[C++] Using std::bit_cast to convert byte arrays to values and back again

A common method of concatenating bytes is to use bit shifts and the | operator. This can be tedious and potentially fail if there aren’t 8 bits in a byte on your platform.

A more efficient method is to use std::bit_cast which reinterprets the bits of one datatype into another.

#include <array>
#include <bit>

auto join(std::array<char, 4> chars) -> int {
    return std::bit_cast<int>(chars);
}

auto split(int num) -> std::array<char, 4> {
    return std::bit_cast<std::array<char, 4>>(num);
}

With compiler optimisations enabled, it can be implemented with a single instruction.

chars$ = 8
int join(std::array<char,4>) PROC                    ; join, COMDAT
        mov     eax, ecx
        ret     0
int join(std::array<char,4>) ENDP                    ; join

num$ = 8
std::array<char,4> split(int) PROC       ; split, COMDAT
        mov     eax, ecx
        ret     0
std::array<char,4> split(int) ENDP       ; split