#include <iostream>
#include <iterator>
#include <string>
using namespace std;
 
class substr {
     const std::string & s;
     std::size_t len;
 
     friend std::ostream& operator<<(std::ostream& os, const substr &ss) {
         std::copy(ss.s.begin(), ss.s.begin() + std::min(ss.len, ss.s.size()),
                   std::ostream_iterator<char>(os));
         return os;
     }
public:
     substr(const std::string & s, std::size_t len) : s(s), len(len) {}
};
 
int main() {
	int x = 7;
	string foo = "This is a test!";
	cout << substr(foo, x);
	return 0;
}

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