al_ustr_appendf - Allegro 5 API

       This  function  appends  formatted  output  to  the string us.  fmt is a printf-style format string.  See
       al_ustr_newf(3alleg5) about the “%s” and “%c” specifiers.

       Returns true on success, false on error.

       al_ustr_appendf - Allegro 5 API

al_ustr_vappendf(3alleg5), al_ustr_append(3alleg5)

Allegro reference manual                                                                al_ustr_appendf(3alleg5)

              #include <allegro5/allegro.h>

              bool al_ustr_appendf(ALLEGRO_USTR *us, const char *fmt, ...)