.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 
.TH "<sys/uio.h>" 0P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\" <sys/uio.h> 
.SH NAME
sys/uio.h \- definitions for vector I/O operations
.SH SYNOPSIS
.LP
\fB#include <sys/uio.h> \fP
.SH DESCRIPTION
.LP
The \fI<sys/uio.h>\fP header shall define the \fBiovec\fP structure
that includes at least the following members:
.sp
.RS
.nf

\fBvoid   *iov_base \fP Base address of a memory region for input or output. \fB
size_t  iov_len  \fP The size of the memory pointed to by \fIiov_base.\fP \fB
\fP
.fi
.RE
.LP
The \fI<sys/uio.h>\fP header uses the \fBiovec\fP structure for scatter/gather
I/O.
.LP
The \fBssize_t\fP and \fBsize_t\fP types shall be defined as described
in \fI<sys/types.h>\fP.
.LP
The following shall be declared as functions and may also be defined
as macros. Function prototypes shall be provided.
.sp
.RS
.nf

\fBssize_t readv(int, const struct iovec *, int);
ssize_t writev(int, const struct iovec *, int);
\fP
.fi
.RE
.LP
\fIThe following sections are informative.\fP
.SH APPLICATION USAGE
.LP
The implementation can put a limit on the number of scatter/gather
elements which can be processed in one call. The symbol
{IOV_MAX} defined in \fI<limits.h>\fP should always be used to learn
about the
limits instead of assuming a fixed value.
.SH RATIONALE
.LP
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 \fI<limits.h>\fP.
.SH FUTURE DIRECTIONS
.LP
None.
.SH SEE ALSO
.LP
\fI<limits.h>\fP, \fI<sys/types.h>\fP, the System Interfaces volume
of IEEE\ Std\ 1003.1-2001, \fIread\fP(), \fIwrite\fP()
.SH 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 .