gd_get_constant(3)

NAME
gd_get_constant — retrieve a scalar constant from a dirfile database

SYNOPSIS
#include <getdata.h>

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

DESCRIPTION
The gd_get_constant() function queries a dirfile(5) database specified by dirfile for the CONST scalar field_code, which may contain a representation suffix. The constant is converted to the data type specified by return_type, and stored in the user-supplied buffer data_out. 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 a value of the return type specified. The return_type argument should be one of the following symbols, which indicates the desired return type of the data:

    GD_UINT8
        unsigned 8-bit integer

    GD_INT8
        signed (two's complement) 8-bit integer

    GD_UINT16
        unsigned 16-bit integer

    GD_INT16
        signed (two's complement) 16-bit integer

    GD_UINT32
        unsigned 32-bit integer

    GD_INT32
        signed (two's complement) 32-bit integer

    GD_UINT64
        unsigned 64-bit integer

    GD_INT64
        signed (two's complement) 64-bit integer

    GD_FLOAT32
        IEEE-754 standard 32-bit single precision floating point number

    GD_FLOAT64
        IEEE-754 standard 64-bit double precision floating point number

    GD_COMPLEX64
        C99-conformant 64-bit single precision complex number

    GD_COMPLEX128
        C99-conformant 128-bit double precision complex number

    GD_NULL
        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 constant 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.

RETURN VALUE
On success, gd_get_constant() returns zero. On error, it returns -1 and sets the dirfile error to a non-zero value. Possible error values are:

GD_E_BAD_CODE
    The field specified by field_code was not found in the database.

GD_E_BAD_DIRFILE
    An invalid dirfile was supplied.

GD_E_BAD_FIELD_TYPE
    The supplied field_code referred to a field of a type other than CONST. The caller should use gd_getdata(3), or gd_get_string(3) instead.

GD_E_BAD_REPR
    The representation suffix specified in fieldcode, or in one of the field codes it uses for input, was invalid.

GD_E_BAD_TYPE
    An invalid return_type was specified.

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.

The dirfile error may be retrieved by calling gd_error(3). A descriptive error string for the last error encountered may be obtained from a call to gd_error_string(3).

SEE ALSO
dirfile(5), gd_open(3), gd_error(3), gd_error_string(3), gd_get_carray(3), gd_constants(3), gd_put_constant(3)