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/.

GNU                                                2010-10-21                                      GETGRENT_R(3)