Interesting gcc/clang extensions to C
Both gcc and clang support extensions to C and while i normally try and make things I write about work on Windows (i.e. Visual Studio), these are useful enough that I thought they deserve a mention. Yes I know you can run gcc/clang on Windows using Cygwin or MinGW, but for various reasons I prefer Visual Studio.
You can add a constructor and destructor functions to a C program; the constructor function runs before main() and the destructor after main().
The syntax is not exactly clean or obvious (those are double underscores before and after the word attribute like Python dunders!) but I got this program to compile/run with clang 10 on Ubuntu as the screenshot shows. Here’s a listing. I called the two functions ctor and dtor but you can use anything.
#include <stdio.h>
__attribute__((constructor)) void ctor(void)
{
printf("Constructor runs first\n");
}
__attribute__((destructor)) void dtor(void)
{
printf("Destructor runs last\n");
}
int main() {
printf("Main\n");
}The output is:
david@DavidPC:~/Projects/Examples$ ./ex1 Constructor runs first Main Destructor runs last
It has been a few months since I last used it and as you’d expect, it took a little bit of time and effort to get things back to what they were.
I originally created Asteroids for Windows using Visual Studio 2017 Community Edition. Since then I’ve started the Clang version on Ubuntu and there haven’t been too many differences but there are just a few so in this post I’ll list what I’ve found so far.