I want to have a class like below:
Class Test {
Test();
~Test();
...
}
I want to be able to use following statement:
std::string str;
Test t;
str = t;
what should I do? should I override to_string? If yes it seems that it is not possible to inherit from std::string class. Or I have to override special operator? What about Pointer assignment? like below:
std::string str;
Test* t = new Test();
str = t;
You can provide a user-defined conversion operator to std::string:
class Test {
//...
public:
operator std::string () const {
return /*something*/;
}
};
This will allow a Test object to be implicitly-converted to a std::string.
Test::operator std::string() const just my 2c
std::string tmp = my_test; doSomething(&tmp);Although in C++ it is possible, it is generally not advised to inherit from standard classes, see Why should one not derive from c++ std string class? for more info.
I am wondering, what is the function of the assignment of
str = t;
str is a std::string type, t is Test type. So what is the expected value of the assigment? No one can guess. I suggest to explicitly call a conversion method or an operator for code clarity.
This would make your example look like:
str = t.convertToString();
or the more standard way is to implement the stream operator, which makes
str << t;
(Note this example works if str is a stream type, if it is a string, you need further code, see C++ equivalent of java.toString?.)
But, if you really want it to work without a conversion method, you can override the string assignment operator of Test:
class Test {
public:
operator std::string() const { return "Hi"; }
}
See also toString override in C++
Although this is a perfect solution to your question, it may come with unforeseen problems on the long run, as detailed in the linked article.
str = static_cast<std::string>(t); which is probably safer, even if it is more characters.