PROLOG

       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

       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(3POSIX)