mirror of https://github.com/mkerrisk/man-pages
105 lines
2.7 KiB
Groff
105 lines
2.7 KiB
Groff
.\" Copyright (C) 1999 Joseph Samuel Myers.
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.\"
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one.
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.\"
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein. The author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" professionally.
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.\"
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\"
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.TH PREAD 2 2008-12-03 "Linux" "Linux Programmer's Manual"
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.SH NAME
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pread, pwrite \- read from or write to a file descriptor at a given offset
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.SH SYNOPSIS
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.B #define _XOPEN_SOURCE 500
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.sp
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.B #include <unistd.h>
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.sp
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.BI "ssize_t pread(int " fd ", void *" buf ", size_t " count \
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", off_t " offset );
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.sp
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.BI "ssize_t pwrite(int " fd ", const void *" buf ", size_t " count \
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", off_t " offset );
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.SH DESCRIPTION
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.BR pread ()
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reads up to
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.I count
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bytes from file descriptor
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.I fd
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at offset
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.I offset
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(from the start of the file) into the buffer starting at
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.IR buf .
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The file offset is not changed.
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.PP
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.BR pwrite ()
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writes up to
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.I count
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bytes from the buffer starting at
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.I buf
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to the file descriptor
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.I fd
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at offset
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.IR offset .
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The file offset is not changed.
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.PP
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The file referenced by
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.I fd
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must be capable of seeking.
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.SH "RETURN VALUE"
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On success, the number of bytes read or written is returned (zero
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indicates that nothing was written, in the case of
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.BR pwrite (),
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or
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end of file, in the case of
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.BR pread (),
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or \-1 on error, in which case
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.I errno
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is set to indicate the error.
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.SH ERRORS
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.BR pread ()
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can fail and set
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.I errno
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to any error specified for
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.BR read (2)
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or
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.BR lseek (2).
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.BR pwrite ()
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can fail and set
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.I errno
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to any error specified for
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.BR write (2)
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or
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.BR lseek (2).
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.SH VERSIONS
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The
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.BR pread ()
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and
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.BR pwrite ()
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system calls were added to Linux in
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version 2.1.60; the entries in the i386 system call table were added
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in 2.1.69.
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C library support (including emulation using
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.BR lseek (2)
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on older kernels without the system calls) was added in glibc 2.1.
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.SH "CONFORMING TO"
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POSIX.1-2001.
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.SH "SEE ALSO"
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.BR lseek (2),
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.BR read (2),
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.BR write (2),
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.BR feature_test_macros (7)
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