pread, pwrite — read from or write to a file descriptor at a given offset
#define _XOPEN_SOURCE 500 #include <unistd.h>
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 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), feature_test_macros(7)
|