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pread() - Unix, Linux System Call
pread, pwrite - read from or write to a file descriptor at a given offset
#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 changed.
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
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.