getgrent_r(3) — Linux manual page

getgrent_r(3)           Library Functions Manual           getgrent_r(3)

NAME

       getgrent_r, fgetgrent_r - get group file entry reentrantly

LIBRARY

       Standard C library (libc, -lc)

SYNOPSIS

       #include <grp.h>

       int getgrent_r(struct group *restrict gbuf,
                      char buf[restrict .buflen], size_t buflen,
                      struct group **restrict gbufp);
       int fgetgrent_r(FILE *restrict stream, struct group *restrict gbuf,
                      char buf[restrict .buflen], 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

       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(3), getgrent(3), endgrent(3), or
       getgrent_r() are used in parallel in different threads of a
       program, then data races could occur.

VERSIONS

       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);

STANDARDS

       GNU.

HISTORY

       These functions are done in a style resembling the POSIX version
       of functions like getpwnam_r(3).

NOTES

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

EXAMPLES

       #define _GNU_SOURCE
       #include <grp.h>
       #include <stdint.h>
       #include <stdio.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 (size_t j = 0; ; j++) {
                   if (grpp->gr_mem[j] == NULL)
                       break;
                   printf(" %s", grpp->gr_mem[j]);
               }
               printf("\n");
           }
           endgrent();
           exit(EXIT_SUCCESS);
       }

SEE ALSO

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

COLOPHON

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Linux man-pages 6.9.1          2024-06-15                  getgrent_r(3)

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

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