Formatting `nullptr` on out stream as hexadecimal address, instead of `0`

Question

How can I format a null pointer of any type, preferably including immediate nullptr, on out stream so it prints out like 0x000000000000 or even just 0x0 but something resembling an address value instead of a senseless 0 or terminate or whatever non-address-like? //(nil) or (null) I could accept too if not using printf.

Answer 1

You can make a pointer formatter, which can do the formatting in whatever way you prefer.

For example:

#include <cstdint>
#include <iomanip>
#include <ios>
#include <iostream>
#include <sstream>
#include <string>

static auto Fmt(void const* p) -> std::string {
    auto value = reinterpret_cast<std::uintptr_t>(p);
    constexpr auto width = sizeof(p) * 2;
    std::stringstream ss;
    ss << "0x" << std::uppercase << std::setfill('0') << std::setw(width) << std::hex << value;
    return ss.str();
}

int main() {
    char const* p = nullptr;
    std::cout << Fmt(p) << "\n";
    p = "Hello";
    std::cout << Fmt(p) << "\n";
}