How to initialize static class objects in c++?

Question

Lane.h

class Lane{
    //other declarations..
public:
    Lane(){}
    static Lane left_line;
    static Lane right_line;
};

Lane.cpp

Lane Lane::left_line;

main.cpp

int main(){
    Lane::left_line();  //doesn't work

What am I doing wrong or am I doing everything wrong. I am actually confused about how the static objects work exactly.

Answer 1

static members get declared inside a class and initialized once outside the class. There is no need to call the constructor once again. I've added a method to your Lane class to make it clearer.

class Lane{
    //other declarations..
public:
    Lane(){}
    static Lane left_line; //<declaration
    static Lane right_line;

   void use() {};
};

Lane.cpp

Lane Lane::left_line; //< initialisation, calls the default constructor of Lane

main.cpp

int main() {
  // Lane::left_line(); //< would try to call a static function called left_line which does not exist
  Lane::left_line.use(); //< just use it, it was already initialised
}

You can make the initialisation even more obvious by doing this:

Lane Lane::left_line = Lane();

in Lane.cpp.