Header
stdarg.h
Prototype
type va_arg(va_list arg_ptr, type);
void va_end(va_list arg_ptr);
void va_start(va_list arg_ptr, prev_parm);
Description
These functions maintain a list of arguments to be accessed within
functions that accept a variable number of arguments (for example
the vprintf function). va_list is a type of variable argument list
defined in stdarg.h. Variable argument lists can be processed by a
function when it does not know the number of arguments being
passed. The va_list array holds information required by va_arg
and va_end. When a called function takes a variable argument list,
it declares the last parameter of type va_list.
va_start is first called to initialize the argument list, for which the
parameter arg_ptr points to the first argument in the va_list.
The other parameter prev_parm is the parameter preceding the first
argument. After a call to va_start, a call to va_arg will evaluate
data type from the location pointed to by arg_ptr and increment
arg_ptr. va_end resets arg_ptr to NULL.
Return Value
va_arg returns the current argument. va_start and va_end
evaluate to void.
Compatibility
DOS Windows 3.x Phar Lap DOSX Win32
Example
/* Example for va_arg
Also demonstrates va_end, va_start
*/
#include <stdlib.h>
#include <stdio.h>
#include <stdarg.h>
void miniprintf(char * formatstr, ...)
{
va_list marker;
int pos = 0;
va_start (marker, formatstr);
while (formatstr[pos])
{
if (formatstr[pos] == '% ')
{
pos++;
switch (formatstr[pos])
{
case 'S' :
case 's' :
printf ("% s", va_arg (marker,
char *));
break;
case 'I' :
case 'i' :
printf ("% d", va_arg (marker,
int));
}
}
else
putchar (formatstr[pos]);
pos++;
}
va_end (marker);
}
void main ()
{
miniprintf (" This is a string: \"% s\"\nAnd
this is an int: (% i)\n",
"String", 12);
}
Output
This is a string: "String"
And this is an int: (12)