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FTRUNCATE
Section: POSIX Programmer's Manual (3P)
Updated: 2003
Index
Return to Main Contents
PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (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 indicate
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, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications 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 Standard, 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 .
Index
- PROLOG
-
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- EXAMPLES
-
- APPLICATION USAGE
-
- RATIONALE
-
- FUTURE DIRECTIONS
-
- SEE ALSO
-
- COPYRIGHT
-
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