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WRITESTRING(This is a string); |
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the precompiler will turn it into this: |
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cout << This is a string; |
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Note that the string This is a string is put into quotes, as required by cout. |
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The concatenation operator enables you to bond together more than one term into a new word. The new word is actually a token that can be used as a class name, a variable name, an offset into an array, or anywhere else a series of letters might appear. |
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Assume for a moment that you have five functions, named fOnePrint, fTwoPrint, fThreePrint, fFourPrint, and fFivePrint. You can then declare |
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#define fPrint(x) f ## x ## Print |
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and then use it with fPRINT(Two) to generate fTwoPrint, and with fPRINT(Three) to generate fThreePrint. |
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At the conclusion of Hour 19, Linked Lists, a PartsList class was developed. This list could only handle objects of type List. Let's say that this list works well, and you'd like to be able to make lists of animals, cars, computers, and so on. |
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One approach would be to create AnimalList, CarList, ComputerList, and so forth, cutting and pasting the code in place. This would quickly become a nightmare, because every change to one list would have to be written to all the others. |
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An alternative is to use macros and the concatenation operator. For example, you could define |
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#define Listof(Type) class Type##List \
{ \
public: \
Type##List(){} \
private: \
int itsLength; \
}; |
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This example is overly sparse, but the idea would be to put in all the necessary methods and data. When you were ready to create an AnimalList, you would write |
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