How do I safely and sensibly determine whether a pointer points somewhere into a specified buffer?

Question

I\'m looking to implement a function that determines whether a given pointer points into a given buffer. The specification:

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template          


        

Answer 1

If you cast the pointers to large enough unsigned integers and add number of bytes instead of number of objects, the undefined behavior goes away.

template 
bool points_into_buffer (T *p, T *buf, std::size_t len) {
    uintptr_t ip = (uintptr_t)p;
    uintptr_t ibuf = (uintptr_t)buf;
    return ip >= ibuf && ip < (ibuf + sizeof(T) * len);
}

This code doesn't detect if p is not correctly aligned, but you could easily add a test with a %.