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pwrite (2)
  • pwrite (2) ( Solaris man: Системные вызовы )
  • >> pwrite (2) ( FreeBSD man: Системные вызовы )
  • pwrite (2) ( Русские man: Системные вызовы )
  • pwrite (2) ( Linux man: Системные вызовы )
  • pwrite (3) ( POSIX man: Библиотечные вызовы )

  • BSD mandoc


     - write output


    Lb libc


       #include <sys/types.h>
       #include <sys/uio.h>
       #include <unistd.h>
    ssize_t write (int d const void *buf size_t nbytes);
    ssize_t pwrite (int d const void *buf size_t nbytes off_t offset);
    ssize_t writev (int d const struct iovec *iov int iovcnt);
    ssize_t pwritev (int d const struct iovec *iov int iovcnt off_t offset);


    The write ();
    system call attempts to write Fa nbytes of data to the object referenced by the descriptor Fa d from the buffer pointed to by Fa buf . The writev ();
    system call performs the same action, but gathers the output data from the Fa iovcnt buffers specified by the members of the Fa iov array: iov[0], iov[1], ..., iov[iovcnt-1]. The pwrite ();
    and pwritev ();
    system calls perform the same functions, but write to the specified position in the file without modifying the file pointer.

    For writev ();
    and pwritev (,);
    the Fa iovec structure is defined as:

    struct iovec {
            void   *iov_base;  /* Base address. */
            size_t iov_len;    /* Length. */

    Each Fa iovec entry specifies the base address and length of an area in memory from which data should be written. The writev ();
    system call will always write a complete area before proceeding to the next.

    On objects capable of seeking, the write ();
    starts at a position given by the pointer associated with Fa d , see lseek(2). Upon return from write (,);
    the pointer is incremented by the number of bytes which were written.

    Objects that are not capable of seeking always write from the current position. The value of the pointer associated with such an object is undefined.

    If the real user is not the super-user, then write ();
    clears the set-user-id bit on a file. This prevents penetration of system security by a user who ``captures'' a writable set-user-id file owned by the super-user.

    When using non-blocking I/O on objects such as sockets that are subject to flow control, write ();
    and writev ();
    may write fewer bytes than requested; the return value must be noted, and the remainder of the operation should be retried when possible.  


    Upon successful completion the number of bytes which were written is returned. Otherwise a -1 is returned and the global variable errno is set to indicate the error.  


    The write (,);
    writev (,);
    pwrite ();
    and pwritev ();
    system calls will fail and the file pointer will remain unchanged if:

    Bq Er EBADF
    The Fa d argument is not a valid descriptor open for writing.
    Bq Er EPIPE
    An attempt is made to write to a pipe that is not open for reading by any process.
    Bq Er EPIPE
    An attempt is made to write to a socket of type SOCK_STREAM that is not connected to a peer socket.
    Bq Er EFBIG
    An attempt was made to write a file that exceeds the process's file size limit or the maximum file size.
    Bq Er EFAULT
    Part of Fa iov or data to be written to the file points outside the process's allocated address space.
    Bq Er EINVAL
    The pointer associated with Fa d was negative.
    Bq Er ENOSPC
    There is no free space remaining on the file system containing the file.
    Bq Er EDQUOT
    The user's quota of disk blocks on the file system containing the file has been exhausted.
    Bq Er EIO
    An I/O error occurred while reading from or writing to the file system.
    Bq Er EINTR
    A signal interrupted the write before it could be completed.
    Bq Er EAGAIN
    The file was marked for non-blocking I/O, and no data could be written immediately.
    Bq Er EROFS
    An attempt was made to write over a disk label area at the beginning of a slice. Use disklabel(8) -W to enable writing on the disk label area.
    Bq Er EINVAL
    The value Fa nbytes is greater than INT_MAX

    In addition, writev ();
    and pwritev ();
    may return one of the following errors:

    The destination is no longer available when writing to a UNIX domain datagram socket on which connect(2) had been used to set a destination address.
    Bq Er EINVAL
    The Fa iovcnt argument was less than or equal to 0, or greater than IOV_MAX
    Bq Er EINVAL
    One of the Fa iov_len values in the Fa iov array was negative.
    Bq Er EINVAL
    The sum of the Fa iov_len values in the Fa iov array overflowed a 32-bit integer.
    The mbuf pool has been completely exhausted when writing to a socket.

    The pwrite ();
    and pwritev ();
    system calls may also return the following errors:

    Bq Er EINVAL
    The Fa offset value was negative.
    Bq Er ESPIPE
    The file descriptor is associated with a pipe, socket, or FIFO.



    fcntl(2), lseek(2), open(2), pipe(2), select(2)  


    The write ();
    system call is expected to conform to St -p1003.1-90 . The writev ();
    and pwrite ();
    system calls are expected to conform to St -xpg4.2 .  


    The pwritev ();
    system call appeared in Fx 6.0 . The pwrite ();
    function appeared in AT&T System V.4 . The writev ();
    system call appeared in BSD 4.2 The write ();
    function appeared in AT&T System v6 .




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