va_start
Min standard notice:
Header: <cstdarg>
The va_start macro enables access to the variable arguments following the named argument parm_n.
# Declarations
void va_start( std::va_list ap, parm_n );
# Parameters
ap: an object of the va_list typeparm_n: the named parameter preceding the first variable parameter
# Notes
va_start is required to support parm_n with overloaded operator&.
# Example
#include <cstdarg>
#include <iostream>
int add_nums(int count...)
{
int result = 0;
std::va_list args;
va_start(args, count);
for (int i = 0; i < count; ++i)
result += va_arg(args, int);
va_end(args);
return result;
}
int main()
{
std::cout << add_nums(4, 25, 25, 50, 50) << '\n';
}
# Defect reports
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| CWG 273 | C++98 | it was unclear whether va_start is required tosupport parm_ns with overloaded operator& | required |
| LWG 2099 | C++98 | the behavior was undefined if parm_n isdeclared with a function, array, or reference type | the behavior is undefined ifparm_n is of reference type |