Difference between revisions of "cpp/utility/variadic/va start"

Revision as of 02:12, 26 October 2023

The va_start macro enables access to the variable arguments following the named argument parm_n.

va_start should be invoked with an instance to a valid va_list object ap before any calls to va_arg.

If parm_n is declared with reference type or with a type not compatible with the type that results from default argument promotions, the behavior is undefined.

Parameters

Expanded value

(none)

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';
}

150

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

See also