I find following boost code

```
        for (auto entry : boost::make_iterator_range(boost::filesystem::directory_iterator(dir_path), {})) {
            std::cout << entry << std::endl;
        }

```

entry can be output with dir path, I guess c++ has feature like java Class#toString to custom output string, I try following code:

```
class C {
    str to_string() {
        return "prpr";
    }
};

TEST_F(FileTest, Draft1) {
    C c;
    std::cout << c << std::endl;
}

```

I expect output "prpr", but it doesn't work, how to fix it?