GCC and pointer overflows

GCC and pointer overflows

Of course, it fails for dynamically allocated and grown buffers since sizeof() can't tell you the length.

Also, you failed to account for element size. The following should work, though, for arrays of static size:

    if (len > (sizeof(buf) / sizeof(buf[0]))
       die_in_a_fire();

I don't understand why you have the bitwise negation operator in there. Also, len is a length, not a pointer type, so pointer format doesn't matter.

The question was how to check if arithmetic overflowed/wrapped, not whether an index or length
is valid.