al_for_each_fs_entry - Allegro 5 API

       This  function takes the ALLEGRO_FS_ENTRY(3alleg5) dir, which should represent a directory, and looks for
       any other file system entries that are in it.   This  function  will  then  call  the  callback  function
       callback once for every filesystem entry in the directory dir.

       The callback callback must be of type int callback(ALLEGRO_FS_ENTRY * entry, void * extra).  The callback
       will  be called with a pointer to an ALLEGRO_FS_ENTRY(3alleg5) that matches one file or directory in dir,
       and the pointer passed in the extra parameter to al_for_each_fs_entry(3alleg5).

       When callback returns ALLEGRO_FOR_EACH_FS_ENTRY_STOP or ALLEGRO_FOR_EACH_FS_ENTRY_ERROR,  iteration  will
       stop immediately and al_for_each_fs_entry(3alleg5) will return the value the callback returned.

       When  callback  returns  ALLEGRO_FOR_EACH_FS_ENTRY_OK  iteration  will  continue  normally,  and  if  the
       ALLEGRO_FS_ENTRY(3alleg5) parameter of callback is a directory, al_for_each_fs_entry(3alleg5)  will  call
       itself on that directory.  Therefore the function will recusively descend into that directory.

       However,   when   callback   returns   ALLEGRO_FOR_EACH_FS_ENTRY_SKIP   iteration   will   continue,  but
       al_for_each_fs_entry(3alleg5) will NOT recurse into the ALLEGRO_FS_ENTRY(3alleg5) parameter  of  callback
       even if it is a directory.

       This  function  will skip any files or directories named . or .. which may exist on certain platforms and
       may signify the current and the parent  directory.   The  callback  will  not  be  called  for  files  or
       directories with such a name.

       Returns  ALLEGRO_FOR_EACH_FS_ENTRY_OK if successful, or ALLEGRO_FOR_EACH_FS_ENTRY_ERROR if something went
       wrong in processing the directory.  In that case it will use al_set_errno(3alleg5) to indicate  the  type
       of  error  which  occurred.   This  function returns ALLEGRO_FOR_EACH_FS_ENTRY_STOP in case iteration was
       stopped by making callback return that value.  In this case, al_set_errno(3alleg5) will not be used.

       al_for_each_fs_entry - Allegro 5 API

ALLEGRO_FOR_EACH_FS_ENTRY_RESULT(3alleg5)

       5.1.9

Allegro reference manual                                                           al_for_each_fs_entry(3alleg5)

              #include <allegro5/allegro.h>

              int al_for_each_fs_entry(ALLEGRO_FS_ENTRY *dir,
                                       int (*callback)(ALLEGRO_FS_ENTRY *dir, void *extra),
                                       void *extra)