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

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).

     allbox; lb lb lbw27 l l l.  Interface Attribute Value  T{  getgrent_r()
     T}   Thread   safety MT-Unsafe   race:grent   locale  T{  fgetgrent_r()
     T}   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); }