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[EDIT] FILE: cookie_io_functions_t.h

/* Copyright (C) 1991-2018 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <http://www.gnu.org/licenses/>.  */

#ifndef __cookie_io_functions_t_defined
#define __cookie_io_functions_t_defined 1

#include <bits/types.h>

/* Functions to do I/O and file management for a stream.  */

/* Read NBYTES bytes from COOKIE into a buffer pointed to by BUF.
   Return number of bytes read.  */
typedef __ssize_t cookie_read_function_t (void *__cookie, char *__buf,
                                          size_t __nbytes);

/* Write NBYTES bytes pointed to by BUF to COOKIE.  Write all NBYTES bytes
   unless there is an error.  Return number of bytes written.  If
   there is an error, return 0 and do not write anything.  If the file
   has been opened for append (__mode.__append set), then set the file
   pointer to the end of the file and then do the write; if not, just
   write at the current file pointer.  */
typedef __ssize_t cookie_write_function_t (void *__cookie, const char *__buf,
                                           size_t __nbytes);

/* Move COOKIE's file position to *POS bytes from the
   beginning of the file (if W is SEEK_SET),
   the current position (if W is SEEK_CUR),
   or the end of the file (if W is SEEK_END).
   Set *POS to the new file position.
   Returns zero if successful, nonzero if not.  */
typedef int cookie_seek_function_t (void *__cookie, __off64_t *__pos, int __w);

/* Close COOKIE.  */
typedef int cookie_close_function_t (void *__cookie);

/* The structure with the cookie function pointers.
   The tag name of this struct is _IO_cookie_io_functions_t to
   preserve historic C++ mangled names for functions taking
   cookie_io_functions_t arguments.  That name should not be used in
   new code.  */
typedef struct _IO_cookie_io_functions_t
{
  cookie_read_function_t *read;		/* Read bytes.  */
  cookie_write_function_t *write;	/* Write bytes.  */
  cookie_seek_function_t *seek;		/* Seek/tell file position.  */
  cookie_close_function_t *close;	/* Close file.  */
} cookie_io_functions_t;

#endif

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