.\" gd_get_carray_slice.3.  The gd_get_carray_slice man page.
.\"
.\" Copyright (C) 2010-2013 D. V. Wiebe
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.TH gd_get_carray_slice 3 "1 October 2013" "Version 0.9.0" "GETDATA"
.SH NAME
gd_get_carray, gd_get_carray_slice, gd_get_constant \(em retrieve CONST or CARRAY data from a dirfile database
.SH SYNOPSIS
.B #include <getdata.h>
.HP
.nh
.ad l
.BI "int gd_get_carray_slice(DIRFILE *" dirfile ", const char *" field_code ,
.BI "unsigned int " start ", size_t " len ", gd_type_t " return_type ,
.BI "void *" data_out );
.HP
.BI "int gd_get_carray(DIRFILE *" dirfile ", const char *" field_code ,
.BI "gd_type_t " return_type ", void *" data_out );
.HP
.BI "int gd_get_constant(DIRFILE *" dirfile ", const char *" field_code ,
.BI "gd_type_t " return_type ", void *" data_out );
.hy
.ad n
.SH DESCRIPTION
The
.BR gd_get_carray_slice ()
function queries a dirfile(5) database specified by
.I dirfile
for the
.B CONST
or
.B CARRAY
scalar array
.IR field_code ,
which may contain a representation suffix.
The data in the field is converted to the data type specified by
.IR return_type ,
and stored in the user-supplied buffer
.IR data_out .
The first element of the field stored is given by
.IR start ,
and the number of elements stored is given by
.IR len .

The
.BR gd_get_carray ()
function behaves similarly, except it returns the entire field, as if
.BR gd_get_carray_slice ()
were called with
.I start
equal to zero and
.I len
equal to the value returned by
.BR gd_carray_len (3).
The
.BR gd_get_constant ()
function is equivalent to calling
.BR gd_get_carray_slice ()
with
.I start
equal to zero and
.I len
equal to one.

The 
.I dirfile
argument must point to a valid DIRFILE object previously created by a call to
.BR gd_open (3).
The argument
.I data_out
must point to a valid memory location of sufficient size to hold all the
requested data of the return type specified.  The number of elements returned
by
.BR gd_get_carray ()
may be obtained by calling
.BR gd_carray_len (3).
Unlike
.BR gd_getdata (3),
calling
.BR gd_get_carray_slice ()
never results in a short read; attempting to read past the end of the
field will result in an error, and no data will be returned.

The 
.I return_type
argument should be one of the following symbols, which indicates the desired
return type of the data:
.RS
.TP 11
.B GD_UINT8
unsigned 8-bit integer
.TP
.B GD_INT8
signed (two's complement) 8-bit integer
.TP
.B GD_UINT16
unsigned 16-bit integer
.TP
.B GD_INT16
signed (two's complement) 16-bit integer
.TP
.B GD_UINT32
unsigned 32-bit integer
.TP
.B GD_INT32
signed (two's complement) 32-bit integer
.TP
.B GD_UINT64
unsigned 64-bit integer
.TP
.B GD_INT64
signed (two's complement) 64-bit integer
.TP
.B GD_FLOAT32
IEEE-754 standard 32-bit single precision floating point number
.TP
.B GD_FLOAT64
IEEE-754 standard 64-bit double precision floating point number
.TP
.B GD_COMPLEX64
C99-conformant 64-bit single precision complex number
.TP
.B GD_COMPLEX128
C99-conformant 128-bit double precision complex number
.TP
.B GD_NULL
the null type: the database is queried as usual, but no data is returned.
In this case,
.I data_out
is ignored and may be NULL.
.RE

The return type of the field need not be the same as the type of the data stored
in the database.  Type conversion will be performed as necessary to return the
requested type.  If the
.I field_code
does not indicate a representation, but conversion from a complex value to a
purely real one is required, only the real portion of the requested vector will
be returned.
.SH RETURN VALUE
On success,
.BR gd_get_carray (),
.BR gd_get_carray_slice (),
and
.BR gd_get_constant ()
return zero.  On error, they return -1 and set the dirfile error to a non-zero
value.  Possible error values are:
.TP 8
.B GD_E_ALLOC
The library was unable to allocate memory.
.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
was not a
.BR CONST
nor
.BR CARRAY .
The caller should use
.BR gd_getdata (3)
or
.BR gd_get_string (3)
instead.
.TP
.B GD_E_BAD_TYPE
An invalid
.I return_type
was specified.
.TP
.B GD_E_BOUNDS
A request for data beyond the end of the field was made.
.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.
.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_carray_len (3),
.BR gd_carrays (3),
.BR gd_error (3),
.BR gd_error_string (3),
.BR gd_get_constant (3),
.BR gd_open (3),
.BR gd_put_carray_slice (3)