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you invoke the constructor for Cat that takes one parameter (in this case, the value 5). If, however, you write |
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the compiler allows you to leave the parentheses off and calls the default constructor, the constructor that takes no parameters. |
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Constructors Provided by the Compiler |
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If you declare no constructors at all, the compiler will create a default constructor for you. (Remember, the default constructor is the constructor that takes no parameters.) |
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The default constructor the compiler provides takes no action; it is as if you had declared a constructor that took no parameters and whose body was empty. |
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There are two important points to note about this: |
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The default constructor is any constructor that takes no parameters, whether you declare it or you get it for free from the compiler. |
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If you declare any constructor (with or without parameters), the compiler will not provide a default constructor for you. In that case, if you want a default constructor, you must declare it yourself. |
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If you fail to declare a destructor, the compiler will also give you one of those, and this too will have an empty body and will do nothing. |
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As a matter of form, if you declare a constructor, be sure to declare a destructor, even if your destructor does nothing. Although it is true that the default destructor would work correctly, it doesn't hurt to declare your own, and it makes your code clearer. |
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Listing 6.2 rewrites the Cat class to use a constructor to initialize the Cat object, setting its age to whatever initial age you provide. It also demonstrates where the destructor is called. |
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LISTING 6.2 USING CONSTRUCTORS AND DESTRUCTORS |
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1: // Demonstrates declaration of a constructor and
2: // destructor for the Cat class
3:
4: #include <iostream.h> // for cout
5:
6: class Cat // begin declaration of the class
7: {
8: public: // begin public section
9: Cat(int initialAge); // constructor |
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continues |
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