stdio/glue.c

   1 /* Copyright (C) 1991, 1992, 1996, 1997 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Library General Public License as
   6    published by the Free Software Foundation; either version 2 of the
   7    License, or (at your option) any later version.
   8
   9    The GNU C Library is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12    Library General Public License for more details.
  13
  14    You should have received a copy of the GNU Library General Public
  15    License along with the GNU C Library; see the file COPYING.LIB.  If not,
  16    write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  17    Boston, MA 02111-1307, USA.  */
  18
  19 /* This file provides glue between Unix stdio and GNU stdio.
  20    It supports use of Unix stdio `getc' and `putc' (and, by extension,
  21    `getchar' and `putchar') macros on GNU stdio streams (they are slow, but
  22    they work).  It also supports all stdio operations (including Unix
  23    `getc' and `putc') on Unix's stdin, stdout, and stderr (the elements of
  24    `_iob').
  25
  26    The reasoning behind this is to allow programs (and especially
  27    libraries) compiled with Unix header files to work with the GNU C
  28    library.  */
  29
  30 #include <stdio.h>
  31 #include <errno.h>
  32
  33 typedef union
  34   {
  35     struct
  36       {
  37         int magic;
  38         FILE **streamp;         /* Overlaps GNU stdio `bufp' member.  */
  39         /* These two overlap the GNU stdio `get_limit' and `put_limit'
  40            members.  They must be <= `streamp'/`bufp' for GNU getc and putc
  41            to do the right thing.  */
  42         FILE **streamp2, **streamp3;
  43       } glue;
  44     struct _iobuf
  45       {
  46         int _cnt;
  47         unsigned char *_ptr;
  48         unsigned char *_base;
  49         int _bufsiz;
  50         short int _flag;
  51         char _file;
  52       } unix_iobuf;
  53     FILE gnu_stream;
  54   } unix_FILE;
  55
  56 /* These are the Unix stdio's stdin, stdout, and stderr.
  57    In Unix stdin is (&_iob[0]), stdout is (&_iob[1]), and stderr is
  58    (&_iob[2]).  The magic number marks these as glued streams.  The
  59    __validfp macro in stdio.h is used by every stdio function.  It checks
  60    for glued streams, and replaces them with the GNU stdio stream.  */
  61 unix_FILE _iob[] =
  62   {
  63 #define S(name) { { _GLUEMAGIC, &name, &name, &name } }
  64     S (stdin),
  65     S (stdout),
  66     S (stderr),
  67 #undef  S
  68   };
  69
  70 /* Called by the Unix stdio `getc' macro.
  71    The macro is assumed to look something like:
  72        (--file->_cnt < 0 ? _filbuf (file) ...)
  73    In a Unix stdio FILE `_cnt' is the first element.
  74    In a GNU stdio or glued FILE, the first element is the magic number.  */
  75 int
  76 _filbuf (unix_FILE *file)
  77 {
  78   switch (++file->glue.magic)   /* Compensate for Unix getc's decrement.  */
  79     {
  80     case _GLUEMAGIC:
  81       /* This is a glued stream.  */
  82       return getc (*file->glue.streamp);
  83
  84     case  _IOMAGIC:
  85       /* This is a normal GNU stdio stream.  */
  86       return getc ((FILE *) file);
  87
  88     default:
  89       /* Bogus stream.  */
  90       __set_errno (EINVAL);
  91       return EOF;
  92     }
  93 }
  94
  95 /* Called by the Unix stdio `putc' macro.  Much like getc, above.  */
  96 int
  97 _flsbuf (int c, unix_FILE *file)
  98 {
  99   /* Compensate for putc's decrement.  */
 100   switch (++file->glue.magic)
 101     {
 102     case _GLUEMAGIC:
 103       return putc (c, *file->glue.streamp);
 104
 105     case  _IOMAGIC:
 106       return putc (c, (FILE *) file);
 107
 108     default:
 109       __set_errno (EINVAL);
 110       return EOF;
 111     }
 112 }