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In this book I am currently reading I ran across this:
A class doesn't need a constructor. A default constructor is not needed if the object doesn't need initialization.
Am I correct in inferring from the above that the compiler does not generate a default constructor for the class/structure in some cases? If yes, what are those cases? I will venture and say POD is probably one. Are there any other?
EDIT: I have changed the title as the original title gave the meaning that I asked when was a default constructor not defined instead of asking when does a class not have a constructor at all.
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A constructor that accepts no argument (parameter) is known as default constructor. default constructor is useful when we want to initialize class objects with some initial or default value.
A default constructor is a constructor that either has no parameters, or if it has parameters, all the parameters have default values. If no user-defined constructor exists for a class A and one is needed, the compiler implicitly declares a default parameterless constructor A::A() .
Every time an object is created using the new() keyword, at least one constructor is called. It calls a default constructor if there is no constructor available in the class. In such case, Java compiler provides a default constructor by default.
If no user-declared constructors of any kind are provided for a class type (struct, class, or union), the compiler will always declare a default constructor as an inline public member of its class.
A class doesn't need a constructor. A default constructor is not needed if the object doesn't need initialization.
I think the author is talking about this situation:
some_type some_function () {
POD_type this_is_intentionally_uninitialized;
...
}
Under some circumstances a constructor won't be called, period. As soon as you write a constructor you don't have a POD class, so now the constructor will be called.
Whether it is a good or bad thing to have an object running around that contains random, uninitialized data is a different question entirely.
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