al_append_native_text_log man page
al_append_native_text_log — Allegro 5 API
#include <allegro5/allegro_native_dialog.h> void al_append_native_text_log(ALLEGRO_TEXTLOG *textlog, char const *format, ...)
Appends a line of text to the message log window and scrolls to the bottom (if the line would not be visible otherwise). This works like printf. A line is continued until you add a newline character.
If the window is NULL then this function will fall back to calling printf. This makes it convenient to support logging to a window or a terminal.