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

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  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 .

IEEE/The Open Group                  2003                            READV(3P)