rom/dos/ungetc.c

   1 /*
   2     Copyright © 1995-2007, The AROS Development Team. All rights reserved.
   3     $Id$
   4
   5     Desc:
   6     Lang: english
   7 */
   8 #include <aros/debug.h>
   9
  10 #include <proto/exec.h>
  11 #include "dos_intern.h"
  12
  13 #ifndef EOF
  14 #define EOF -1
  15 #endif
  16
  17 /*****************************************************************************
  18
  19     NAME */
  20 #include <proto/dos.h>
  21
  22         AROS_LH2(LONG, UnGetC,
  23
  24 /*  SYNOPSIS */
  25         AROS_LHA(BPTR, file,      D1),
  26         AROS_LHA(LONG, character, D2),
  27
  28 /*  LOCATION */
  29
  30         struct DosLibrary *, DOSBase, 53, Dos)
  31
  32 /*  FUNCTION
  33         Push a character back into a read filehandle. If you've read
  34         a character from that file you may always push at least 1 character
  35         back. UnGetC(file,-1) ungets the last character read. This also
  36         works for EOF.
  37
  38     INPUTS
  39         file      - Filehandle you've read from.
  40         character - Character to push back or EOF.
  41
  42     RESULT
  43         !=0 if all went well, 0 if the character couldn't be pushed back.
  44         IoErr() gives additional information in that case.
  45
  46     NOTES
  47
  48     EXAMPLE
  49
  50     BUGS
  51
  52     SEE ALSO
  53         FGetC(), IoErr()
  54
  55     INTERNALS
  56
  57 *****************************************************************************/
  58 {
  59     AROS_LIBFUNC_INIT
  60
  61     struct Process *me = (struct Process *)FindTask(NULL);
  62     SIPTR *result;
  63
  64     ASSERT_VALID_PROCESS(me);
  65
  66     result=&me->pr_Result2;
  67
  68     /* Get pointer to filehandle */
  69     struct FileHandle *fh=(struct FileHandle *)BADDR(file);
  70
  71     /* If the file is in write mode there was nothing read recently */
  72     if(fh->fh_Flags&FHF_WRITE)
  73     {
  74         *result=ERROR_SEEK_ERROR;
  75         return 0;
  76     }
  77
  78     /* Unget EOF character if the last character read was an EOF */
  79     if(character==EOF&&fh->fh_End==0)
  80     {
  81         fh->fh_Pos++;
  82         return EOF;
  83     }
  84
  85     /* Test if I may unget a character on this file */
  86     if(fh->fh_Pos==0)
  87     {
  88         *result=ERROR_SEEK_ERROR;
  89         return 0;
  90     }
  91
  92     /* OK. Unget character and return. */
  93     fh->fh_Pos--;
  94     if(character!=EOF)
  95         ((UBYTE *)BADDR(fh->fh_Buf))[fh->fh_Pos]=character;
  96     return character?character:1;
  97     AROS_LIBFUNC_EXIT
  98 } /* UnGetC */