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131 lines
4.5 KiB
Plaintext
131 lines
4.5 KiB
Plaintext
.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved
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.TH "FTRUNCATE" 3P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
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.\" ftruncate
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.SH NAME
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ftruncate \- truncate a file to a specified length
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.SH SYNOPSIS
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.LP
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\fB#include <unistd.h>
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.br
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.sp
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int ftruncate(int\fP \fIfildes\fP\fB, off_t\fP \fIlength\fP\fB);
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.br
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\fP
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.SH DESCRIPTION
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.LP
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If \fIfildes\fP is not a valid file descriptor open for writing, the
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\fIftruncate\fP() function shall fail.
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.LP
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If \fIfildes\fP refers to a regular file, the \fIftruncate\fP() function
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shall cause the size of the file to be truncated to
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\fIlength\fP. If the size of the file previously exceeded \fIlength\fP,
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the extra data shall no longer be available to reads on
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the file. If the file previously was smaller than this size, \fIftruncate\fP()
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shall either increase the size of the file or fail.
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\ XSI-conformant systems shall increase the size of the file.
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If the file size is increased, the extended area shall appear as if
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it were zero-filled. The value of the seek pointer shall not be
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modified by a call to \fIftruncate\fP().
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.LP
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Upon successful completion, if \fIfildes\fP refers to a regular file,
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the \fIftruncate\fP() function shall mark for update the
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\fIst_ctime\fP and \fIst_mtime\fP fields of the file and the S_ISUID
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and S_ISGID bits of the file mode may be cleared. If the
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\fIftruncate\fP() function is unsuccessful, the file is unaffected.
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.LP
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If the request would cause the file size to exceed the soft file size
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limit for the process, the request shall fail and the
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implementation shall generate the SIGXFSZ signal for the thread.
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.LP
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If \fIfildes\fP refers to a directory, \fIftruncate\fP() shall fail.
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.LP
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If \fIfildes\fP refers to any other file type, except a shared memory
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object, the result is unspecified.
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.LP
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If \fIfildes\fP refers to a shared memory object, \fIftruncate\fP()
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shall set the size of the shared memory object to
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\fIlength\fP.
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.LP
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If the effect of \fIftruncate\fP() is to decrease the size of a shared
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memory object or memory mapped file and whole pages beyond
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the new end were previously mapped, then the whole pages beyond the
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new end shall be discarded.
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.LP
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If the Memory Protection option is supported, references to discarded
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pages shall result in the generation of a SIGBUS signal;
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otherwise, the result of such references is undefined.
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.LP
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If the effect of \fIftruncate\fP() is to increase the size of a shared
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memory object, it is unspecified whether the contents of
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any mapped pages between the old end-of-file and the new are flushed
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to the underlying object.
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.SH RETURN VALUE
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.LP
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Upon successful completion, \fIftruncate\fP() shall return 0; otherwise,
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-1 shall be returned and \fIerrno\fP set to indicate
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the error.
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.SH ERRORS
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.LP
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The \fIftruncate\fP() function shall fail if:
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.TP 7
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.B EINTR
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A signal was caught during execution.
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.TP 7
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.B EINVAL
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The \fIlength\fP argument was less than 0.
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.TP 7
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.B EFBIG \fRor\fP EINVAL
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.sp
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The \fIlength\fP argument was greater than the maximum file size.
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.TP 7
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.B EFBIG
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The file is a regular file and \fIlength\fP is greater than the offset
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maximum established in the open file description associated
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with \fIfildes\fP.
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.TP 7
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.B EIO
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An I/O error occurred while reading from or writing to a file system.
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.TP 7
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.B EBADF \fRor\fP EINVAL
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.sp
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The \fIfildes\fP argument is not a file descriptor open for writing.
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.TP 7
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.B EINVAL
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The \fIfildes\fP argument references a file that was opened without
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write permission.
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.TP 7
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.B EROFS
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The named file resides on a read-only file system.
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.sp
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.LP
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\fIThe following sections are informative.\fP
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.SH EXAMPLES
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.LP
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None.
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.SH APPLICATION USAGE
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.LP
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None.
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.SH RATIONALE
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.LP
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The \fIftruncate\fP() function is part of IEEE\ Std\ 1003.1-2001 as
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it was deemed to be more useful than \fItruncate\fP(). The \fItruncate\fP()
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function is
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provided as an XSI extension.
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.SH FUTURE DIRECTIONS
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.LP
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None.
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.SH SEE ALSO
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.LP
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\fIopen\fP() , \fItruncate\fP() , the Base Definitions volume of
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IEEE\ Std\ 1003.1-2001, \fI<unistd.h>\fP
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.SH COPYRIGHT
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Portions of this text are reprinted and reproduced in electronic form
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from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
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-- Portable Operating System Interface (POSIX), The Open Group Base
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Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
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Electrical and Electronics Engineers, Inc and The Open Group. In the
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event of any discrepancy between this version and the original IEEE and
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The Open Group Standard, the original IEEE and The Open Group Standard
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is the referee document. The original Standard can be obtained online at
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http://www.opengroup.org/unix/online.html .
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