Problem with C++, SDL and Code::Blocks

Malkom · 04-22-2011, 08:26 PM

Hi.

First, this is my first post. Yay!

Okay, to business. I have a extremely irritating problem with getting Code::Blocks to compile my C++ SDL code. Here it is:

Code:

// Main program file of the SDL test.

#include <SDL.h>
#include <stdio.h>
#include <cstdlib>

int main() {
    SDL_Init(SDL_INIT_VIDEO);

    atexit(SDL_Quit);

    SDL_Surface *screen;

    screen = SDL_SetVideoMode(300, 300, 8, SDL_SWSURFACE);

    if(screen == NULL) {
        printf("Fatal error: Screen initialization failed.\n");
        exit(1);
    }

    atexit(SDL_Quit);

    

    return 0;
}

// This was copied straight from the SDL API Reference Guide. We'll
// see if it compiles...
void putpixel(SDL_Surface *surface, int x, int y, Uint32 pixel)
{
    int bpp = surface->format->BytesPerPixel;
    /* Here p is the address to the pixel we want to set */
    Uint8 *p = (Uint8 *)surface->pixels + y * surface->pitch + x * bpp;

    switch(bpp) {
    case 1:
        *p = pixel;
        break;

    case 2:
        *(Uint16 *)p = pixel;
        break;

    case 3:
        if(SDL_BYTEORDER == SDL_BIG_ENDIAN) {
            p[0] = (pixel >> 16) & 0xff;
            p[1] = (pixel >> 8) & 0xff;
            p[2] = pixel & 0xff;
        } else {
            p[0] = pixel & 0xff;
            p[1] = (pixel >> 8) & 0xff;
            p[2] = (pixel >> 16) & 0xff;
        }
        break;

    case 4:
        *(Uint32 *)p = pixel;
        break;
    }
}

I'm pretty sure the problem is with the code. The sample SDL project that C::B created for me runs fine with its default code, but when I plug mine into main.cpp it fails to compile with the following error message:

Code:


C:\MinGW32\lib\libSDLmain.a(SDL_win32_main.o)||In function `console_main':|
\Users\hercules\trunk\SDL-1.2\.\src\main\win32\SDL_win32_main.c|315|undefined reference to `SDL_main'|
||=== Build finished: 1 errors, 0 warnings ===|

Since it caused the same project that compiled the sample code to fail to compile this code, I'm sure that it was the code causing the problem. However, I've tried a number of things and been unable to fix it. Could you people give me a hand with this?

Thanks in advance.

dwhitney67 · 04-22-2011, 09:49 PM

Welcome to LQ.

The following is not a compilation issue; it is a linking issue.

Code:

... undefined reference to `SDL_main'

Anytime you see the "undefined reference" message, it is indicating to you that the function cannot be found. It may be due to cases where you have failed to implement the function, or it may be a case where you have failed to instruct the linker as to where it may find the function.

In your case, the linker is failing to find the SDL function which is implemented in an external library, notably libSDL.so. You need to figure out how to tell Code::Blocks that it needs to reference this library; typically one would specify "-lSDL", however it is better to specify "pkg-config --libs sdl". Similarly, for compiler flags, one specifies "pkg-config --cflags sdl".

I could tell you in a snap how to build your project from the command line, however since you are using and IDE, for which I care to know nothing about, I would expect you to RTFM concerning Code::Blocks on how to configure your compiler and linker options.

Malkom · 04-22-2011, 09:54 PM

DARN it, read the WHOLE POST, man!
The sample app compiled fine, but my code did NOT! I DID add SDL to the linker links.

dwhitney67 · 04-22-2011, 10:03 PM

Quote:

Originally Posted by Malkom

DARN it, read the WHOLE POST, man!
The sample app compiled fine, but my code did NOT! I DID add SDL to the linker links.

Not according to the linker error you posted. Or are you wasting my time?

alexcg · 04-23-2011, 01:27 PM

Which libraries do you link against and in which order?

alexcg · 04-23-2011, 01:41 PM

Also, try to change the definition of the main function to:

Code:

int main(int argc, char *argv[])
{
  // put your code here
}

MTK358 · 04-23-2011, 03:05 PM

Quote:

Originally Posted by alexcg

Also, try to change the definition of the main function to:

Code:

int main(int argc, char *argv[])
{
  // put your code here
}

I often omit the arguments to main() and everything works fine. As far as I know it's not wrong to omit them.

alexcg · 04-23-2011, 03:31 PM

Quote:

Originally Posted by MTK358

I often omit the arguments to main() and everything works fine. As far as I know it's not wrong to omit them.

It's not wrong to omit them until you are writing a Windows application that uses the SDL library

As far as I remember the SDLmain.lib contains the WinMain function (which is often the entry point of a Windows application), which calls the main function and passes two arguments - argc and argv.

MTK358 · 04-23-2011, 03:38 PM

Quote:

Originally Posted by alexcg

It's not wrong to omit them until you are writing a Windows application that uses the SDL library

As far as I remember the SDLmain.lib contains the WinMain function (which is often the entry point of a Windows application), which calls the main function and passes two arguments - argc and argv.

I didn't know that.

But the OP is using MinGW. Is that like a Linux environment for Windows (or is it just a port of GCC, etc)? If so, then it needs to be written like a Linux SDL application.

alexcg · 04-23-2011, 03:55 PM

Quote:

Originally Posted by MTK358

Is that like a Linux environment for Windows?

No, it isn't. MinGW is just a port of GCC for writing native Windows applications.

The homepage of MinGW states that

Code:

MinGW, being Minimalist, does not, and never will, attempt to provide a POSIX runtime environment for POSIX application deployment on MS-Windows.

Malkom · 04-24-2011, 02:26 PM

Thanks for the replies. However, I resolved this issue before I saw them. AlexCG was right -- the main() function needed argc and argv added. Apparently it looks for it under the name of SDL_main(), and so you need the arguments it expects.

MTK358 · 04-24-2011, 02:44 PM

Quote:

Originally Posted by Malkom

I resolved this issue

Then mark the thread as solved.

MrCode · 04-24-2011, 03:11 PM

Quote:

Originally Posted by MTK358

Is that like a Linux environment for Windows?

You want Cygwin.