WRITE(2) BSD System Calls Manual WRITE(2)

NAME
     ppwwrriittee, wwrriittee, wwrriitteevv - write output

LLIIBBRRAARRYY
     Standard C Library (libc, -lc)

SYNOPSIS
     ##iinncclluuddee <>

     ssizet
     ppwwrriittee(int fildes, const void *buf, sizet nbyte, offt offset);

     ssizet
     wwrriittee(int fildes, const void *buf, sizet nbyte);

     ##iinncclluuddee <>

     ssizet
     wwrriitteevv(int fildes, const struct iovec *iov, int iovcnt);

DESCRIPTION
     WWrriittee() attempts to write nbyte of data to the object referenced by the
     descriptor fildes from the buffer pointed to by buf.  WWrriitteevv() performs
     the same action, but gathers the output data from the iovcnt buffers
     specified by the members of the iov array: iov[0], iov[1], ...,
     iov[iovcnt-1].  PPwwrriittee() performs the same function, but writes to the
     specified position in the file without modifying the file pointer.

     For wwrriitteevv(), the iovec structure is defined as:

           struct iovec {
                   char   *iovbase;  /* Base address. */
                   sizet iovlen;    /* Length. */
           };

     Each iovec entry specifies the base address and length of an area in mem-
     ory from which data should be written.  WWrriitteevv() will always write a com-
     plete area before proceeding to the next.

     On objects capable of seeking, the wwrriittee() starts at a position given by
     the pointer associated with fildes, see lseek(2).  Upon return from
     wwrriittee(), 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 wwrriittee() 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, wwrriittee() and wwrriitteevv() may write fewer bytes than
     requested; the return value must be noted, and the remainder of the oper-
     ation should be retried when possible.

RETURN VALUES
     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.

EERRRROORRSS
     The wwrriittee(), wwrriitteevv(), and ppwwrriittee() system calls will fail and the file
     pointer will remain unchanged if:

     [EDQUOT]           The user's quota of disk blocks on the file system
                        containing the file is exhausted.

     [EFAULT]           Part of iov or data to be written to the file points
                        outside the process's allocated address space.

     [EINVAL]           The pointer associated with fildes is negative.

     The wwrriittee() and ppwwrriittee() system calls will fail and the file pointer will
     remain unchanged if:

     [EAGAIN]           The file is marked for non-blocking I/O, and no data
                        could be written immediately.

     [EBADF]            fildes is not a valid file descriptor open for writ-
                        ing.

     [ECONNRESET]       A write is attempted on a socket that is not con-
                        nected.

     [EFBIG]            An attempt is made to write a file that exceeds the
                        process's file size limit or the maximum file size.

     [EFBIG]            The file is a regular file, nbyte 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]            A signal interrupts the write before it could be com-
                        pleted.

     [EIO]              An I/O error occurs while reading from or writing to
                        the file system.

     [ENETDOWN]         A write is attempted on a socket and the local network
                        interface used to reach the destination is down.

     [ENETUNREACH]      A write is attempted on a socket and no route to the
                        network is present.

     [ENOSPC]           There is no free space remaining on the file system
                        containing the file.

     [ENXIO]            A request is made of a nonexistent device, or the
                        request is outside the capabilities of the device.

     [EPIPE]            An attempt is made to write to a pipe that is not open
                        for reading by any process.

     [EPIPE]            An attempt is made to write to a socket of type
                        SOCKSTREAM that is not connected to a peer socket.

     The wwrriittee() and wwrriitteevv() calls may also return the following errors:

     [EAGAIN]           See EWOULDBLOCK, below.

     [EWOULDBLOCK]      The file descriptor is for a socket, is marked ONON-
                        BLOCK, and write would block.  The exact error code
                        depends on the protocol, but EWOULDBLOCK is more com-
                        mon.

     In addition, wwrriitteevv() may return one of the following errors:

     [EDESTADDRREQ]     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.

     [EINVAL]           Iovcnt is less than or equal to 0, or greater than
                        UIOMAXIOV.

     [EINVAL]           One of the iovlen values in the iov array is nega-
                        tive.

     [EINVAL]           The sum of the iovlen values in the iov array over-
                        flows a 32-bit integer.

     [ENOBUFS]          The mbuf pool has been completely exhausted when writ-
                        ing to a socket.

     The ppwwrriittee() call may also return the following errors:

     [EINVAL]           The specified file offset is invalid.

     [ESPIPE]           The file descriptor is associated with a pipe, socket,
                        or FIFO.

LEGACY SYNOPSIS
     ##iinncclluuddee <>
     ##iinncclluuddee <>
     ##iinncclluuddee <>

     These include files are needed for all three functions.

SEE ALSO
     fcntl(2), lseek(2), open(2), pipe(2), select(2), compat(5)

STANDARDS
     The wwrriittee() function call is expected to conform to ISO/IEC 9945-1:1990
     (``POSIX.1'').  The wwrriitteevv() and ppwwrriittee() functions are expected to con-
     form to X/Open Portability Guide Issue 4, Version 2 (``XPG4.2'').

HISTORY     The ppwwrriittee() function call appeared in AT&T System V.4 UNIX.  The
     wwrriitteevv() function call appeared in 4.2BSD.  A wwrriittee() function call
     appeared in Version 6 AT&T UNIX.

BSD                              April 2, 1994                             BSD