writev(3p) — Linux manual page


WRITEV(3P)              POSIX Programmer's Manual             WRITEV(3P)

PROLOG         top

       This manual page is part of the POSIX Programmer's Manual.  The
       Linux implementation of this interface may differ (consult the
       corresponding Linux manual page for details of Linux behavior),
       or the interface may not be implemented on Linux.

NAME         top

       writev — write a vector

SYNOPSIS         top

       #include <sys/uio.h>

       ssize_t writev(int fildes, const struct iovec *iov, int iovcnt);

DESCRIPTION         top

       The writev() function shall be equivalent to write(), except as
       described below. The writev() function shall gather output data
       from the iovcnt buffers specified by the members of the iov
       array: iov[0], iov[1], ..., iov[iovcnt-1].  The iovcnt argument
       is valid if greater than 0 and less than or equal to {IOV_MAX},
       as defined in <limits.h>.

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

       If fildes refers to a regular file and all of the iov_len members
       in the array pointed to by iov are 0, writev() shall return 0 and
       have no other effect. For other file types, the behavior is

       If the sum of the iov_len values is greater than {SSIZE_MAX}, the
       operation shall fail and no data shall be transferred.

RETURN VALUE         top

       Upon successful completion, writev() shall return the number of
       bytes actually written. Otherwise, it shall return a value of -1,
       the file-pointer shall remain unchanged, and errno shall be set
       to indicate an error.

ERRORS         top

       Refer to write(3p).

       In addition, the writev() function shall fail if:

       EINVAL The sum of the iov_len values in the iov array would
              overflow an ssize_t.

       The writev() function may fail and set errno to:

       EINVAL The iovcnt argument was less than or equal to 0, or
              greater than {IOV_MAX}.

       The following sections are informative.

EXAMPLES         top

   Writing Data from an Array
       The following example writes data from the buffers specified by
       members of the iov array to the file associated with the file
       descriptor fd.

           #include <sys/types.h>
           #include <sys/uio.h>
           #include <unistd.h>
           ssize_t bytes_written;
           int fd;
           char *buf0 = "short string\n";
           char *buf1 = "This is a longer string\n";
           char *buf2 = "This is the longest string in this example\n";
           int iovcnt;
           struct iovec iov[3];

           iov[0].iov_base = buf0;
           iov[0].iov_len = strlen(buf0);
           iov[1].iov_base = buf1;
           iov[1].iov_len = strlen(buf1);
           iov[2].iov_base = buf2;
           iov[2].iov_len = strlen(buf2);
           iovcnt = sizeof(iov) / sizeof(struct iovec);

           bytes_written = writev(fd, iov, iovcnt);



RATIONALE         top

       Refer to write(3p).



SEE ALSO         top

       readv(3p), write(3p)

       The Base Definitions volume of POSIX.1‐2017, limits.h(0p),

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic
       form from IEEE Std 1003.1-2017, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The
       Open Group Base Specifications Issue 7, 2018 Edition, Copyright
       (C) 2018 by the Institute of Electrical and Electronics
       Engineers, Inc and The Open Group.  In the event of any
       discrepancy between this version and the original IEEE and The
       Open Group Standard, the original IEEE and The Open Group
       Standard is the referee document. The original Standard can be
       obtained online at http://www.opengroup.org/unix/online.html .

       Any typographical or formatting errors that appear in this page
       are most likely to have been introduced during the conversion of
       the source files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group               2017                        WRITEV(3P)

Pages that refer to this page: sys_uio.h(0p)readv(3p)write(3p)