.\" gd_constants.3.  The gd_constants man page.
.\"
.\" Copyright (C) 2008, 2009, 2010 D. V. Wiebe
.\"
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.\" This file is part of the GetData project.
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.\" under the terms of the GNU Free Documentation License, Version 1.2 or
.\" any later version published by the Free Software Foundation; with no
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.TH gd_constants 3 "15 October 2010" "Version 0.7.0" "GETDATA"
.SH NAME
gd_constants \(em retrieve a list of constant values from a dirfile
.SH SYNOPSIS
.B #include <getdata.h>
.HP
.nh
.ad l
.BI "const void *gd_constants(DIRFILE *" dirfile ", gd_type_t
.IB return_type );
.hy
.ad n
.SH DESCRIPTION
The
.BR gd_constants ()
function queries a dirfile(5) database specified by
.I dirfile
and returns a read-only list of values of the all
.B CONST
type fields defined in the database after type conversion to the data type
specified by
.IR return_type .
Notably, this list does not include /META subfields.  For a list of valid
symbols to use for
.IR return_type ,
see the
.BR gd_get_constant (3)
man page.

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

The array returned will be de-allocated by a call to
.BR gd_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
.B CONST
fields returned by
.BR gd_field_list_by_type (3).
The array is unterminated.  The number of values in the array can be obtained
from a call to
.BR gd_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
.BR gd_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
de-allocated by a call to
.BR gd_close (3).

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

.SH RETURN VALUE
Upon successful completion,
.BR gd_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:
.TP 8
.B GD_E_ALLOC
The library was unable to allocate memory.
.TP
.B GD_E_BAD_DIRFILE
The supplied dirfile was invalid.
.TP
.B GD_E_BAD_TYPE
The
.I return_type
specified was invalid.
.PP
The dirfile error may be retrieved by calling
.BR gd_error (3).
A descriptive error string for the last error encountered can be obtained from
a call to
.BR gd_error_string (3).
.SH SEE ALSO
.BR dirfile (5),
.BR gd_open (3),
.BR gd_error (3),
.BR gd_error_string (3),
.BR gd_field_list_by_type (3),
.BR gd_get_constant (3),
.BR gd_nfields_by_type (3)