Gd_get_constant retrieve a scalar constant from a dirfile database
#include <getdata.h> int gd_get_constant(DIRFILE *dirfile, const char *field_code, gd_type_t return_type, void *data_out);
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.
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).