(libc.info.gz) Scanning All Groups

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 29.14.3 Scanning the List of All Groups
 ---------------------------------------
 
 This section explains how a program can read the list of all groups in
 the system, one group at a time.  The functions described here are
 declared in `grp.h'.
 
    You can use the `fgetgrent' function to read group entries from a
 particular file.
 
  -- Function: struct group * fgetgrent (FILE *STREAM)
      The `fgetgrent' function reads the next entry from STREAM.  It
      returns a pointer to the entry.  The structure is statically
      allocated and is overwritten on subsequent calls to `fgetgrent'.
      You must copy the contents of the structure if you wish to save the
      information.
 
      The stream must correspond to a file in the same format as the
      standard group database file.
 
  -- Function: int fgetgrent_r (FILE *STREAM, struct group *RESULT_BUF,
           char *BUFFER, size_t BUFLEN, struct group **RESULT)
      This function is similar to `fgetgrent' in that it reads the next
      user entry from STREAM.  But the result is returned in the
      structure pointed to by RESULT_BUF.  The first BUFLEN bytes of the
      additional buffer pointed to by BUFFER are used to contain
      additional information, normally strings which are pointed to by
      the elements of the result structure.
 
      This stream must correspond to a file in the same format as the
      standard group database file.
 
      If the function returns zero RESULT points to the structure with
      the wanted data (normally this is in RESULT_BUF).  If errors
      occurred the return value is non-zero and RESULT contains a null
      pointer.
 
    The way to scan all the entries in the group database is with
 `setgrent', `getgrent', and `endgrent'.
 
  -- Function: void setgrent (void)
      This function initializes a stream for reading from the group data
      base.  You use this stream by calling `getgrent' or `getgrent_r'.
 
  -- Function: struct group * getgrent (void)
      The `getgrent' function reads the next entry from the stream
      initialized by `setgrent'.  It returns a pointer to the entry.  The
      structure is statically allocated and is overwritten on subsequent
      calls to `getgrent'.  You must copy the contents of the structure
      if you wish to save the information.
 
  -- Function: int getgrent_r (struct group *RESULT_BUF, char *BUFFER,
           size_t BUFLEN, struct group **RESULT)
      This function is similar to `getgrent' in that it returns the next
      entry from the stream initialized by `setgrent'.  Like
      `fgetgrent_r', it places the result in user-supplied buffers
      pointed to RESULT_BUF and BUFFER.
 
      If the function returns zero RESULT contains a pointer to the data
      (normally equal to RESULT_BUF).  If errors occurred the return
      value is non-zero and RESULT contains a null pointer.
 
  -- Function: void endgrent (void)
      This function closes the internal stream used by `getgrent' or
      `getgrent_r'.
 

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