What does : mean?

I have 2 classes:

class base {
    virtual void foo() {};
};

class derived : public base {
    void foo() { base::foo(); }
};

I made a mistake and wrote base:foo(); instead of base::foo();. The code was compiled and run, but segfaulted.

I don't know how I can Google it and don't know what it is, but I'm very interested: what does that mean?

base:foo();

If it is important:

class base : public QAbstractGraphicsShapeItem

void foo() { base:foo(); }

is equivalent to:

void foo()
{
   base: // An unused label.
   foo(); // Calls the function again, resulting in infinite recursion.
}

Due to infinite recursion, the function causes stack overflow.

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