• 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 * fp , 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 ():
  
   _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 the stream
  fp .
  
  
  
  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;      /* group members */
  };
  

  
  
  The non-reentrant 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.

• CONFORMING TO
  
  These functions are GNU extensions, done in a style resembling the POSIX version of functions like getpwnam_r(3) . Other systems use 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);
  }
  

• SEE ALSO
  
  fgetgrent(3) , getgrent(3) , getgrgid(3) , getgrnam(3) , putgrent(3) , group(5)
• COLOPHON
  
  This page is part of release 3.19 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.

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