Why is Visual C++ 2010 complaining about 'Using uninitialized memory'?

Question

I've got a function that takes a pointer to a buffer, and the size of that buffer (via a pointer). If the buffer's not big enough, it returns an error value and sets the required length in the out-param:

// FillBuffer is defined in another compilation unit (OBJ file).
// Whole program optimization is off.
int FillBuffer(__int_bcount_opt(*pcb) char *buffer, size_t *pcb);

I call it like this:

size_t cb = 12;
char *p = (char *)malloc(cb);
if (!p)
    return ENOMEM;

int result;
for (;;)
{
    result = FillBuffer(p, &cb);
    if (result == ENOBUFS)
    {
        char *q = (char *)realloc(p, cb);
        if (!q)
        {
            free(p);
            return ENOMEM;
        }

        p = q;
    }
    else
        break;
}

Visual C++ 2010 (with code analysis cranked to the max) complains with 'warning C6001: Using uninitialized memory 'p': Lines: ...'. It reports line numbers covering pretty much the entire function.

Visual C++ 2008 doesn't. As far as I can tell, this code's OK. What am I missing? Or what is VC2010 missing?

Answer 1

You did not check if the first malloc() is ok. This leads to the warning.

Answer 2

This has to be a bug in VS.2010. Wrapping malloc removes the warning:

char * mymalloc(int i)
{
return (char *) malloc(i);
}

...

void *r = mymalloc(cb);

char *p;

p = (char *) malloc(cb)

Makes the warning go away