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