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c++arrayspointerscomparison

Can you use relational operators to check whether a pointer points to an object within an array?

Can I check whether or not a given pointer points to an object within an array, specified by its bounds?

template <typename T>
bool points_within_array(T* p, T* begin, T* end)
{
    return begin <= p && p < end;
}

Or do the pointer comparisons invoke undefined behavior if p points outside the bounds of the array? In that case, how do I solve the problem? Does it work with void pointers? Or is it impossible to solve?

Solution

  • Although the comparison is valid only for pointers within the array and "one past the end", it is valid to use a set or map with a pointer as the key, which uses std::less<T*>

    There was a big discussion on this way back in 1996 on comp.std.c++