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_intern.h"
  10
  11 /*****************************************************************************
  12
  13     NAME */
  14 #include <proto/dos.h>
  15
  16         AROS_LH3(LONG, Seek,
  17
  18 /*  SYNOPSIS */
  19         AROS_LHA(BPTR, file,     D1),
  20         AROS_LHA(LONG, position, D2),
  21         AROS_LHA(LONG, mode,     D3),
  22
  23 /*  LOCATION */
  24         struct DosLibrary *, DOSBase, 11, Dos)
  25
  26 /*  FUNCTION
  27         Changes the current read/write position in a file and/or
  28         reads the current position, e.g to get the current position
  29         do a Seek(file,0,OFFSET_CURRENT).
  30
  31         This function may fail (obviously) on certain devices such
  32         as pipes or console handlers.
  33
  34     INPUTS
  35         file     - filehandle
  36         position - relative offset in bytes (positive, negative or 0).
  37         mode     - Where to count from. Either OFFSET_BEGINNING,
  38                    OFFSET_CURRENT or OFFSET_END.
  39
  40     RESULT
  41         Absolute position in bytes before the Seek(), -1 if an error
  42         happened. IoErr() will give additional information in that case.
  43
  44     NOTES
  45
  46     EXAMPLE
  47
  48     BUGS
  49
  50     SEE ALSO
  51
  52     INTERNALS
  53
  54 *****************************************************************************/
  55 {
  56     AROS_LIBFUNC_INIT
  57
  58     /* Get pointer to filehandle. */
  59     struct FileHandle *fh = (struct FileHandle *)BADDR(file);
  60     LONG               offset = 0, ret;
  61
  62     if (fh == NULL) {
  63         SetIoErr(ERROR_INVALID_LOCK);
  64         return -1;
  65     }
  66
  67     /* If the file is in append mode, seeking is not allowed. */
  68     if( fh->fh_Flags & FHF_APPEND )
  69     {
  70         return InternalSeek( fh, 0, OFFSET_CURRENT, DOSBase );
  71     }
  72
  73     /* If the file is in write mode flush it. */
  74     if( fh->fh_Flags & FHF_WRITE )
  75     {
  76         InternalFlush( fh, DOSBase );
  77     }
  78     else
  79     {
  80         /* Read mode. Adjust the offset so that buffering is
  81            taken into account. */
  82         if (fh->fh_Pos < fh->fh_End && mode == OFFSET_CURRENT)
  83             offset = (LONG)(fh->fh_Pos - fh->fh_End);
  84
  85
  86         /* Read mode. Just reinit the buffers. We can't call
  87            Flush() in this case as that would end up in
  88            recursion. */
  89         fh->fh_Pos = fh->fh_End = 0;
  90     }
  91
  92     ret = InternalSeek( fh, position + offset, mode, DOSBase );
  93     return (ret == -1) ? -1 : (ret + offset);
  94
  95     AROS_LIBFUNC_EXIT
  96 } /* Seek */