Returns true if the filename is relative. allegro game programming library.
#include <allegro.h>
int is_relative_filename(const char *filename);
Returns TRUE if the filename is relative or FALSE if it is absolute. Note that an absolute filename under DOS (with a device separator) will be considered as relative under Unix, because there absolute paths always start with a slash.
make_absolute_filename(3alleg4), make_relative_filename(3alleg4)