std::optional

 1 #include <iostream>
 2 #include <optional>
 3 #include <string>
 4 
 5 std::optional<std::string> create(bool b)
 6 {
 7     if(b) return "Godzilla";
 8     return {};
 9 }
10 
11 int main()
12 {
13     std::cout << "create(false) return: " << create(false).value_or("empty") << std::endl;
14     std::cout << "create(true) return: " << create(true).value_or("empty") << std::endl;
15     return 0;
16 }

输出：

create(false) return: empty
create(true) return: Godzilla