
>
> printf("\n"); *
>
> return
> 0;
>
> }
>
> The out put is *(null)*
> But, if I change into:
>
> #include
> <stdio.h>
>
>
> int
> main()
>
> {
>
>
>
> char
> *p;
>
> p =
> 0;
>
> * printf("%s\n", p); *
>
>
> return
> 0;
>
> }
>
> The output will be* Segment fault*!
>
> I don't know why....
> Thanks!
> --
> National Research Center for Intelligent Computing Systems
> Institute of Computing Technology, Chinese Academy of Sciences
