Question

Given the following classes:

class foo
{
private:
    int c;

public:
    foo( int a = 42 ) { c = a; }
    ~foo();
};

class bar: public foo
{
public:
    bar();
    ~bar();
};

How can I make bar override c with a different number? Can I do something like this?

bar::bar() 
{
    c = 12;
}

I get this error when trying to compile:

test.cpp: In constructor ‘bar::bar()’:
test.cpp:8:7: error: ‘int foo::c’ is private

Answer 1

Call your base class’ constructor in the constructor initialization list:

bar::bar()
  : foo(12)
{ }

Incidentally, you should always prefer using a constructor initialization list over assignment inside the constructor body, so your foo constructor would be better written as:

foo( int a = 42 ) : c(a) { }