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);

   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 */
           };

       For more information about the fields of this structure, see group(5).

       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 3.54 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/.