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be an abstract data type. To save space, the rest of Listing 18.3 is not reproduced here. Replace the declaration of Shape in Listing 18.3, lines 514, with the declaration of Shape in Listing 18.4 and run the program again. |
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LISTING 18.4 ABSTRACT DATA TYPES |
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1: class Shape
2: {
3: public:
4: Shape(){}
5: virtual ~Shape(){}
6: virtual long GetArea() = 0;
7: virtual long GetPerim()= 0;
8: virtual void Draw() = 0;
9: private:
10: }; |
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(1)Circle (2)Rectangle (3)Square (0)Quit:2
× × × × × ×
× × × × × ×
× × × × × ×
× × × × × ×
(1)Circle (2)Rectangle (3)Square (0)Quit:3
× × × × ×
× × × × ×
× × × × ×
× × × × ×
× × × × ×
(1)Circle (2)Rectangle (3)Square (0)Quit:0 |
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Analysis: As you can see, the workings of the program are totally unaffected. The only difference is that it is now impossible to make an object of class Shape. |
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ABSTRACT DATA TYPES
You declare a class to be an abstract data type by including one or more pure virtual functions in the class declaration. Declare a pure virtual function by writing = 0 after the function declaration. |
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| | For example: | |
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class Shape
{
virtual void Draw() = 0; // pure virtual
}; |
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