gd_get_carray, gd_get_carray_slice, gd_get_constant—retrieve CONST or CARRAY data from a Dirfile database


#include <getdata.h>

int gd_get_carray_slice(DIRFILE *dirfile, const char *field_code, unsigned int start, size_t len, gd_type_t return_type, void *data_out);

int gd_get_carray(DIRFILE *dirfile, const char *field_code, gd_type_t return_type, void *data_out);

int gd_get_constant(DIRFILE *dirfile, const char *field_code, gd_type_t return_type, void *data_out);


The gd_get_carray_slice() function queries a dirfile(5) database specified by dirfile for the CONST or CARRAY scalar field_code, which may contain a representation suffix. The data in the field is converted to the data type specified by return_type, and stored in the user-supplied buffer data_out. The first element of the field stored is given by start, and the number of elements stored is given by len.

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

The dirfile argument must point to a valid DIRFILE object previously created by a call to gd_open(3). The argument 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 gd_get_carray() may be obtained by calling gd_array_len(3). Unlike gd_getdata(3), calling 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 return_type argument should be one of the following symbols, which indicates the desired return type of the data:

unsigned 8-bit integer
signed (two's complement) 8-bit integer
unsigned 16-bit integer
signed (two's complement) 16-bit integer
unsigned 32-bit integer
signed (two's complement) 32-bit integer
unsigned 64-bit integer
signed (two's complement) 64-bit integer
IEEE-754 standard 32-bit single precision floating point number
IEEE-754 standard 64-bit double precision floating point number
C99-conformant 64-bit single precision complex number
C99-conformant 128-bit double precision complex number
the null type: the database is queried as usual, but no data is returned. In this case, data_out is ignored and may be NULL.

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 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.


On success, gd_get_carray(), gd_get_carray_slice(), and gd_get_constant() return zero. On error, they return a negative-valued error code. Possible error codes are:

The library was unable to allocate memory.
The field specified by field_code was not found in the database.
An invalid dirfile was supplied.
The supplied field_code was not a CONST nor CARRAY.
An invalid return_type was specified.
A request for data beyond the end of the field was made.
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.

The error code is also stored in the DIRFILE object and may be retrieved after this function returns by calling gd_error(3). A descriptive error string for the error may be obtained by calling gd_error_string(3).


The get_constant() function appeared in GetData-0.4.0.

In GetData-0.7.0, this function was renamed to gd_get_constant(). In this release, the gd_get_carray() and gd_get_carray_slice() functions also appeared.

In GetData-0.10.0, the error return from these functions changed from −1 to a negative-valued error code.


gd_array_len(3), gd_carrays(3), gd_error(3), gd_error_string(3), gd_open(3), gd_put_carray_slice(3), dirfile(5)

Last updated on 25 December 2016 for GetData Version 0.10.0.