NAME

       getgrent_r, fgetgrent_r - get group file entry reentrantly

SYNOPSIS

       #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

       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.

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.

EXAMPLES

       #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

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

COLOPHON

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       found at https://www.kernel.org/doc/man-pages/.