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pread, pwrite - read from or write to a file descriptor at a given
#define _XOPEN_SOURCE 500
ssize_t pread(int fd, void *buf, size_t count, off_t offset);
ssize_t pwrite(int fd, const void *buf, size_t count, off_t offset);
pread() reads up to count bytes from file descriptor fd at offset
offset (from the start of the file) into the buffer starting at buf.
The file offset is not changed.
pwrite() writes up to count bytes from the buffer starting at buf to
the file descriptor fd at offset offset. The file offset is not
The file referenced by fd must be capable of seeking.
On success, the number of bytes read or written is returned (zero
indicates that nothing was written, in the case of pwrite(), or end of
file, in the case of pread), or -1 on error, in which case errno is set
to indicate the error.
pread() can fail and set errno to any error specified for read(2) or
lseek(2). pwrite() can fail and set errno to any error specified for
write(2) or lseek(2).
The pread() and pwrite() system calls were added to Linux in version
2.1.60; the entries in the i386 system call table were added in 2.1.69.
The libc support (including emulation on older kernels without the
system calls) was added in glibc 2.1.
lseek(2), read(2), write(2)