gd_reference man page
gd_reference — retrieve or set the reference field for a Dirfile
const char *gd_reference(DIRFILE *dirfile, const char *field_code);
The gd_reference() function sets or retrieves the reference field (see dirfile(5)) associated with the dirfile specified by dirfile. If the field_code argument is non-NULL, the reference field for the dirfile will be set to the field specified. If field_code is NULL, the reference field is not modified. The field code should refer to a RAW field, and may not contain a representation suffix.
On success, gd_reference() returns the field code of the dirfile's reference field, which will be field_code, if field_code is non-NULL. If no RAW fields are defined in the dirfile, this function will return NULL, without raising an error. On error, NULL is returned and the dirfile error is set to a non-zero error value. Possible error values are:
The specified dirfile was opened read-only.
The library was unable to allocate memory.
The field specified by field_code was not found.
The supplied dirfile was invalid.
The field specified by field_code was not a RAW field.
The metadata of the primary format specification fragment (the file named format in the root dirfile directory) was protected from change.
The dirfile error may be retrieved by calling gd_error(3). A descriptive error string for the last error encountered can be obtained from a call to gd_error_string(3).
The get_reference() function appeared in GetData-0.4.2. It took only one parameter (the DIRFILE), and returned the current reference field.
The dirfile_reference() function appeared in GetData-0.5.0.
In GetData-0.7.0, the dirfile_reference() function was renamed to gd_reference() and the get_reference() function was removed.
gd_error(3), gd_error_string(3), gd_metaflush(3), gd_open(3), dirfile(5), dirfile-format(5)