va_arg(9F) Kernel Functions for Drivers va_arg(9F)NAME
va_arg, va_start, va_copy, va_end - handle variable argument list
SYNOPSIS
#include <sys/varargs.h>
void va_start(va_list pvar, name);
(type *) va_arg(va_list pvar, type);
void va_copy(va_list dest, va_list src);
void va_end(va_list pvar);
INTERFACE LEVEL
Solaris DDI specific (Solaris DDI).
PARAMETERSva_start()
pvar Pointer to variable argument list.
name Identifier of rightmost parameter in the func‐
tion definition.
va_arg()
pvar Pointer to variable argument list.
type Type name of the next argument to be returned.
va_copy()
dest Destination variable argument list.
src Source variable argument list.
va_end()
pvar Pointer to variable argument list.
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 varargs 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.
va_list is the type defined for the variable used to traverse the list
of arguments.
va_start() is called to initialize pvar to the beginning of the vari‐
able argument list. va_start() must be invoked before any access to the
unnamed arguments. The parameter name is the identifier of the right‐
most parameter in the variable parameter list in the function defini‐
tion (the one just before the ", ..."). If this parameter is declared
with the register 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 unde‐
fined.
va_arg() expands to an expression that has the type and value of the
next argument in the call. The parameter pvar must be initialized by
va_start(). Each invocation of va_arg() modifies pvar so that the val‐
ues of successive arguments are returned in turn. The parameter type 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 * to type. If
there is no actual next argument, or iftype is not compatible with the
type of the actual next argument (as promoted according to the default
argument promotions), the behavior is undefined.
The va_copy() macro saves the state represented by the va_listsrc in
the va_list dest. The va_list passed as dest should not be initialized
by a previous call to va_start() It then must be passed to va_end()
before being reused as a parameter to va_start() or as the dest parame‐
ter of a subsequent call to va_copy(). The behavior is undefined if any
of these restrictions are not met.
The va_end() macro is used to clean up. It invalidates pvar for use
(unless va_start() is invoked again).
Multiple traversals, each bracketed by a call to va_start() and
va_end(), are possible.
EXAMPLES
Example 1: Creating a Variable Length Command
The following example uses these routines to create a variable length
command. This might be useful for a device that provides for a vari‐
able-length command set. ncmdbytes is the number of bytes in the com‐
mand. The new command is written to cmdp.
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);
}
SEE ALSOvcmn_err(9F), vsprintf(9F)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.
Specifying a second argument of char or short to va_arg makes your code
non-portable, because arguments seen by the called function are not
char or short. C converts char and short arguments to int before pass‐
ing them to a function.
SunOS 5.10 22 Mar 2006 va_arg(9F)
