Allegro in Ubuntu: undefined reference to `al_inst

Question

I tried installing the Allegro library today. I have same experience in C++, but it seems I have none in doing stuff like that. I have compiled Allegro 5.0 from source and put it in /usr/lib/gcc/i486-linux-gnu/4.4/include/allegro5. But when I try to compile my code, this comes up:

    > g++ test2.cc -o test2
/home/chris/Desktop/c++/test2/.objs/main.o||In function `main':|
main.cpp:(.text+0x22)||undefined reference to `al_install_system'|
main.cpp:(.text+0x3e)||undefined reference to `al_create_display'|
main.cpp:(.text+0x6b)||undefined reference to `al_map_rgb'|
main.cpp:(.text+0x8e)||undefined reference to `al_clear_to_color'|
main.cpp:(.text+0x93)||undefined reference to `al_flip_display'|
main.cpp:(.text+0xa1)||undefined reference to `al_rest'|
main.cpp:(.text+0xa9)||undefined reference to `al_destroy_display'|
||=== Build finished: 7 errors, 0 warnings ===|

The code I am using:

#include <stdio.h>
#include <allegro5/allegro.h>

int main(int argc, char **argv)
{
   ALLEGRO_DISPLAY *display = NULL;

   if(!al_init()) {
      fprintf(stderr, "failed to initialize allegro!\n");
      return -1;
   }

   display = al_create_display(640, 480);
   if(!display) {
      fprintf(stderr, "failed to create display!\n");
      return -1;
   }

   al_clear_to_color(al_map_rgb(0,0,0));
   al_flip_display();
   al_rest(10.0);
   al_destroy_display(display);
   return 0;
}

allegro-config --libs returns nothing. I had Allegro as package first, but it didn'T work either.

Answer 1

Allegro 5 uses pkg-config.

gcc foo.c -o foo $(pkg-config --libs allegro-5.0)

You will also need to specify addon libraries that you use:

gcc foo.c -o foo $(pkg-config --libs allegro-5.0 allegro_image-5.0)

Answer 2

You need to link with the Allegro libraries, but you don't seem to do so.

allegro-config --libs returns nothing.

There's part of your problem. Normally, you should be able to add it to your command line, like so:

g++ `allegro-config --libs` test2.cc -o test2

On my system (Ubuntu 10.10) it gives this:

$ allegro-config --libs
-L/usr/lib -Wl,-Bsymbolic-functions -lalleg-4.2.2

Are you invoking the right allegro-config? Maybe you should specify the full path to it?