'\" te
.\" Copyright (c) 2006, Sun Microsystems, Inc.,  All Rights Reserved.
.\" Copyright 1989 AT&T
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.TH VA_ARG 9F "May 12, 2021"
.SH NAME
va_arg, va_start, va_copy, va_end \- handle variable argument list
.SH SYNOPSIS
.nf
#include <sys/varargs.h>



\fBvoid\fR \fBva_start\fR(\fBva_list\fR \fIpvar\fR, \fB\fR\fIname\fR);
.fi

.LP
.nf
\fBtype\fR \fBva_arg\fR(\fBva_list\fR \fIpvar\fR, \fB\fR\fItype\fR);
.fi

.LP
.nf
\fBvoid\fR \fBva_copy\fR(\fBva_list\fR \fIdest\fR, \fBva_list\fR \fIsrc\fR);
.fi

.LP
.nf
\fBvoid\fR \fBva_end\fR(\fBva_list\fR \fIpvar\fR);
.fi

.SH INTERFACE LEVEL
illumos DDI specific (illumos DDI).
.SH PARAMETERS
.SS "\fBva_start()\fR"
.ne 2
.na
\fB\fIpvar\fR\fR
.ad
.RS 8n
Pointer to variable argument list.
.RE

.sp
.ne 2
.na
\fB\fIname\fR\fR
.ad
.RS 8n
Identifier of rightmost parameter in the function definition.
.RE

.SS "\fBva_arg()\fR"
.ne 2
.na
\fB\fIpvar\fR\fR
.ad
.RS 8n
Pointer to variable argument list.
.RE

.sp
.ne 2
.na
\fB\fItype\fR\fR
.ad
.RS 8n
Type name of the next argument to be returned.
.RE

.SS "\fBva_copy()\fR"
.ne 2
.na
\fB\fIdest\fR\fR
.ad
.RS 8n
Destination variable argument list.
.RE

.sp
.ne 2
.na
\fB\fIsrc\fR\fR
.ad
.RS 8n
Source variable argument list.
.RE

.SS "\fBva_end()\fR"
.ne 2
.na
\fB\fIpvar\fR\fR
.ad
.RS 8n
Pointer to variable argument list.
.RE

.SH DESCRIPTION
This set of macros allows portable procedures that accept variable argument
lists to be written. Routines that have variable argument lists but do not use
the \fBvarargs\fR macros are inherently non-portable, as different machines use
different argument-passing conventions. Routines that accept a variable
argument list can use these macros to traverse the list.
.sp
.LP
\fBva_list\fR is the type defined for the variable used to traverse the list of
arguments.
.sp
.LP
\fBva_start()\fR is called to initialize \fIpvar\fR to the beginning of the
variable argument list. \fBva_start()\fR must be invoked before any access to
the unnamed arguments. The parameter \fIname\fR is the identifier of the
rightmost parameter in the variable parameter list in the function definition
(the one just before the "\fB, .\|.\|.\|\fR"). If this parameter is declared
with the \fBregister\fR storage class or with a function or array type, or with
a type that is not compatible with the type that results after application of
the default argument promotions, the behavior is undefined.
.sp
.LP
\fBva_arg()\fR expands to an expression that has the type and value of the next
argument in the call. The parameter \fIpvar\fR must be initialized by
\fBva_start()\fR. Each invocation of \fBva_arg()\fR modifies \fIpvar\fR so that
the values of successive arguments are returned in turn. The parameter
\fItype\fR is the type name of the next argument to be returned. The type name
must be specified in such a way that the type of pointer to an object that has
the specified type can be obtained by postfixing a \fB*\fR to \fItype\fR. If
there is no actual next argument, or if \fBtype\fR is not compatible with the
type of the actual next argument (as promoted according to the default argument
promotions), the behavior is undefined.
.sp
.LP
The \fBva_copy()\fR macro saves the state represented by the
\fBva_list\fR \fIsrc\fR in the \fBva_list\fR \fIdest\fR. The \fBva_list\fR
passed as \fIdest\fR should not be initialized by a previous call to
\fBva_start()\fR. It then must be passed to \fBva_end()\fR before being reused
as a parameter to \fBva_start()\fR or as the \fIdest\fR parameter of a
subsequent call to \fBva_copy()\fR. The behavior is undefined if any of these
restrictions are not met.
.sp
.LP
The \fBva_end()\fR macro is used to clean up. It invalidates \fIpvar\fR for use
(unless \fBva_start()\fR is invoked again).
.sp
.LP
Multiple traversals, each bracketed by a call to \fBva_start()\fR and
\fBva_end()\fR, are possible.
.SH EXAMPLES
\fBExample 1 \fRCreating a Variable Length Command
.sp
.LP
The following example uses these routines to create a variable length command.
This might be useful for a device that provides for a variable-length command
set. \fBncmdbytes\fR is the number of bytes in the command. The new command is
written to \fBcmdp\fR.

.sp
.in +2
.nf
static void
xx_write_cmd(uchar_t *cmdp, int ncmdbytes, ...)
{
        va_list ap;
        int     i;

        /*
         * Write variable-length command to destination
         */
        va_start(ap, ncmdbytes);
        for (i = 0; i < ncmdbytes; i++) {
                *cmdp++ = va_arg(ap, uchar_t);
        }
        va_end(ap);
}
.fi
.in -2

.SH SEE ALSO
.BR vcmn_err (9F),
.BR vsprintf (9F)
.SH NOTES
It is up to the calling routine to specify in some manner how many arguments
there are, since it is not always possible to determine the number of arguments
from the stack frame.
.sp
.LP
Specifying a second argument of \fBchar\fR or \fBshort\fR to \fBva_arg\fR makes
your code non-portable, because arguments seen by the called function are not
\fBchar\fR or \fBshort\fR. C converts \fBchar\fR and \fBshort\fR arguments to
\fBint\fR before passing them to a function.