rom/dos/seek.c

   1 /*
   2     Copyright © 1995-2007, The AROS Development Team. All rights reserved.
   3     $Id$
   4
   5     Desc: Change the current read/write position in a file.
   6     Lang: english
   7 */
   8 #include <proto/exec.h>
   9 #include <dos/filesystem.h>
  10 #include "dos_intern.h"
  11
  12 /*****************************************************************************
  13
  14     NAME */
  15 #include <proto/dos.h>
  16
  17         AROS_LH3(LONG, Seek,
  18
  19 /*  SYNOPSIS */
  20         AROS_LHA(BPTR, file,     D1),
  21         AROS_LHA(LONG, position, D2),
  22         AROS_LHA(LONG, mode,     D3),
  23
  24 /*  LOCATION */
  25         struct DosLibrary *, DOSBase, 11, Dos)
  26
  27 /*  FUNCTION
  28         Changes the current read/write position in a file and/or
  29         reads the current position, e.g to get the current position
  30         do a Seek(file,0,OFFSET_CURRENT).
  31
  32         This function may fail (obviously) on certain devices such
  33         as pipes or console handlers.
  34
  35     INPUTS
  36         file     - filehandle
  37         position - relative offset in bytes (positive, negative or 0).
  38         mode     - Where to count from. Either OFFSET_BEGINNING,
  39                    OFFSET_CURRENT or OFFSET_END.
  40
  41     RESULT
  42         Absolute position in bytes before the Seek(), -1 if an error
  43         happened. IoErr() will give additional information in that case.
  44
  45     NOTES
  46
  47     EXAMPLE
  48
  49     BUGS
  50
  51     SEE ALSO
  52
  53     INTERNALS
  54
  55 *****************************************************************************/
  56 {
  57     AROS_LIBFUNC_INIT
  58
  59     /* Get pointer to filehandle. */
  60     struct FileHandle *fh = (struct FileHandle *)BADDR(file);
  61     LONG               offset = 0, ret;
  62
  63     /* If the file is in append mode, seeking is not allowed. */
  64     if( fh->fh_Flags & FHF_APPEND )
  65     {
  66         return InternalSeek( fh, 0, OFFSET_CURRENT, DOSBase );
  67     }
  68
  69     /* If the file is in write mode flush it. */
  70     if( fh->fh_Flags & FHF_WRITE )
  71     {
  72         InternalFlush( fh, DOSBase );
  73     }
  74     else
  75     {
  76         /* Read mode. Adjust the offset so that buffering is
  77            taken into account. */
  78         if (fh->fh_Pos < fh->fh_End && mode == OFFSET_CURRENT)
  79             offset = (LONG)(fh->fh_Pos - fh->fh_End);
  80
  81
  82         /* Read mode. Just reinit the buffers. We can't call
  83            Flush() in this case as that would end up in
  84            recursion. */
  85         fh->fh_Pos = fh->fh_End = fh->fh_Buf;
  86     }
  87
  88     ret = InternalSeek( fh, position + offset, mode, DOSBase );
  89     return (ret == -1) ? -1 : (ret + offset);
  90
  91     AROS_LIBFUNC_EXIT
  92 } /* Seek */