READV(3)                   POSIX Programmer's Manual                  READV(3)



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

NAME
       readv -- read a vector

SYNOPSIS
       #include <sys/uio.h>

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

DESCRIPTION
       The readv() function shall be equivalent to read(), except as described
       below. The readv() function shall place the input data into 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}.

       Each iovec entry specifies the base address and length of an area in
       memory where data should be placed. The readv() function shall always
       fill an area completely before proceeding to the next.

       Upon successful completion, readv() shall mark for update the last data
       access timestamp of the file.

RETURN VALUE
       Refer to read().

ERRORS
       Refer to read().

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

       EINVAL The sum of the iov__len values in the iov array overflowed an
              ssize_t.

       The readv() function may fail if:

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

       The following sections are informative.

EXAMPLES
   Reading Data into an Array
       The following example reads data from the file associated with the file
       descriptor fd into the buffers specified by members of the iov array.


           #include <sys/types.h>
           #include <sys/uio.h>
           #include <unistd.h>
           ...
           ssize_t bytes_read;
           int fd;
           char buf0[20];
           char buf1[30];
           char buf2[40];
           int iovcnt;
           struct iovec iov[3];

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

           bytes_read = readv(fd, iov, iovcnt);
           ...

APPLICATION USAGE
       None.

RATIONALE
       Refer to read().

FUTURE DIRECTIONS
       None.

SEE ALSO
       read(), writev()

       The Base Definitions volume of POSIX.1-2017, <sys_uio.h>

COPYRIGHT
       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                             READV(3)
