<sys/uio.h>(0P)                                     POSIX Programmer's Manual                                    <sys/uio.h>(0P)



NAME
       sys/uio.h - definitions for vector I/O operations

SYNOPSIS
       #include <sys/uio.h>

DESCRIPTION
       The <sys/uio.h> header shall define the iovec structure that includes at least the following members:


              void   *iov_base  Base address of a memory region for input or output.
              size_t  iov_len   The size of the memory pointed to by iov_base.

       The <sys/uio.h> header uses the iovec structure for scatter/gather I/O.

       The ssize_t and size_t types shall be defined as described in <sys/types.h>.

       The following shall be declared as functions and may also be defined as macros. Function prototypes shall be provided.


              ssize_t readv(int, const struct iovec *, int);
              ssize_t writev(int, const struct iovec *, int);

       The following sections are informative.

APPLICATION USAGE
       The  implementation can put a limit on the number of scatter/gather elements which can be processed in one call. The sym-
       bol {IOV_MAX} defined in <limits.h> should always be used to learn about the limits instead of assuming a fixed value.

RATIONALE
       Traditionally, the maximum number of scatter/gather elements the system can process in one call  were  described  by  the
       symbolic  value {UIO_MAXIOV}. In IEEE Std 1003.1-2001 this value is replaced by the constant {IOV_MAX} which can be found
       in <limits.h>.

FUTURE DIRECTIONS
       None.

SEE ALSO
       <limits.h>, <sys/types.h>, the System Interfaces volume of IEEE Std 1003.1-2001, read(), write()

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, Copy-
       right (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.open-
       group.org/unix/online.html .



IEEE/The Open Group                                           2003                                               <sys/uio.h>(0P)