Member Initialization

In C++, all constructors must initialize all primitive types. A C++ constructor does not need to initialize any object members (like string or vector).

This is exactly the opposite from Java, where you must initialize all of the object instance variables, or they are set to null (an invalid object). In Java, all primitive instance variables are automatically initialized to 0 like this:

public class Point
{
    private String name;
    int x, y;
    public Point() {}
}

Point p = new Point(); // x,y->0, name is null (invalid)

In C++, if you fail to initialize a primitive data member, then it assumes whatever random value was in memory; if you don't initialize an object, such as string or vector, its default constructor will automatically run, and it is still a valid object.

class Point
{
public:
    Point() {}
private:
    string name;
    int x, y;
};

Point p; // x,y->random, name is valid empty string

Of course, if you provide in-definition initializers for your primitive data members, they will automatically be initialized, even if your construct does not explicitly initialize them.

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