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GETGRENT_R(3)              Linux Programmer's Manual             GETGRENT_R(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);

   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  non-reentrant  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 getpw-
       nam_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 3.22 of the Linux man-pages project.  A description of the project, and informa-
       tion about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



GNU                               2007-07-26                     GETGRENT_R(3)