C++学习笔记之 构造函数的初始化列表

<span style="font-family: Arial, Helvetica, sans-serif;">// 20160220 note</span>

/*
知识点：构造函数的初始化列表
1.根据构造函数的调用规则 设计A的构造函数必须要使用！！！如果在B的类中定义了A的对象，就必须要调用A的构造函数进行初始化。
语法： Constructor::Constructor():a1(m),a2(n),a3(v1,v2)...
2.先执行 被组合对象的构造函数，也就是该例子中的A类的对象
如果组合对象有多个，则按照定义的顺序，而不是按照初始化列表的顺序来执行
析构函数的顺序和构造函数调用顺序相反
*/

#include "stdafx.h"
#include <iostream>

using namespace std;
class A{
public:
A(int _a){
a = _a;
cout << "执行A构造函数" << endl;
}
~A(){
cout << "执行A析构函数" << endl;
}
private:
int a;
};
class B{
public:
B(int _b1,int _b2):a1(1),a2(2){
cout << "执行B构造函数" << endl;
b1 = _b1;
b2 = _b2;
}
B(int x, int y, int m, int n):a1(m),a2(n){
b1 = x;
b2 = y;
cout << "执行B构造重载函数" << endl;
}
~B(){
cout << "执行B析构函数" << endl;
}
private:
int b1;
int b2;
A a1;
A a2;
};
void playObjB(){
B b(1, 2, 3, 4);
}
int _tmain(int argc, _TCHAR* argv[])
{
playObjB();
return 0;
}

// 构造和析构函数综合练习.cpp : 定义控制台应用程序的入口点。
#include <iostream>

using namespace std;
class ABCD{
public:
ABCD(int a,int b,int c,int d){
this->a = a;
this->b = b;
this->c = c;
this->d = d;
cout << endl;
cout << "调用ABCD构造函数" << endl;
cout << "this->a:" << this->a << " " << "this->b:" << this->b << " "
"this->c:" << this->c << " ""this->d:" << this->d << " ";
}
~ABCD(){
cout << endl;
cout << "调用ABCD析构函数" << endl;
}
int getA(){
return this->a;
}
private:
int a;
int b;
int c;
int d;
};
class MyE{
public:
MyE() :abcd1(1, 2, 3, 4), abcd2(5, 6, 7, 8), m(10){
cout << endl;
cout << "MyE构造函数调用" << endl;
}
~MyE(){
cout << endl;
cout << "MyE构造函数调用" << endl;
}
MyE(const MyE&obj) :abcd1(11, 12, 13, 14), abcd2(15, 16, 17, 18), m(20){
cout << endl;
cout << "MyE拷贝构造函数调用" << endl;
}
int getM(){
return m;
}
private:
ABCD abcd1;
ABCD abcd2;
const int m;
};
void doThing(MyE mye1){
cout << endl;
cout << "doThing myE" << endl;
cout << mye1.getM() << endl;
}
int run(){
printf("run() start\n");
MyE mye;
doThing(mye);//此时用实参赋值给形参，会调用myE类的拷贝构造函数
printf("run() end\n");
return 0;
}
int _tmain(int argc, _TCHAR* argv[])
{
run();
return 0;
}

// 构造和析构函数综合练习.cpp : 定义控制台应用程序的入口点。
//

#include "stdafx.h"
#include <iostream>

using namespace std;
class ABCD{
public:
ABCD(int a,int b,int c,int d){
this->a = a;
this->b = b;
this->c = c;
this->d = d;
cout << endl;
cout << "调用ABCD构造函数" << endl;
cout << "this->a:" << this->a << " " << "this->b:" << this->b << " "
"this->c:" << this->c << " ""this->d:" << this->d << " ";
}
~ABCD(){
cout << endl;
cout << "调用ABCD析构函数" << endl;
}
int getA(){
return this->a;
}
private:
int a;
int b;
int c;
int d;
};
class MyE{
public:
MyE() :abcd1(1, 2, 3, 4), abcd2(5, 6, 7, 8), m(10){
cout << endl;
cout << "MyE构造函数调用" << endl;
}
~MyE(){
cout << endl;
cout << "MyE构造函数调用" << endl;
}
MyE(const MyE&obj) :abcd1(11, 12, 13, 14), abcd2(15, 16, 17, 18), m(20){
cout << endl;
cout << "MyE拷贝构造函数调用" << endl;
}
int getM(){
return m;
}
private:
ABCD abcd1;
ABCD abcd2;
const int m;
};
void doThing(MyE mye1){
cout << endl;
cout << "doThing myE" << endl;
cout << mye1.getM() << endl;
}
int run01(){
printf("run() start\n");
MyE mye;
doThing(mye);//此时用实参赋值给形参，会调用myE类的拷贝构造函数
printf("run() end\n");
return 0;
}
int run02(){
//匿名对象或临时对象，因为没有对象去接它，因此当调用一次构造函数后，就会调用析构函数。
//ABCD(100, 200, 300, 400);临时对象的声明周期只存在于69行。
//如果匿名对象有对象去接，那么匿名对象就转正了，当return 0后才会调用析构函数。也不会调用拷贝构造函数，因为是转正不是赋值。
ABCD abcd = ABCD(100,200,300,400);
return 0;
}
int _tmain(int argc, _TCHAR* argv[])
{
int ret=run02();
return 0;
}