gd_get_string—retrieve STRING or SARRAY data from a Dirfile database


#include <getdata.h>

size_t gd_get_string(DIRFILE *dirfile, const char *field_code, size_t len, char *data_out);


The gd_get_string() function queries a dirfile(5) database specified by dirfile for the string scalar field_code, which should not contain a representation suffix. The first len characters of the string scalar are stored in the user-supplied buffer data_out. If field_code refers to a SARRAY field, the first element is returned.

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

If len equals zero, or if data_out equals NULL, no data will be copied to data_out, but the length of the string scalar will still be returned by gd_get_string(). Otherwise, the argument data_out must point to a valid memory location of sufficient size to hold at least len characters. If the length of the string scalar is greater than len, data_out will not be NUL-terminated.

The gd_get_sarray(3) function provides another way of retrieving STRING data, but without having to know the length of the returned string in advance. The code:

size_t len = gd_get_string(dirfile, field_code, 0, NULL);
char *string = malloc(len);
gd_get_string(dirfile, field_code, len, string);

which ensures the whole string, including the terminating NUL, is returned, can be replaced with, simply:

const char *string;
gd_get_sarray(dirfile, field_code, &string);

with the added benefit of not having manage the memory for the string.


On success, gd_get_string() returns the actual length of the specified string scalar, including space for the trailing NUL-character. A return value greater than len indicates that the output string is not NUL-terminated.

On error, this function returns 0 and stores a negative-valued error code in the DIRFILE object which may be retrieved by a subsequent call to gd_error(3). Possible error codes are:

The field specified by field_code was not found in the database.
An invalid dirfile was supplied.
The supplied field_code referred to a field of type other than STRING or SARRAY.
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.

A descriptive error string for the error may be obtained by calling gd_error_string(3).


The get_string() function appeared in GetData-0.4.0.

In GetData-0.7.0, this function was renamed to gd_get_string().


gd_get_sarray(3), gd_error(3), gd_error_string(3), gd_open(3), gd_put_string(3), dirfile(5)

Last updated on 25 December 2016 for GetData Version 0.10.0.