.\" gd_put_constant.3.  The gd_put_constant man page.
.\"
.\" Copyright (C) 2008, 2009, 2010 D. V. Wiebe
.\"
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.TH gd_put_constant 3 "4 November 2010" "Version 0.7.0" "GETDATA"
.SH NAME
gd_put_constant \(em retrieve a scalar constant from a dirfile database
.SH SYNOPSIS
.B #include <getdata.h>
.HP
.nh
.ad l
.BI "int gd_put_constant(DIRFILE *" dirfile ", const char *" field_code ,
.BI "gd_type_t " data_type ", const void *" data_in );
.hy
.ad n
.SH DESCRIPTION
The
.BR gd_put_constant ()
function queries a dirfile(5) database specified by
.I dirfile
and sets the
.B CONST
scalar
.I field_code ,
which may not contain a representation suffix, to the value specified in
.IR data_in ,
which should be of the type indicated by
.IR data_type .

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

The 
.I data_type
argument should be one of the following symbols, which indicates the desired
return type of the data:
.RS
.TP 11
.I GD_UINT8
unsigned 8-bit integer
.TP
.I GD_INT8
signed (two's complement) 8-bit integer
.TP
.I GD_UINT16
unsigned 16-bit integer
.TP
.I GD_INT16
signed (two's complement) 16-bit integer
.TP
.I GD_UINT32
unsigned 32-bit integer
.TP
.I GD_INT32
signed (two's complement) 32-bit integer
.TP
.I GD_UINT64
unsigned 64-bit integer
.TP
.I GD_INT64
signed (two's complement) 64-bit integer
.TP
.IR GD_FLOAT32 \~or\~ GD_FLOAT
IEEE-754 standard 32-bit single precision floating point number
.TP
.IR GD_FLOAT64 \~or\~ GD_DOUBLE
IEEE-754 standard 64-bit double precision floating point number
.RE

The data type of the supplied value need not be the same as the type of the 
storage type of the constant in the database.  Type conversion will be performed
as necessary to return the requested type.  The argument
.I data_out
must point to valid data type of the specified type.

Because constant values are stored in the dirfile metadata, the new value of
.I field_code
won't be written to disk until the dirfile metadata is flushed with
.BR gd_metaflush (3),
or until the dirfile is closed.
.SH RETURN VALUE
On success,
.BR gd_put_constant ()
returns zero.  On error, it returns -1 and sets the dirfile error to a non-zero
value.  Possible error values are:
.TP 8
.B GD_E_ACCMODE
The specified
.I dirfile
was opened read-only.
.TP
.B GD_E_BAD_CODE
The field specified by
.I field_code
was not found in the database.
.TP
.B GD_E_BAD_DIRFILE
An invalid
.I dirfile
was supplied.
.TP
.B GD_E_BAD_FIELD_TYPE
The supplied
.I field_code
referred to a field of type other than
.BR CONST .
The caller should use
.BR gd_putdata "(3), " gd_put_carray (3),
or
.BR gd_put_string (3)
instead.
.TP
.B GD_E_BAD_REPR
The representation suffix specified in
.I field_code
was not recognised.
.TP
.B GD_E_BAD_TYPE
An invalid
.I data_type
was specified.
.TP
.B GD_E_INTERNAL_ERROR
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
maintainer.
.TP
.B GD_E_PROTECTED
The fragment containing the constant was protected from change.
.PP
The dirfile error may be retrieved by calling
.BR gd_error (3).
A descriptive error string for the last error encountered may be obtained from
a call to
.BR gd_error_string (3).
.SH SEE ALSO
.BR dirfile (5),
.BR gd_metaflush (3),
.BR gd_get_constant (3),
.BR gd_error (3),
.BR gd_error_string (3),
.BR gd_open (3),
.BR gd_put_carray (3),
.BR gd_put_string (3),
.BR gd_putdata (3)