NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | CONFORMING TO | NOTES | EXAMPLE | SEE ALSO | COLOPHON

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

NAME         top

       getgrent_r, fgetgrent_r - get group file entry reentrantly

SYNOPSIS         top

       #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         top

       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         top

       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         top

       ENOENT No more entries.

       ERANGE Insufficient buffer space supplied.  Try again with larger
              buffer.

ATTRIBUTES         top

       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         top

       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         top

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

EXAMPLE         top

       #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         top

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

COLOPHON         top

       This page is part of release 4.07 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                              2016-03-15                    GETGRENT_R(3)