Re: [Valgrind-users] The bug that got away...

[Florian Krohm]

On 11/01/2011 06:33 PM, Peter Toft wrote:
>  Hi all
> 
>  Try to find the errors in this C/C++ snippet using valgrind:
> 
>  #include <stdio.h>
>  /* Save as code.c */
>  int main(void)
>  {
>   int i=-1,a[2],b[2],c[2];
>   a[0] = 1; a[1] = 2;
>   b[0] = 3; b[1] = 4;
>   c[0] = 5; c[1] = 6;
>   printf("%i %in",b[i],a[i]);
>   return 0;
>  }
> 
>  Compile using "gcc -o bla code.c -Wall" and check the code using 
>  "valgrind ./bla".
>  Valgrind finds nothing even though I index a[-1] and b[-1] - not 
>  good...
> 

Not good. But expected. Memcheck, the default valgrind tool, does not
find array overruns on variables allocated on the stack.
You might want to try ptrcheck:
http://valgrind.org/docs/manual/pc-manual.html#pc-manual.how-works.sg-checks

>  Insure++ would for sure find the negative index, but GCC nor Valgrind 
>  will get it...
> 

It's lame that GCC does not find it. Try clang. I wouldn't be surprised,
if it catches this error but I haven't tried it.

   Florian

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