get_constants (3) - Linux Manuals

get_constants: retrieve a list of constant values from a dirfile


get_constants --- retrieve a list of constant values from a dirfile


#include <getdata.h>
const void *get_constants(DIRFILE *dirfile, gd_type_t return_type);


The get_constants() function queries a dirfile(5) database specified by dirfile and returns a read-only list of values of the all CONST type fields defined in the database after type conversion to the data type specified by return_type. Notably, this list does not include /META subfields. For a list of valid symbols to use for return_type, see the getdata(3) man page.

The dirfile argument must point to a valid DIRFILE object previously created by a call to dirfile_open(3).

The array returned will be de-allocated by a call to dirfile_close(3) and should not be de-allocated by the caller. The list returned should not be assumed to be in any particular order, although it is guaranteed to be in the same order as the list of CONST fields returned by get_field_list_by_type(3). The array is unterminated. The number of values in the array can be obtained from a call to get_nfields_by_type(3).

The caller may not modify any values in the array, or the array itself. Doing so may cause database corruption. The pointer returned is guaranteed to be valid only until get_constants() is called again with the same arguments, or until the dirfile's metadata is modified (by adding, modifying or deleting an entry), or until the array is deallocated by a call to dirfile_close(3).

A corresponding list of names for these fields may be obtained by calling get_field_list_by_type(3).


Upon successful completion, get_constants() returns a pointer to an array of values containing the values of all the constants defined in the dirfile database. If no constants are defined in the database, NULL is returned. On error it returns NULL and sets the dirfile error to a non-zero error value. Possible error values are:
The library was unable to allocate memory.
The supplied dirfile was invalid.
The return_type specified was invalid. The dirfile error may be retrieved by calling get_error(3). A descriptive error string for the last error encountered can be obtained from a call to get_error_string(3).