stdio/glue.c

   1 /* Copyright (C) 1991, 1992 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
  16 not, write to the Free Software Foundation, Inc., 675 Mass Ave,
  17 Cambridge, MA 02139, 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 <ansidecl.h>
  31 #include <stdio.h>
  32 #include <errno.h>
  33
  34 typedef union
  35   {
  36     struct
  37       {
  38         int magic;
  39         FILE **streamp;         /* Overlaps GNU stdio `bufp' member.  */
  40         /* These two overlap the GNU stdio `get_limit' and `put_limit'
  41            members.  They must be <= `streamp'/`bufp' for GNU getc and putc
  42            to do the right thing.  */
  43         FILE **streamp2, **streamp3;
  44       } glue;
  45     struct _iobuf
  46       {
  47         int _cnt;
  48         unsigned char *_ptr;
  49         unsigned char *_base;
  50         int _bufsiz;
  51         short int _flag;
  52         char _file;
  53       } unix_iobuf;
  54     FILE gnu_stream;
  55   } unix_FILE;
  56
  57 /* These are the Unix stdio's stdin, stdout, and stderr.
  58    In Unix stdin is (&_iob[0]), stdout is (&_iob[1]), and stderr is
  59    (&_iob[2]).  The magic number marks these as glued streams.  The
  60    __validfp macro in stdio.h is used by every stdio function.  It checks
  61    for glued streams, and replaces them with the GNU stdio stream.  */
  62 unix_FILE _iob[] =
  63   {
  64 #define S(name) { { _GLUEMAGIC, &name, &name, &name } }
  65     S (stdin),
  66     S (stdout),
  67     S (stderr),
  68 #undef  S
  69   };
  70
  71 /* Called by the Unix stdio `getc' macro.
  72    The macro is assumed to look something like:
  73        (--file->_cnt < 0 ? _filbuf (file) ...)
  74    In a Unix stdio FILE `_cnt' is the first element.
  75    In a GNU stdio or glued FILE, the first element is the magic number.  */
  76 int
  77 DEFUN(_filbuf, (file), unix_FILE *file)
  78 {
  79   switch (++file->glue.magic)   /* Compensate for Unix getc's decrement.  */
  80     {
  81     case _GLUEMAGIC:
  82       /* This is a glued stream.  */
  83       return getc (*file->glue.streamp);
  84
  85     case  _IOMAGIC:
  86       /* This is a normal GNU stdio stream.  */
  87       return getc ((FILE *) file);
  88
  89     default:
  90       /* Bogus stream.  */
  91       errno = EINVAL;
  92       return EOF;
  93     }
  94 }
  95
  96 /* Called by the Unix stdio `putc' macro.  Much like getc, above.  */
  97 int
  98 DEFUN(_flsbuf, (c, file),
  99       int c AND unix_FILE *file)
 100 {
 101   /* Compensate for putc's decrement.  */
 102   switch (++file->glue.magic)
 103     {
 104     case _GLUEMAGIC:
 105       return putc (c, *file->glue.streamp);
 106
 107     case  _IOMAGIC:
 108       return putc (c, (FILE *) file);
 109
 110     default:
 111       errno = EINVAL;
 112       return EOF;
 113     }
 114 }