evert@localhost ~/C++/allegro $ g++ units.cpp main.cpp `allegro-config --cflags --static` -o risk
units.cpp:15:2: warning: no newline at end of file
/tmp/cc4G8GlX.o: In function `unit::is_selected()':
units.cpp:(.text+0x1f): undefined reference to `buffer'
collect2: ld returned 1 exit status