sizeof std::optional<T>

optional.cpp

#include <iostream>
#include <string>
#include <optional>

int main()
{
    std::cout << "sizeof bool is " << sizeof(bool) << '\n';
    std::cout << "sizeof std::optional<bool> is " << sizeof(std::optional<bool>) << "\n\n";

    std::cout << "sizeof short is " << sizeof(short) << '\n';
    std::cout << "sizeof std::optional<short> is " << sizeof(std::optional<short>) << "\n\n";

    std::cout << "sizeof int is " << sizeof(int) << '\n';
    std::cout << "sizeof std::optional<int> is " << sizeof(std::optional<int>) << "\n\n";

    std::cout << "sizeof int64_t is " << sizeof(int64_t) << '\n';
    std::cout << "sizeof std::optional<int64_t> is " << sizeof(std::optional<int64_t>) << "\n\n";

    std::cout << "sizeof void* is " << sizeof(void*) << '\n';
    std::cout << "sizeof std::optional<void*> is " << sizeof(std::optional<void*>) << "\n\n";

    std::cout << "sizeof std::string is " << sizeof(std::string) << '\n';
    std::cout << "sizeof std::optional<std::string> is " << sizeof(std::optional<std::string>) << "\n\n";
}

output.md

On GCC 7.2:

sizeof bool is 1
sizeof std::optional<bool> is 2

sizeof short is 2
sizeof std::optional<short> is 4

sizeof int is 4
sizeof std::optional<int> is 8

sizeof int64_t is 8
sizeof std::optional<int64_t> is 16

sizeof void* is 8
sizeof std::optional<void*> is 16

sizeof std::string is 32
sizeof std::optional<std::string> is 40