Write into a file without changing the file pointer
#include <unistd.h>
ssize_t pwrite( int filedes,
const void* buff,
size_t nbytes,
off_t offset );
ssize_t pwrite64( int filedes,
const void* buff,
size_t nbytes,
off64_t offset );
- filedes
- The file descriptor for the file you want to write in.
- buff
- A pointer to a buffer that contains the data you want to write.
- nbytes
- The number of bytes to write.
- offset
- The desired position inside the file.
libc
Use the -l c option to
qcc
to link against this library.
This library is usually included automatically.
The pwrite() function performs the same action as
write(),
except that it writes into a given position without changing
the file pointer.
The pwrite64() function is a 64-bit version of pwrite().
The number of bytes actually written, or -1 if an error occurred
(errno is set).
- EAGAIN
- The O_NONBLOCK flag is set for the file descriptor, and
the process would be delayed in the write operation.
- EBADF
- The file descriptor, fildes, isn't a valid file descriptor
open for writing.
- EFBIG
- One of the following occurred:
- An attempt was made to write a file that exceeds the maximum file size
or the process's file size limit, and there was no room for any bytes
to be written.
- The file is a regular file, nbytes is greater than 0,
and the starting position is greater than or equal to the offset
maximum established in the open file description associated with
fildes.
- EINTR
- The write operation was interrupted by a signal, and either no data
was transferred, or the resource manager responsible for that file
doesn't report partial transfers.
- EINVAL
- The offset argument is invalid; the value is negative.
The file pointer remains unchanged.
- EIO
- One of the following occurred:
- The process is a member of a background process group attempting to
write to its controlling terminal, TOSTOP is set,
the process is neither ignoring nor blocking SIGTTOU,
and the process group of the process is orphaned.
- A physical I/O error occurred (for example, a bad block on a disk). The
precise meaning is device-dependent.
- ENOBUFS
- Insufficient resources were available in the system to perform the
operation.
- ENOSPC
- There's no free space remaining on the device containing the file.
- ENOSYS
- The pwrite() function isn't implemented for the filesystem specified
by filedes.
- ENXIO
- One of the following occurred:
- A request was made of a nonexistent device, or the request was outside
the capabilities of the device.
- A hangup occurred on the STREAM being written to.
- EPIPE
- An attempt was made to write to a pipe (or FIFO) that isn't open for
reading by any process. A SIGPIPE signal is also sent to
the process.
- ERANGE
- The transfer request size was outside the range supported by the
STREAMS file associated with fildes.
- ESPIPE
- The fildes is associated with a pipe or FIFO.
The file pointer remains unchanged.
pwrite() is
POSIX 1003.1 XSI;
pwrite64() is
Large-file support
Safety: | |
Cancellation point |
Yes |
Interrupt handler |
No |
Signal handler |
Yes |
Thread |
Yes |
close(),
creat(),
dup(),
dup2(),
errno,
fcntl(),
lseek(),
open(),
pipe(),
pread(),
read(),
readv(),
select(),
write(),
writev()