#include <iostream>
#include <vector>
#include <regex>
 
int main() {
 const std::regex reg("\\{(.*?)\\}(?![^;])");
 std::smatch match;
 std::string s = "Username={My_{}user};Password={my_pswd}}123}}}kk};Password={my_pswd}}123}";
 std::vector<std::string> results(
	std::sregex_token_iterator(s.begin(), s.end(), reg, 1),
std::sregex_token_iterator());
 for (auto result : results)
 {
 std::cout << result << std::endl;
 }
 
 return 0;
}

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