PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

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

       readv — read a vector

SYNOPSIS         top

       #include <sys/uio.h>

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

DESCRIPTION         top

       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         top

       Refer to read(3p).

ERRORS         top

       Refer to read(3p).

       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         top

   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         top

       None.

RATIONALE         top

       Refer to read(3p).

FUTURE DIRECTIONS         top

       None.

SEE ALSO         top

       read(3p), writev(3p)

       The Base Definitions volume of POSIX.1‐2008, sys_uio.h(0p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The Open
       Group Base Specifications Issue 7, Copyright (C) 2013 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
       applied.) 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.unix.org/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                 2013                           READV(3P)

Pages that refer to this page: sys_uio.h(0p)read(3p)writev(3p)