Man Pages

ftruncate(3p) - phpMan ftruncate(3p) - phpMan

Command: man perldoc info search(apropos)  


FTRUNCATE(3P)              POSIX Programmer's Manual             FTRUNCATE(3P)



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may dif-
       fer (consult the corresponding Linux manual page for details of Linux behavior), or the interface  may  not  be
       implemented on Linux.

NAME
       ftruncate - truncate a file to a specified length

SYNOPSIS
       #include <unistd.h>

       int ftruncate(int fildes, off_t length);


DESCRIPTION
       If fildes is not a valid file descriptor open for writing, the ftruncate() function shall fail.

       If  fildes  refers to a regular file, the ftruncate() function shall cause the size of the file to be truncated
       to length. If the size of the file previously exceeded length, the extra data shall no longer be  available  to
       reads  on  the  file.  If the file previously was smaller than this size, ftruncate() shall either increase the
       size of the file or fail.   XSI-conformant systems shall increase the size of the file.  If the  file  size  is
       increased, the extended area shall appear as if it were zero-filled. The value of the seek pointer shall not be
       modified by a call to ftruncate().

       Upon successful completion, if fildes refers to a regular file, the ftruncate() function shall mark for  update
       the  st_ctime and st_mtime fields of the file and the S_ISUID and S_ISGID bits of the file mode may be cleared.
       If the ftruncate() function is unsuccessful, the file is unaffected.

       If the request would cause the file size to exceed the soft file size limit for the process, the request  shall
       fail and the implementation shall generate the SIGXFSZ signal for the thread.

       If fildes refers to a directory, ftruncate() shall fail.

       If fildes refers to any other file type, except a shared memory object, the result is unspecified.

       If  fildes  refers  to  a  shared  memory object, ftruncate() shall set the size of the shared memory object to
       length.

       If the effect of ftruncate() is to decrease the size of a shared memory object or memory mapped file and  whole
       pages beyond the new end were previously mapped, then the whole pages beyond the new end shall be discarded.

       If the Memory Protection option is supported, references to discarded pages shall result in the generation of a
       SIGBUS signal; otherwise, the result of such references is undefined.

       If the effect of ftruncate() is to increase the size of a shared memory object, it is unspecified  whether  the
       contents of any mapped pages between the old end-of-file and the new are flushed to the underlying object.

RETURN VALUE
       Upon  successful completion, ftruncate() shall return 0; otherwise, -1 shall be returned and errno set to indi-
       cate the error.

ERRORS
       The ftruncate() function shall fail if:

       EINTR  A signal was caught during execution.

       EINVAL The length argument was less than 0.

       EFBIG or EINVAL

              The length argument was greater than the maximum file size.

       EFBIG  The file is a regular file and length is greater than the offset maximum established in  the  open  file
              description associated with fildes.

       EIO    An I/O error occurred while reading from or writing to a file system.

       EBADF or EINVAL

              The fildes argument is not a file descriptor open for writing.

       EINVAL The fildes argument references a file that was opened without write permission.

       EROFS  The named file resides on a read-only file system.


       The following sections are informative.

EXAMPLES
       None.

APPLICATION USAGE
       None.

RATIONALE
       The  ftruncate()  function  is part of IEEE Std 1003.1-2001 as it was deemed to be more useful than truncate().
       The truncate() function is provided as an XSI extension.

FUTURE DIRECTIONS
       None.

SEE ALSO
       open(), truncate(), the Base Definitions volume of IEEE Std 1003.1-2001, <unistd.h>

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Stan-
       dard  for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifica-
       tions Issue 6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers,  Inc  and  The
       Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Stan-
       dard, the original IEEE and The Open Group Standard is the referee  document.  The  original  Standard  can  be
       obtained online at http://www.opengroup.org/unix/online.html .



IEEE/The Open Group                  2003                        FTRUNCATE(3P)