Write into a file without changing the file pointer
Synopsis:
#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 );
Arguments:
- 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 that you want to write. This amount must not exceed
SSIZE_MAX - sizeof(io_write_t) - sizeof(struct _xtype_offset)
(see <limits.h>), or the function fails and sets
errno to EOVERFLOW.
- offset
- The desired position inside the file.
Library:
libc
Use the -l c option to
qcc
to link against this library.
This library is usually included automatically.
Description:
The pwrite() and pwrite64() functions perform the same action as
write(),
except that they write into a given position without changing
the file pointer.
The pwrite64() function is a large-file support version of pwrite().
Note:
In QNX Neutrino 6.6 or later, the large-file support functions and data types
appear in the name space only if you define
_LARGEFILE64_SOURCE when you compile your code.
For more information, see
Classification
in What's in a Function Description?
Returns:
The number of bytes actually written, or -1 if an error occurred
(errno is set).
Errors:
- 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, filedes, 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
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
filedes.
- 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 device 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.
- EOVERFLOW
- An attempt was made to write an amount of data that when added to the sizes of the write message and extra type offset
structures exceeds the allowable limit.
- 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 filedes.
- ESPIPE
- The filedes argument is associated with a pipe, FIFO, or socket. The file
pointer remains unchanged.
Classification:
pwrite() is
POSIX 1003.1;
pwrite64() is
Large-file support
Safety: |
|
Cancellation point |
Yes |
Interrupt handler |
No |
Signal handler |
Yes |
Thread |
Yes |