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 *stream, 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():
           Since glibc 2.19:
               _DEFAULT_SOURCE
           Glibc 2.19 and earlier:
               _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 stream.

       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;         /* NULL-terminated array of pointers
                                          to names of 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.

ATTRIBUTES

       For an explanation of the terms used in this section, see attributes(7).
       ┌───────────────┬───────────────┬─────────────────────────────┐
       │ Interface     │ Attribute     │ Value                       │
       ├───────────────┼───────────────┼─────────────────────────────┤
       │ getgrent_r()  │ Thread safety │ MT-Unsafe race:grent locale │
       ├───────────────┼───────────────┼─────────────────────────────┤
       │ fgetgrent_r() │ Thread safety │ MT-Safe                     │
       └───────────────┴───────────────┴─────────────────────────────┘

       In the above table, grent in race:grent signifies that if any of the  functions  setgrent(),  getgrent(),
       endgrent(), or getgrent_r() are used in parallel in different threads of a program, then data races could
       occur.

CONFORMING TO

       These  functions  are  GNU  extensions,  done  in  a style resembling the POSIX version of functions like
       getpwnam_r(3).  Other systems use the 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 5.05 of  the  Linux  man-pages  project.   A  description  of  the  project,
       information   about   reporting   bugs,   and   the  latest  version  of  this  page,  can  be  found  at
       https://www.kernel.org/doc/man-pages/.

GNU                                                2017-09-15                                      GETGRENT_R(3)