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 st_atime field 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 IEEE Std 1003.1-2001, <sys/uio.h>

COPYRIGHT

       Portions  of  this  text  are  reprinted  and  reproduced in electronic form from IEEE Std
       1003.1, 2003 Edition, Standard for Information Technology  --  Portable  Operating  System
       Interface  (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 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 .