How to retrieve the user's state home directory on desktop OSs?

Question

I need to create and then write to a log file (using the spdlog library) but it needs to be created in the correct directory on every OS (macOS, Linux, Windows). For instance, on Linux, it's recommended to use "$HOME/.local/state" according to the XDG Base Directory Specification.

Here is an MRE of the code I've written (that works on Linux) however I'm not sure how correct it is:

#include <string_view>
#include <filesystem>
#include <iostream>
#include <cstdlib>
#include <unistd.h>
#include <pwd.h>
#include <glib.h>


int main( )
{
    constexpr std::string_view log_file_name { "basic-log.txt" };
    std::string_view home_dir;
    std::string_view logs_dir;

#if defined(__linux__) && !defined(__ANDROID__)
    if ( const gchar* const xdg_state_home { g_get_user_state_dir( ) }; xdg_state_home != nullptr )
    {
        home_dir = xdg_state_home;
        logs_dir = "My-App/logs";
    }
    else if ( const char* const user_home { std::getenv( "HOME" ) }; user_home != nullptr )
    {
        home_dir = user_home;
        logs_dir = ".local/state/My-App/logs";
    }
    else
    {
        home_dir = getpwuid( getuid( ) )->pw_dir;
        logs_dir = ".local/state/My-App/logs";
    }
#elif defined(_WIN32) || defined(_WIN64)
#   error "Windows code not fully implemented yet."
#elif defined(__APPLE__)
#   error "macOS code not fully implemented yet."
#else
#   error "Unsupported OS"
#endif

    std::filesystem::path log_file_path;
    log_file_path /= home_dir;
    log_file_path /= logs_dir;
    log_file_path /= log_file_name;

    std::cout << log_file_path << '\n';
}

What would be the equivalent implementations for Windows and macOS respectively?