Using SDL2_gfx issues using C++

Question

When I use SDL2_gfx with the common.c /common.h files that are included with it, and then use the cpp instead of c extension using VS201X, I get the LNK2019: unresolved external symbol _SDL_main

What that means is if I change the file containing main to test.c, it compiles. When I change it back to text.cpp it fails to compile. I think that indicates that it only works as C, and not C++.

Below is the code I copied from SDL2_gfxPrimitives.c (Spaces added so they would show up):

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
#include <time.h>

#include "common.h"

#include "SDL2_gfxPrimitives.h"

static CommonState *state;

int main(int argc, char* argv[])
{
/* Initialize test framework */
state = CommonCreateState(argv, SDL_INIT_VIDEO);

return 1;
}

I need to use the library in C++ but it seems I don't know enough to figure out how. Any help would be appreciated, I've spent two days attempting to figure this out.

Answer 1

This is a little bit of a gotcha for SDL.

What it does is #define main SDL_main

This renames int main(int argc, char *argv[]) into int SDL_main(int argc, char *argv[]).

In order to use it, SDL wants an unmangled SDL_main to link against, and because you simply renamed the test.c -> test.cpp, you didn't add the code to cause this to happen.

It's described in the documentation:

The application's main() function must be called with C linkage, and should be declared like this:

 #ifdef __cplusplus 
 extern "C" 
 #endif 
 int main(int argc, char *argv[]) 
 { 
 } 

so if you put the:

#ifdef __cplusplus
extern "C"
#endif

immediately before the declaration of the main function, it should link correctly.