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gd_constants, gd_mconstants — retrieve a list of constant values from a Dirfile


#include <getdata.h>

const void *gd_constants(DIRFILE *dirfile, gd_type_t return_type);

const void *gd_mconstants(DIRFILE *dirfile, const char *parent, gd_type_t return_type);


The gd_constants() function queries a dirfile(5) database specified by dirfile and compiles a list of values of the all CONST fields defined in the database, excluding meta subfields. The values returned are converted to the data type specified by return_type. The return_type should be one of the following symbols:


See gd_get_constant(3) for the meaning of these symbols. The dirfile argument must point to a valid DIRFILE object previously created by a call to gd_open(3).

The gd_mconstants() function returns the same list for CONST meta subfields of the parent field specified by parent.

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


Upon successful completion, gd_constants() returns a pointer to an array containing the values of all the constants defined in the dirfile database. Similarly, gd_mconstants() returns a pointer to an array containing the values of the all the meta subfield constants of the specified parent field.

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 gd_field_list_by_type(3) or gd_mfield_list_by_type(3). The array is unterminated. The number of values in the array can be obtained from a call to gd_nfields_by_type(3) or gd_nmfields_by_type(3), as appropriate.

Memory for the returned array is managed by GetData and should not be de-allocated by the caller. The caller may not modify any values in the array. Doing so may cause database corruption. The pointer returned is guaranteed to be valid only until the function is called again, with the exception that, since each top-level field maintains its own arrays, calling gd_mconstants() for a one parent field does not invalidate the pointer returned for a any other parent.

Modifying the dirfile’s metadata invalidates any pointer returned by these functions. And no pointers remain valid after the dirfile is de-allocated by a call to gd_close(3) or gd_discard(3). Once a pointer is invalidated, the caller should not dereference it.

If no constants of the appropriate class are defined in the database, NULL is returned. This is not considered an error.

On error, these functions return NULL and store a negative-valued error code in the DIRFILE object which may be retrieved by a subsequent call to gd_error(3). Possible error codes are:

The library was unable to allocate memory.


The specified parent field code was not found, or referred to a metafield (gd_mconstants() only).


The supplied dirfile was invalid.


The return_type specified was not one of the symbols listed above.


An internal error occurred in the library while trying to perform the task. This indicates a bug in the library. Please report the incident to the GetData developers.

A descriptive error string for the error may be obtained by calling gd_error_string(3).


The functions get_constants() and get_mconstants() appeared in GetData-0.4.0.

In GetData-0.7.0, these functions were renamed to gd_constants() and gd_mconstants().


gd_error(3), gd_error_string(3), gd_field_list_by_type(3), gd_get_constant(3), gd_mfield_list_by_type(3), gd_nfields_by_type(3), gd_nmfields_by_type(3), gd_open(3), dirfile(5)