compiler/clib/ftruncate.c

   1 /*
   2     Copyright © 1995-2003, The AROS Development Team. All rights reserved.
   3     $Id$
   4
   5     POSIX function ftruncate().
   6 */
   7
   8 #include <dos/dos.h>
   9 #include <proto/dos.h>
  10 #include <fcntl.h>
  11 #include <errno.h>
  12 #include "__errno.h"
  13 #include "__open.h"
  14
  15 /*****************************************************************************
  16
  17     NAME */
  18 #include <unistd.h>
  19
  20         int ftruncate (
  21
  22 /*  SYNOPSIS */
  23         int   fd,
  24         off_t length)
  25
  26 /*  FUNCTION
  27         Truncate a file to a specified length
  28
  29     INPUTS
  30         fd     - the descriptor of the file being truncated.
  31                  The file must be open for writing
  32         lenght - The file will have at most this size
  33
  34     RESULT
  35         0 on success or -1 on errorr.
  36
  37     NOTES
  38         If the file previously was larger than this size, the extra  data
  39         is  lost.   If  the  file  previously  was  shorter, it is
  40         unspecified whether the  file  is  left  unchanged  or  is
  41         extended.  In  the  latter case the extended part reads as
  42         zero bytes.
  43
  44
  45     EXAMPLE
  46
  47     BUGS
  48
  49     SEE ALSO
  50         open(), truncate()
  51
  52     INTERNALS
  53
  54 ******************************************************************************/
  55 {
  56     ULONG oldpos;
  57     size_t size;
  58
  59     fdesc *fdesc = __getfdesc(fd);
  60
  61     if (!fdesc)
  62     {
  63         errno = EBADF;
  64         return -1;
  65     }
  66
  67     if (!(fdesc->flags & (O_WRONLY|O_RDWR)))
  68     {
  69         errno = EINVAL;
  70         return -1;
  71     }
  72
  73     oldpos = Seek(fdesc->fh, 0, OFFSET_END);
  74     size   = Seek(fdesc->fh, 0, OFFSET_CURRENT);
  75     Seek(fdesc->fh, oldpos, OFFSET_BEGINNING);
  76
  77     if ((length = SetFileSize(fdesc->fh, length, OFFSET_BEGINNING)) == -1)
  78     {
  79         errno = IoErr2errno(IoErr());
  80         return -1;
  81     }
  82     else
  83     if (size < length)
  84     {
  85         char buf[16]={0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0};
  86
  87         length -= size;
  88
  89         oldpos = Seek(fdesc->fh, size, OFFSET_BEGINNING);
  90
  91         while (length >= 16)
  92         {
  93             FWrite(fdesc->fh, buf, 16, 1);
  94             length -= 16;
  95         }
  96         if (length)
  97             FWrite(fdesc->fh, buf, length, 1);
  98
  99         Flush(fdesc->fh);
 100         Seek(fdesc->fh, oldpos, OFFSET_BEGINNING);
 101     }
 102
 103     return 0;
 104 }