.\" gd_frameoffset.3.  The gd_frameoffset man page.
.\"
.\" Copyright (C) 2008, 2010 D. V. Wiebe
.\"
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.TH gd_frameoffset 3 "15 July 2010" "Version 0.7.0" "GETDATA"
.SH NAME
gd_frameoffset \(em report the starting frame of fields in a dirfile
.SH SYNOPSIS
.B #include <getdata.h>
.HP
.nh
.ad l
.BI "off_t gd_frameoffset(DIRFILE *" dirfile ", int " fragment_index );
.hy
.ad n
.SH DESCRIPTION
The
.BR gd_frameoffset ()
function queries a dirfile(5) database specified by
.I dirfile
and returns the frame offset (see dirfile-format(5)) for the fragment indexed by
.IR fragment_index .
The frame offset of a fragment indicate the frame number of the first sample
of data stored in binary files associated with
.B RAW
fields defined in the specified fragment.  The frame offset of a fragment
containing no
.B RAW
fields is ignored.

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

.SH RETURN VALUE
Upon successful completion,
.BR gd_frameoffset ()
returns the frame offset of the specified fragment.  On error, it
returns -1 and sets the dirfile error to a non-zero error value.  Possible error
values are:
.TP 8
.B GD_E_BAD_DIRFILE
The supplied dirfile was invalid.
.TP
.B GD_E_BAD_INDEX
The supplied index was out of range.
.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 gd_alter_frameoffset (3),
.BR gd_open (3),
.BR gd_error (3),
.BR gd_error_string (3),
.BR dirfile (5),
.BR dirfile-format (5)