Linux manual pages Section 3  

Name

getgrent_r, fgetgrent_r — get group file entry reentrantly

Synopsis

#include <grp.h>
int getgrent_r( struct group *gbuf,
  char *buf,
  size_t buflen,
  struct group **gbufp);
 
int fgetgrent_r( FILE *fp,
  struct group *gbuf,
  char *buf,
  size_t buflen,
  struct group **gbufp);
 
[Note] Note
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
getgrent_r():
_GNU_SOURCE
fgetgrent_r():
_SVID_SOURCE

DESCRIPTION

The functions getgrent_r() and fgetgrent_r() are the reentrant versions of getgrent(3) and fgetgrent(3). The former reads the next group entry from the stream initialized by setgrent(3). The latter reads the next group entry from the stream fp.

The group structure is defined in <grp.h> as follows:

struct group {
  char * gr_name;
/* group name */
  char * gr_passwd;
/* group password */
  gid_t   gr_gid;
/* group ID */
  char ** gr_mem;
/* group members */
};

The nonreentrant functions return a pointer to static storage, where this static storage contains further pointers to group name, password and members. The reentrant functions described here return all of that in caller-provided buffers. First of all there is the buffer gbuf that can hold a struct group. And next the buffer buf of size buflen that can hold additional strings. The result of these functions, the struct group read from the stream, is stored in the provided buffer *gbuf, and a pointer to this struct group is returned in *gbufp.

RETURN VALUE

On success, these functions return 0 and *gbufp is a pointer to the struct group. On error, these functions return an error value and *gbufp is NULL.

ERRORS

ENOENT

No more entries.

ERANGE

Insufficient buffer space supplied. Try again with larger buffer.

CONFORMING TO

These functions are GNU extensions, done in a style resembling the POSIX version of functions like getpwnam_r(3). Other systems use prototype

struct group *getgrent_r(struct group *grp, char *buf,
                         int buflen);

or, better,

int getgrent_r(struct group *grp, char *buf, int buflen,
               FILE **gr_fp);

NOTES

The function getgrent_r() is not really reentrant since it shares the reading position in the stream with all other threads.

EXAMPLE

#define _GNU_SOURCE
#include <grp.h>
#include <stdio.h>
#include <stdlib.h>
#define BUFLEN 4096

int
main(void)
{
    struct group grp, *grpp;
    char buf[BUFLEN];
    int i;

    setgrent();
    while (1) {
        i = getgrent_r(&grp, buf, BUFLEN, &grpp);
        if (i)
            break;
        printf("%s (%d):", grpp−>gr_name, grpp−>gr_gid);
        for (i = 0; ; i++) {
            if (grpp−>gr_mem[i] == NULL)
                break;
            printf(" %s", grpp−>gr_mem[i]);
        }
        printf("\n");
    }
    endgrent();
    exit(EXIT_SUCCESS);
}

SEE ALSO

fgetgrent(3), getgrent(3), getgrgid(3), getgrnam(3), putgrent(3), group(5)

COLOPHON

This page is part of release 3.24 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.


  Copyright (c) 2003 Andries Brouwer (aebcwi.nl)

This is free documentation; you can redistribute it and/or
modify it under the terms of the GNU General Public License as
published by the Free Software Foundation; either version 2 of
the License, or (at your option) any later version.

The GNU General Public License's references to "object code"
and "executables" are to be interpreted as the output of any
document formatting or typesetting system, including
intermediate and printed output.

This manual is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public
License along with this manual; if not, write to the Free
Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111,
USA.