what is visibility and scope

[kannan.ganesh]

What is visibility and scope? what are difference between them?

[John E]

'scope' usually refers to the lifetime of a variable (the time between it getting created and destroyed). 'visibility' refers to whether or not it's accessible. However, it's not quite as simple as that because local variables can hide variables of the same name that were previously visible and in scope. For example:-

class myClass
{
public:
    myClass(); // c'tor
    int publicInt;

private:
    int privateInt;
};

// Somewhere in your code
myClass myObj;

    myObj.publicInt = 3; // Acceptable - 'publicInt' is public - therefore visible
    myObj.privateInt = 3; // 'privateInt' is private - it remains in scope for the duration of 'myObj' but is not visible from outside the object



// Another example
myClass::SomeFunc()
{
int x;

    publicInt = 9; // refers to the member variable

    if (something_or_other)
    {
        int publicInt = 3; // This new declaration hides the member variable temporarily

        // Within the scope of these 2 brackets, 'publicInt' refers to the
        // local declaration. Member 'publicInt' is temporarily hidden.

        x = publicInt; // 'x' will equal 3
    }

    x = publicInt; // 'x' will equal 9
}