compiler/clib/fseek.c

   1 /*
   2     Copyright © 1995-2012, The AROS Development Team. All rights reserved.
   3     $Id$
   4
   5     Change the position in a stream.
   6 */
   7
   8 #include <fcntl.h>
   9 #include <errno.h>
  10 #include <dos/dos.h>
  11 #include <proto/dos.h>
  12 #include "__stdio.h"
  13 #include "__fdesc.h"
  14
  15 /*****************************************************************************
  16
  17     NAME */
  18 #include <stdio.h>
  19
  20         int fseek (
  21
  22 /*  SYNOPSIS */
  23         FILE * stream,
  24         long   offset,
  25         int    whence)
  26
  27 /*  FUNCTION
  28         Change the current position in a stream.
  29
  30     INPUTS
  31         stream - Modify this stream
  32         offset, whence - How to modify the current position. whence
  33                 can be SEEK_SET, then offset is the absolute position
  34                 in the file (0 is the first byte), SEEK_CUR then the
  35                 position will change by offset (ie. -5 means to move
  36                 5 bytes to the beginning of the file) or SEEK_END.
  37                 SEEK_END means that the offset is relative to the
  38                 end of the file (-1 is the last byte and 0 is
  39                 the EOF).
  40
  41     RESULT
  42         0 on success and -1 on error. If an error occurred, the global
  43         variable errno is set.
  44
  45     NOTES
  46
  47     EXAMPLE
  48
  49     BUGS
  50     Not fully compatible with iso fseek, especially in 'ab' and 'a+b'
  51     modes
  52
  53     SEE ALSO
  54         fopen(), fwrite()
  55
  56     INTERNALS
  57
  58 ******************************************************************************/
  59 {
  60     int cnt = 0;
  61     int finalseekposition = 0;
  62     int eofposition = 0;
  63     struct FileInfoBlock *fib = NULL;
  64     BPTR fh = BNULL;
  65     fdesc *fdesc = __getfdesc(stream->fd);
  66
  67     if (!fdesc)
  68     {
  69             errno = EBADF;
  70             return -1;
  71     }
  72
  73     fh = (BPTR)(fdesc->fcb->fh);
  74
  75     /* This is buffered IO, flush the buffer before any Seek */
  76     Flush (fh);
  77
  78     /* Handling for fseek specific behaviour (not all cases handled) */
  79     /* Get current position */
  80     cnt = Seek (fh, 0, OFFSET_CURRENT);
  81     if (cnt == -1)
  82     {
  83         errno = __arosc_ioerr2errno (IoErr ());
  84         return -1;
  85     }
  86
  87     /* Get file size */
  88     fib = AllocDosObject(DOS_FIB, NULL);
  89     if (!fib)
  90     {
  91         errno = __arosc_ioerr2errno(IoErr());
  92         return -1;
  93     }
  94
  95     if (ExamineFH(fh, fib))
  96         eofposition = fib->fib_Size;
  97     else
  98     {
  99         /* Does not happen on sfs/affs */
 100         FreeDosObject(DOS_FIB, fib);
 101         fib = NULL;
 102         errno = EBADF;
 103         return -1;
 104     }
 105
 106     FreeDosObject(DOS_FIB, fib);
 107     fib = NULL;
 108
 109     switch(whence)
 110     {
 111         case SEEK_SET: finalseekposition = offset; break;
 112         case SEEK_CUR: finalseekposition = cnt + offset; break;
 113         case SEEK_END: finalseekposition = eofposition + offset; break;
 114         default:
 115             errno = EINVAL;
 116             return -1;
 117     }
 118
 119     /* Check conditions */
 120     /* Seek before beginning of file */
 121     if (finalseekposition < 0)
 122     {
 123         errno = EINVAL;
 124         return -1;
 125     }
 126
 127     /* Seek beyond end of file and in write mode */
 128     if (finalseekposition > eofposition)
 129     {
 130         if (fdesc->fcb->flags & O_WRITE)
 131         {
 132             /* Write '0' to fill up to requested size - compatible fseek does not write but allows write */
 133             int i = 0;
 134             int bytestowrite = finalseekposition - eofposition;
 135             int chunkcount = (bytestowrite)/128;
 136             char zeroarray[128] = {0};
 137
 138             Seek (fh, 0, OFFSET_END);
 139             for (i = 0; i < chunkcount; i++)
 140                 FWrite(fh, (STRPTR)zeroarray, 128, 1);
 141             FWrite(fh, (STRPTR)zeroarray, bytestowrite - (chunkcount * 128), 1);
 142             Flush (fh);
 143         }
 144     }
 145
 146     cnt = Seek (fh, finalseekposition, OFFSET_BEGINNING);
 147
 148     if (cnt == -1)
 149         errno = __arosc_ioerr2errno (IoErr ());
 150     else
 151     {
 152         /* It's specified that upon success fseek should clear EOF flag
 153            so here we go.
 154         */
 155         stream->flags &= ~(_STDIO_EOF);
 156         cnt = 0;
 157     }
 158
 159     return cnt;
 160 } /* fseek */