getgrent_r(3) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | CONFORMING TO | NOTES | EXAMPLES | 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 *restrict gbuf,
                      char *restrict buf, size_t buflen,
                      struct group **restrict gbufp);
       int fgetgrent_r(FILE *restrict stream, struct group *restrict gbuf,
                      char *restrict buf, size_t buflen,
                      struct group **restrict 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(3), getgrent(3), endgrent(3), 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.

EXAMPLES         top

       #define _GNU_SOURCE
       #include <grp.h>
       #include <stdio.h>
       #include <stdint.h>
       #include <stdlib.h>
       #define BUFLEN 4096

       int
       main(void)
       {
           struct group grp;
           struct group *grpp;
           char buf[BUFLEN];
           int i;

           setgrent();
           while (1) {
               i = getgrent_r(&grp, buf, sizeof(buf), &grpp);
               if (i)
                   break;
               printf("%s (%jd):", grpp->gr_name, (intmax_t) grpp->gr_gid);
               for (int j = 0; ; j++) {
                   if (grpp->gr_mem[j] == NULL)
                       break;
                   printf(" %s", grpp->gr_mem[j]);
               }
               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 5.13 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                            2021-03-22                  GETGRENT_R(3)

Pages that refer to this page: fgetgrent(3)getgrent(3)