std::sub_match<BidirIt>::swap

#include <cassert>
#include <iostream>
#include <regex>
 
int main()
{
 const char* s = "Quick red cat";
 std::sub_match <const char*> x, y;
 
 x.first = &s[0];
 x.second = &s[5];
 x.matched = false;
 
 y.first = &s[012];
 y.second = &s[13];
 y.matched = true;
 
 std::cout << "Before swap:\n";
 std::cout << "x.str() = [" << x.str() << "]\n";
 std::cout << "y.str() = [" << y.str() << "]\n";
 assert (!x.matched and y.matched);
 
 x.swap(y);
 
 std::cout << "After swap:\n";
 std::cout << "x.str() = [" << x.str() << "]\n";
 std::cout << "y.str() = [" << y.str() << "]\n";
 assert (x.matched and !y.matched);
}

Before swap:
x.str() = []
y.str() = [cat]
After swap:
x.str() = [cat]
y.str() = []