1PREAD(2) Linux Programmer's Manual PREAD(2)
2
6 pread, pwrite - read from or write to a file descriptor at a given off‐
7 set
8
10 #define _XOPEN_SOURCE 500
11 #include <unistd.h>
13 ssize_t pread(int fd, void *buf, size_t count, off_t offset);
15 ssize_t pwrite(int fd, const void *buf, size_t count, off_t offset);
17
19 pread() reads up to count bytes from file descriptor fd at offset off‐
20 set (from the start of the file) into the buffer starting at buf. The
21 file offset is not changed.
22 pwrite() writes up to count bytes from the buffer starting at buf to
24 the file descriptor fd at offset offset. The file offset is not
25 changed.
26 The file referenced by fd must be capable of seeking.
28
30 On success, the number of bytes read or written is returned (zero indi‐
31 cates that nothing was written, in the case of pwrite(), or end of
32 file, in the case of pread(), or -1 on error, in which case errno is
33 set to indicate the error.
34
36 pread() can fail and set errno to any error specified for read(2) or
37 lseek(2). pwrite() can fail and set errno to any error specified for
38 write(2) or lseek(2).
39
41 The pread() and pwrite() system calls were added to Linux in version
42 2.1.60; the entries in the i386 system call table were added in 2.1.69.
43 C library support (including emulation using lseek(2) on older kernels
44 without the system calls) was added in glibc 2.1.
45
47 POSIX.1-2001.
48
50 lseek(2), read(2), write(2), feature_test_macros(7)
51
53 This page is part of release 3.22 of the Linux man-pages project. A
54 description of the project, and information about reporting bugs, can
55 be found at http://www.kernel.org/doc/man-pages/.
56Linux 2008-12-03 PREAD(2)