Interview Question: Casting in C++

Sample Question #173 (programming – C++)

Consider the following class definitions in C++:

class Computer {
   …
};

class Laptop : public Computer {
   …
};

Computer sony;
Laptop vaio;

You may assume both Computer and Laptop are well-defined.

What’s wrong with the following two assigments?

1. Computer * pC = &vaio;

2. Laptop * pL = &sony;

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One Response to Interview Question: Casting in C++

  1. Brett says:

     ANSWER
     
    1. This is implicit upcasting; it’s fine.
     
    2. This is implicit downcasting, and it’s not allowed in C++. An explicit cast must be used:
            Laptop * pL = (Laptop *) &sony;
     

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