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

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 Technol-
       ogy -- 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(P)