Can reserved function names be overloaded?

Question

This question is a follow-up question of this one.

Consider the following program:

#include <cmath>

// meaningless, only for language-lawyer purpose
void abs(void*) {}

int main(){
    abs(nullptr);
}

Does this program result in undefined behavior?

---

The related part in the standard is [extern.names]/4:

Each function signature from the C standard library declared with external linkage is reserved to the implementation for use as a function signature with both extern "C" and extern "C++" linkage, or as a name of namespace scope in the global namespace.

I'm not sure whether overloading is permitted.

Answer 1

There are two parts to this statement, as it talks about names (from the C standard) that are reserved (for C++ implementations). In particular,

Part 1: Each function signature from the C standard library declared with external linkage

This includes the C library function abs

Part 2: is reserved to the implementation for use as a function signature with both extern "C" and extern "C++" linkage, or as a name of namespace scope in the global namespace.

So the name ::abs is reserved for the C++ implementation. You can't use it. Overloading is irrelevant.