Question

This is the only way to test if the return string is empty. Each fails in the other’s architecture. The question is why? Why does !=NULL fail on x86 and _tcslen(*sDateOut)>0 fail on x64?:

BOOL FormatDate(TCHAR *sIn, TCHAR **sOut) {
free(*sOut);*sOut=NULL; // Clear

...
if (condition1)
    *sOut = calloc(length,sizeof(TCHAR);
...

#ifdef WIN64
    return (*sOut != NULL);
#else
    return (_tcslen(*sOut)>0);
#endif
}

Answer 1

If you want to check for an empty string you should compare the first character with '\0', not NULL.

The reason for this is because NULL is supposed to represent a null pointer – it’s actual value may not actually be zero.

---

Now back to the example, if you want to test if TCHAR **sOut is a valid pointer to an empty string this test should work:

if (sOut && *sOut && (*sOut)[0] != _T('\0')) {
    // non-empty
} else {
    // empty or invalid pointer
}