g++check.cpp

#include<iostream>

int main() {
    if (__cplusplus == 202101L) std::cout << "C++23";
    else if (__cplusplus == 202002L) std::cout << "C++20";
    else if (__cplusplus == 201703L) std::cout << "C++17";
    else if (__cplusplus == 201402L) std::cout << "C++14";
    else if (__cplusplus == 201103L) std::cout << "C++11";
    else if (__cplusplus == 199711L) std::cout << "C++98";
    else std::cout << "pre-standard C++." << __cplusplus;
    std::cout << "\n";
}