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 correspond-
       ing 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 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(3P)