C + + Learning Note Constructor (a) default constructor

Definition: The constructor used to create an object when an explicit initial value is not provided.

Example:

Class TestClass

{

Private

int m_a;

int m_b;

Public

TestClass (); Default constructor 1

TestClass (int a,int b); constructor function

TestClass (int a=10,int b=5); Default constructor 2

};//Note that the actual use of a class in the default constructor 1 and the default constructor 2 can only appear 1, here just to illustrate

Summarize:

1) The default constructor is primarily used to complete the initialization of this form: TestClass A; In this case, if the programmer does not define a default constructor, the compiler will make an error.

2) If the programmer does not provide any constructors, then the compiler will automatically generate a default constructor.

3) There are two ways to define a default constructor, one of which is the default constructor 1 in the example above, a parameterless constructor, and the default constructor 2 in the example above, which defines a constructor where all formal parameters have default values.

4) A class can have only one default constructor.

5) If the programmer provides any form of constructor, then the compiler will no longer provide a default constructor.

C + + Learning Note Constructor (a) default constructor