Shulou(Shulou.com)05/31 Report--

This article mainly introduces the relevant knowledge of what is the principle of the C++ second-order construction pattern and how to use it. The content is detailed and easy to understand, easy to operate, and has a certain reference value. I believe you will gain something after reading this C++ second-order construction pattern principle and how to use it. Let's take a look.

I. Review of constructors

About the constructor

The constructor of the class is used for object initialization

The constructor has the same name as the class and has no return value

The constructor is automatically called when the object is defined

problem

How to judge the execution result of the constructor?

What happens when the return statement is executed in the constructor?

Does the end of constructor execution mean that the object was constructed successfully?

Let's look at the constructor of an exception:

# include class Test {int mi; int mj; bool mStatus;public: Test (int I, int j): mStatus (false) {mi = i; return; mj = j; mStatus = true;} int getI () {return mi;} int getJ () {return mj;} int status () {return mStatus }; int main () {Test T1 (1,2); if (t1.status ()) {printf ("t1.mi =% d\ n", t1.getI ()); printf ("t1.mj =% d\ n", t1.getJ ());} return 0;}

The running result is as follows. As you can see, if there is no output, it ends when you encounter the return constructor:

Constructor function

Only provide the opportunity to initialize member variables automatically

There is no guarantee that the initialization logic will succeed

The constructor ends immediately after executing the return statement

Conclusion: the constructor can determine only the initial state of the object, not the birth of the object!

II. Objects of semi-finished products

The concept of semi-finished object

The object that the initialization operation cannot complete as expected

Semi-finished products are legitimate C++ objects and an important source of Bug.

Let's take a look at the harm of a semi-finished object:

IntArray.h:

# ifndef _ INTARRAY_H_#define _ INTARRAY_H_class IntArray {private: int masked pooling; int* massively pointering public: IntArray (int len); IntArray (const IntArray& obj); int length (); bool get (int index, int& value); bool set (int index, int value); ~ IntArray ();}; # endif

IntArray.c:

(note: m_pointer = 0; / / assume that m_pointer is a null pointer, which is used to simulate a failure to apply for memory)

# include "IntArray.h" IntArray::IntArray (int len) {m_pointer = 0; / / assume that m_pointer is a null pointer and is used to simulate a failed application for memory if (m_pointer) {for (int item0; I)

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