genders_errnum() returns the error code stored in handle.
genders_strerror() returns a pointer to a string describing the error code errnum.
Generally, an error code is retrieved by genders_errnum() and then passed to genders_strerror().
genders_errormsg() returns a pointer to a string describing the error stored in handle. It is logically
equivalent to:
char *genders_strerror(genders_errnum(genders_t handle));
genders_perror() is similar to perror(3). It produces a message on standard error output, describing the
error stored in handle. If msg is not NULL, the string pointed to by msg, a colon, and a blank are
printed before the error message.