1 .\" Copyright (C) 1999 Joseph Samuel Myers.
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25 .TH PREAD 2 2012-04-30 "Linux" "Linux Programmer's Manual"
27 pread, pwrite \- read from or write to a file descriptor at a given offset
29 .B #include <unistd.h>
31 .BI "ssize_t pread(int " fd ", void *" buf ", size_t " count \
34 .BI "ssize_t pwrite(int " fd ", const void *" buf ", size_t " count \
38 Feature Test Macro Requirements for glibc (see
39 .BR feature_test_macros (7)):
47 _XOPEN_SOURCE\ >=\ 500
49 || /* Since glibc 2.12: */ _POSIX_C_SOURCE\ >=\ 200809L
57 bytes from file descriptor
61 (from the start of the file) into the buffer starting at
63 The file offset is not changed.
68 bytes from the buffer starting at
70 to the file descriptor
74 The file offset is not changed.
76 The file referenced by
78 must be capable of seeking.
80 On success, the number of bytes read or written is returned (zero
81 indicates that nothing was written, in the case of
84 end of file, in the case of
86 or \-1 on error, in which case
88 is set to indicate the error.
93 to any error specified for
100 to any error specified for
109 system calls were added to Linux in
110 version 2.1.60; the entries in the i386 system call table were added
112 C library support (including emulation using
114 on older kernels without the system calls) was added in glibc 2.1.
118 On Linux, the underlying system calls were renamed
127 The system call numbers remained the same.
132 wrapper functions transparently deal with the change.
134 POSIX requires that opening a file with the
136 flag should have no affect on the location at which
139 However, on Linux, if a file is opened with
140 .\" FIXME https://bugzilla.kernel.org/show_bug.cgi?id=43178
143 appends data to the end of the file, regardless of the value of