How to Use a Member Variable as a Default Argument in C Member Functions?

Using a Member Variable as a Default Argument in C

When crafting member functions in C , it's often desirable to make certain arguments optional and use a member variable as a default value. However, this can trigger compilation errors if the member variable is not static.

Consider the following code snippet:

class Object
{
public:
    void MoveTo(double speed, Point position);

protected:
    Point initPos;
    Point currPos;
};

void Object::MoveTo(double speed, Point position = initPos)
{
    currPos = postion;
}

Attempting to compile this code will result in the error message: "invalid use of non-static data member 'Object::initPos'". This occurs because default argument expressions cannot depend on non-class members.

To resolve this issue, you need to employ two overloads of the MoveTo method:

void Object::MoveTo(double speed)
{
    MoveTo(speed, initPos);
}

void Object::MoveTo(double speed, Point position)
{
    currPos = postion;
}

The single-argument method calls the two-argument method, passing in the default value. This allows for a single implementation of MoveTo while maintaining the desired functionality of using a member variable as a default.

By adhering to these techniques, you can effectively utilize member variables as default arguments in C member functions without facing compilation errors.

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