It didn't save the bitmaps for me at all until I put a al_init_image_addon() right after al_init(). Oh, yeah, there is no "init_allegro()" unless you didn't post a function you wrote yourself, but you must have or it wouldn't have compiled. I used "al_init()".

Anyway, it now shows a blank screen, which turns to red, and both bitmap files are green.

I'm using Allegro 5.1.7 with Linux, Nvidia GeForce GTX 650.

What tests? The Allegro examples? They all worked, except the ones for hardware I don't have (such as dual monitors). There was also some resizing thing that didn't work right a couple of years ago, I don't think it's fixed yet.

I don't think I tried them all because it's so tedious, there were a couple of GLSL examples I just ran a few days ago and I'm pretty sure I'd never seen them before (they worked correctly too).

[EDIT]
I always get rid of the noveau (?) open source driver and install the Nvidia proprietary driver because the noveau driver sucks so hard, for example, the ex_gldepth example doesn't work right with it. OTOH, about a year ago I reported a problem and spent about three days trying to fix it when I saw a new Nvidia driver had come out and it worked correctly then. Shit happens.

I didn't try those, I just fiddled with it for two minutes and tried about five of them (including test_bitmap.ini) and they all flashed a window too fast to really see what's happening and the console is full of OK messages.

pepsi@fractal:/home/prog/allegro-5.1.7/build/tests 05:45 AM $ test_driver ../../tests/test_backbuffer.ini 
OK   test bbsrc [sw]
OK   test bbsrc [hw]
OK   test bbsrc translate [sw]
OK   test bbsrc translate [hw]
OK   test bbsrc outside [sw]
OK   test bbsrc outside [hw]
OK   test bbsrc tint [sw]
OK   test bbsrc tint [hw]

total tests:  8
passed tests: 8
failed tests: 0

Kyborg, what video card and driver do you have?

If it's Nvidia I'm using NVIDIA-Linux-x86_64-331.20.run installer for 64 bit linux.

This part of the code is fine :

int main(void) { 
 al_init();
 al_init_image_addon();
 ALLEGRO_DISPLAY* display = al_create_display(800, 600);
 al_clear_to_color(al_map_rgb(0, 0, 0));
 al_flip_display();

The next part flips the display without drawing anything to it (which means it could display anything) (you never set the drawing target back to the backbuffer) :

 ALLEGRO_BITMAP* bitmap = al_create_bitmap(160, 80);
 al_set_target_bitmap(bitmap);
 al_clear_to_color(al_map_rgb(0, 100, 0));
 al_save_bitmap("green.png", bitmap); //green.png is green
 al_flip_display(); //display could hold anything
 cin.get();

green.png should now exist and be green.

The last part of the code you showed us should save red.png as a green bitmap as well, because the green bitmap is the bitmap you specified to save :

 al_set_target_backbuffer(display);
 al_clear_to_color(al_map_rgb(100, 0, 0));
 al_save_bitmap("red.png", bitmap); //red.png is green b/c bitmap is green
 al_flip_display(); //display is now red
 cin.get(); return 0; }

The screen should be red now.