toString override in C++ [duplicate]

Question

In Java, when a class overrides .toString() and you do System.out.println() it will use that.

class MyObj {     public String toString() { return "Hi"; } } ... x = new MyObj(); System.out.println(x); // prints Hi 

How can I accomplish that in C++, so that:

Object x = new Object(); std::cout << *x << endl; 

Will output some meaningful string representation I chose for Object?

Answer 1

std::ostream & operator<<(std::ostream & Str, Object const & v) {    // print something from v to str, e.g: Str << v.getX();   return Str; } 

If you write this in a header file, remember to mark the function inline: inline std::ostream & operator<<(... (See the C++ Super-FAQ for why.)

Answer 2

Alternative to Erik's solution you can override the string conversion operator.

class MyObj { public:     operator std::string() const { return "Hi"; } } 

With this approach, you can use your objects wherever a string output is needed. You are not restricted to streams.

However this type of conversion operators may lead to unintentional conversions and hard-to-trace bugs. I recommend using this with only classes that have text semantics, such as a Path, a UserName and a SerialCode.