Question

I was given a c++ main and have to code it so it works.

I am having some trouble understanding the code as I am a bit new to cpp.

Here is the code

int main(int argc, char *argv[]) {
  Class::setAtribute("string"); 
  Class(Class::CONSTANT) << "starting up..."; 
}

Some questions:

1. How can the first line work with no variables? Is it static?

2. The second line is really strange for me, what I can make out is a Constructor that takes in a class constante and then prints it out somehow?

   If someone could explain me this bit of code it would be great!

   Thanks in advance.

Answer 1

How can the first line work with no variables? Is it static?

Class::setAtribute() must be a static function in class Class. A static function doesn’t need an instance of a class (object).

The second line is really strange for me, what I can make out is a Constructor that takes in a class constante and then prints it out somehow?

Right, it constructs an instance of Class passing Class::CONSTANT as the argument to Class constructor. For Class(Class::CONSTANT) << "starting up..."; to compile there must be an overloaded operator<< in the form of:

As a member function of Class (David Rodríguez – dribeas):

<some_return_value_type> Class::operator<<(char const*);

or as a free-standing function:

<some_return_value_type> operator<<(Class const&, char const*);

or:

<some_return_value_type> operator<<(Class const&, std::string const&);

or, in C++11:

<some_return_value_type> operator<<(Class&&, char const*);

The second argument, in fact, can be anything that can be constructed from a string literal char const[]. Or, alternatively, Class can have a conversion operator to, say, std::ostream&, so that std::ostream& std::operator<<(std::ostream&, char const*) is picked instead. Looking at Class definition and free-standing functions in its namespace must yield a definite answer.