compiler/clib/fseek.c

   1 /*
   2     Copyright © 1995-2008, 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 "__errno.h"
  13 #include "__stdio.h"
  14 #include "__fdesc.h"
  15
  16 /*****************************************************************************
  17
  18     NAME */
  19 #include <stdio.h>
  20
  21         int fseek (
  22
  23 /*  SYNOPSIS */
  24         FILE * stream,
  25         long   offset,
  26         int    whence)
  27
  28 /*  FUNCTION
  29         Change the current position in a stream.
  30
  31     INPUTS
  32         stream - Modify this stream
  33         offset, whence - How to modify the current position. whence
  34                 can be SEEK_SET, then offset is the absolute position
  35                 in the file (0 is the first byte), SEEK_CUR then the
  36                 position will change by offset (ie. -5 means to move
  37                 5 bytes to the beginning of the file) or SEEK_END.
  38                 SEEK_END means that the offset is relative to the
  39                 end of the file (-1 is the last byte and 0 is
  40                 the EOF).
  41
  42     RESULT
  43         0 on success and -1 on error. If an error occurred, the global
  44         variable errno is set.
  45
  46     NOTES
  47
  48     EXAMPLE
  49
  50     BUGS
  51     Not fully compatible with iso fseek, especially in 'ab' and 'a+b'
  52     modes
  53
  54     SEE ALSO
  55         fopen(), fwrite()
  56
  57     INTERNALS
  58
  59 ******************************************************************************/
  60 {
  61     int cnt = 0;
  62     int finalseekposition = 0;
  63     int eofposition = 0;
  64     struct FileInfoBlock *fib = NULL;
  65     BPTR fh = BNULL;
  66     fdesc *fdesc = __getfdesc(stream->fd);
  67
  68     if (!fdesc)
  69     {
  70             errno = EBADF;
  71             return -1;
  72     }
  73
  74     fh = (BPTR)(fdesc->fcb->fh);
  75
  76     /* This is buffered IO, flush the buffer before any Seek */
  77     Flush (fh);
  78
  79     /* Handling for fseek specific behaviour (not all cases handled) */
  80     /* Get current position */
  81     cnt = Seek (fh, 0, OFFSET_CURRENT);
  82     if (cnt == -1)
  83     {
  84         errno = IoErr2errno (IoErr ());
  85         return -1;
  86     }
  87
  88     /* Get file size */
  89     fib = AllocDosObject(DOS_FIB, NULL);
  90     if (!fib)
  91     {
  92         errno = IoErr2errno(IoErr());
  93         return -1;
  94     }
  95
  96     if (ExamineFH(fh, fib))
  97         eofposition = fib->fib_Size;
  98     else
  99     {
 100         /* Does not happen on sfs/affs */
 101         FreeDosObject(DOS_FIB, fib);
 102         fib = NULL;
 103         errno = EBADF;
 104         return -1;
 105     }
 106
 107     FreeDosObject(DOS_FIB, fib);
 108     fib = NULL;
 109
 110     switch(whence)
 111     {
 112         case SEEK_SET: finalseekposition = offset; break;
 113         case SEEK_CUR: finalseekposition = cnt + offset; break;
 114         case SEEK_END: finalseekposition = eofposition + offset; break;
 115         default:
 116             errno = EINVAL;
 117             return -1;
 118     }
 119
 120     /* Check conditions */
 121     /* Seek before beginning of file */
 122     if (finalseekposition < 0)
 123     {
 124         errno = EINVAL;
 125         return -1;
 126     }
 127
 128     /* Seek beyond end of file and in write mode */
 129     if (finalseekposition > eofposition)
 130     {
 131         if (fdesc->fcb->flags & O_WRITE)
 132         {
 133             /* Write '0' to fill up to requested size - compatible fseek does not write but allows write */
 134             int i = 0;
 135             int bytestowrite = finalseekposition - eofposition;
 136             int chunkcount = (bytestowrite)/128;
 137             char zeroarray[128] = {0};
 138
 139             Seek (fh, 0, OFFSET_END);
 140             for (i = 0; i < chunkcount; i++)
 141                 FWrite(fh, (STRPTR)zeroarray, 128, 1);
 142             FWrite(fh, (STRPTR)zeroarray, bytestowrite - (chunkcount * 128), 1);
 143             Flush (fh);
 144         }
 145     }
 146
 147     cnt = Seek (fh, finalseekposition, OFFSET_BEGINNING);
 148
 149     if (cnt == -1)
 150         errno = IoErr2errno (IoErr ());
 151     else
 152     {
 153         /* It's specified that upon success fseek should clear EOF flag
 154            so here we go.
 155         */
 156         stream->flags &= ~(_STDIO_EOF);
 157         cnt = 0;
 158     }
 159
 160     return cnt;
 161 } /* fseek */