2004-11-03 13:51:07 +00:00
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.\" 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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2007-04-12 22:42:49 +00:00
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.\"
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2004-11-03 13:51:07 +00:00
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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.\" manual page may be incorrect or out-of-date.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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2007-04-12 22:42:49 +00:00
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.\"
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2004-11-03 13:51:07 +00:00
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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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2010-11-21 05:39:03 +00:00
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.TH PREAD 2 2010-11-21 "Linux" "Linux Programmer's Manual"
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2004-11-03 13:51:07 +00:00
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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 #include <unistd.h>
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.sp
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2008-07-06 14:54:26 +00:00
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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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2004-11-03 13:51:07 +00:00
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.sp
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2008-07-06 14:54:26 +00:00
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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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2010-09-18 03:35:39 +00:00
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.sp
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.in -4n
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Feature Test Macro Requirements for glibc (see
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.BR feature_test_macros (7)):
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.in
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.PD 0
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.ad l
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.sp
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.BR pread (),
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.BR pwrite ():
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.RS 4
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brk.2, chroot.2, faccessat.2, fchmodat.2, fchownat.2, fstatat.2, futimesat.2, getdtablesize.2, getpagesize.2, getsid.2, linkat.2, mkdirat.2, mknodat.2, openat.2, pread.2, readlinkat.2, renameat.2, setpgid.2, sigaltstack.2, symlinkat.2, sync.2, timer_create.2, timer_delete.2, timer_getoverrun.2, timer_settime.2, unlinkat.2, utimensat.2, vfork.2, acosh.3, asinh.3, atanh.3, dirfd.3, dprintf.3, ecvt.3, expm1.3, fexecve.3, fmemopen.3, gcvt.3, getcwd.3, gethostid.3, getpass.3, getsubopt.3, getw.3, mbsnrtowcs.3, mkfifoat.3, mkstemp.3, mktemp.3, opendir.3, posix_memalign.3, rint.3, siginterrupt.3, stpcpy.3, stpncpy.3, strdup.3, strerror.3, strnlen.3, strsignal.3, strtol.3, strtoul.3, ualarm.3, usleep.3, wcpcpy.3, wcpncpy.3, wcscasecmp.3, wcsdup.3, wcsncasecmp.3, wcsnlen.3, wcsnrtombs.3: ffix
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
2010-09-19 06:02:38 +00:00
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_XOPEN_SOURCE\ >=\ 500
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chdir.2, chmod.2, chown.2, gethostname.2, getsid.2, pread.2, setpgid.2, sigaltstack.2, stat.2, truncate.2, wait.2, dirfd.3, getsubopt.3, mkdtemp.3, mkstemp.3, siginterrupt.3, strdup.3: Simplify feature test macro requirements
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
2010-09-26 15:16:57 +00:00
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.br
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|| /* Since glibc 2.12: */ _POSIX_C_SOURCE\ >=\ 200809L
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2010-09-18 03:35:39 +00:00
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.RE
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.ad
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.PD
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2004-11-03 13:51:07 +00:00
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.SH DESCRIPTION
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2005-10-19 07:07:02 +00:00
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.BR pread ()
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2004-11-03 13:51:07 +00:00
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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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2005-10-19 07:07:02 +00:00
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.BR pwrite ()
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2004-11-03 13:51:07 +00:00
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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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2007-05-12 09:06:04 +00:00
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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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2007-05-12 13:19:09 +00:00
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end of file, in the case of
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2010-06-12 12:35:03 +00:00
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.BR pread ()),
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2007-05-12 13:19:09 +00:00
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or \-1 on error, in which case
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2004-11-03 13:51:07 +00:00
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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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2005-10-19 06:54:38 +00:00
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.BR pread ()
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2004-11-03 13:51:07 +00:00
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can fail and set
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.I errno
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2007-05-12 09:06:04 +00:00
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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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2005-10-19 06:54:38 +00:00
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.BR pwrite ()
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2004-11-03 13:51:07 +00:00
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can fail and set
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.I errno
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2007-05-12 09:06:04 +00:00
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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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2007-05-18 11:59:14 +00:00
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.SH VERSIONS
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2007-05-12 09:06:04 +00:00
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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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2004-11-03 13:51:07 +00:00
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version 2.1.60; the entries in the i386 system call table were added
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2007-04-24 16:44:51 +00:00
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in 2.1.69.
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2008-12-05 20:01:19 +00:00
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C library support (including emulation using
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2008-12-03 19:25:03 +00:00
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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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2007-05-18 16:06:42 +00:00
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.SH "CONFORMING TO"
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POSIX.1-2001.
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2010-11-21 05:39:03 +00:00
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.SH NOTES
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On Linux, the underlying system calls were renamed
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in kernel 2.6:
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.BR pread ()
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became
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.BR pread64 (),
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and
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.BR pwrite ()
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became
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2010-12-03 05:54:08 +00:00
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.BR pwrite64 ().
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2010-11-21 05:39:03 +00:00
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The system call numbers remained the same.
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The glibc
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.BR pread ()
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and
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.BR pwrite ()
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wrapper functions transparently deal with the change.
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2004-11-03 13:51:07 +00:00
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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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2010-11-16 05:50:28 +00:00
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.BR readv (2),
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getresuid.2, intro.2, mremap.2, open.2, poll.2, posix_fadvise.2, pread.2, remap_file_pages.2, setresuid.2, signal.2, splice.2, sync_file_range.2, tee.2, vmsplice.2, INFINITY.3, asprintf.3, assert_perror.3, basename.3, bsd_signal.3, canonicalize_file_name.3, clog10.3, crypt.3, dl_iterate_phdr.3, dlopen.3, dprintf.3, encrypt.3, exp10.3, fcloseall.3, fenv.3, ffs.3, fmemopen.3, fopencookie.3, ftw.3, getdate.3, getline.3, getloadavg.3, getopt.3, getsubopt.3, getutent.3, grantpt.3, hsearch.3, intro.3, lseek64.3, memmem.3, mempcpy.3, mq_receive.3, mq_send.3, posix_fallocate.3, pow10.3, program_invocation_name.3, ptsname.3, putgrent.3, readdir.3, sigset.3, sincos.3, stpcpy.3, stpncpy.3, strchr.3, strfry.3, strnlen.3, strptime.3, strsignal.3, strstr.3, strverscmp.3, swab.3, sysv_signal.3, tsearch.3, unlocked_stdio.3, unlockpt.3, wcpcpy.3, wcpncpy.3, wcsdup.3, wcwidth.3: SEE ALSO: Remove redundant reference to feature_test_macros(7)
Reported-by: Florian Lehmann <flo.lehmann@googlemail.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
2010-10-31 05:05:22 +00:00
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.BR write (2)
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