Your C compiler's version and default language standard

While easy to determine the version of a compiler being used:

macOS-prompt> cc --version
Apple clang version 15.0.0 (clang-1500.0.40.1)
Target: arm64-apple-darwin23.0.0
Thread model: posix

Ubuntu-prompt> cc --version
cc (Ubuntu 12.3.0-1ubuntu1~23.04) 12.3.0

compiler front-ends support many languages and versions, so knowing the compiler's version is not much use. Instead, we need to know how our source code is being compiled, at compile time. We can test against the __STDC_VERSION__ preprocessor token, and then (possibly) compile different code/functions in our program:

#include <stdio.h>

int main(int argc, char *argv[])
{
#if __STDC_VERSION__ >=  201710L
    printf("hello from C18!\n");

#elif __STDC_VERSION__ >= 201112L
    printf("hello from C11!\n");

#else
    #error This program demands features from C11 or later

/*
#elif __STDC_VERSION__ >= 199901L
    printf("hello from C99!\n");
#else
    printf("hello from (ANSI-C) C89/C90!\n");
 */

#endif

    return 0;
}

This assists our goal of portable programming by ensuring that a program's required features are supported by the local compiler, and its default compilation arguments.