基类与派生类的构造函数

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转自http://www.quanxue.cn/JC_CLanguage/Cpp/Cpp08.html

一、缺省构造函数的调用关系

通过下面的例子，我们来看一下基类与派生的构造函数的调用顺序。创建时先基类后派生类。销毁时先派生类后基类。

#include <iostream>#include <string>using namespace std;class CBase {    string name;    int age;public:    CBase() {        cout << "BASE" << endl;    }    ~CBase() {        cout << "~BASE" << endl;    }};class CDerive : public CBase {public:    CDerive() {         cout << "DERIVE" << endl;    }    ~CDerive() {         cout << "~DERIVE" << endl;    }};int main ( ) {    CDerive d;    return 0;}

二、有参数时的传递

当有参数时，参数必须传送给基类。注意例子中传递的方法(第8行、第19行)。

#include <iostream>#include <string>using namespace std;class CBase {    string name;public:    CBase(string s) : name(s) {        cout << "BASE: " << name << endl;    }    ~CBase() {        cout << "~BASE" << endl;    }};class CDerive : public CBase {    int age;public:    CDerive(string s, int a) : CBase(s), age(a) {         cout << "DERIVE: " << age << endl;    }    ~CDerive() {         cout << "~DERIVE" << endl;    }};int main ( ) {    CDerive d("小雅", 27);    return 0;}

三、祖孙三代的参数传递

当有三层继承时，参数要一层一层地传递下去（第30行、第19行、第8行）。

#include <iostream>#include <string>using namespace std;class CBase {    string name;public:    CBase(string s) : name(s) {        cout << "BASE: " << name << endl;    }    ~CBase() {        cout << "~BASE" << endl;    }};class CDerive : public CBase {    int age;public:    CDerive(string s, int a) : CBase(s), age(a) {         cout << "DERIVE: " << age << endl;    }    ~CDerive() {         cout << "~DERIVE" << endl;    }};class CSon : public CDerive {    string id;public:    CSon(string s1, int a, string s2) : CDerive(s1, a), id(s2) {         cout << "SON: " << id << endl;    }    ~CSon() {         cout << "~SON" << endl;    }};int main ( ) {    CSon s("小雅", 27, "8503026");    return 0;}

四、多重继承的参数传递

多重继承时参数的传递方法和上面一样，要注意的是两个基类的顺序。决定2个基类的顺序是知27行。将27行的CBase1和CBase2的顺序交换一下，其结果中BASE1和BASE2的顺序也随之改变，与第30行无关。

#include <iostream>#include <string>using namespace std;class CBase1 {    string name;public:    CBase1(string s) : name(s) {        cout << "BASE1: " << name << endl;    }    ~CBase1() {        cout << "~BASE1" << endl;    }};class CBase2 {    int age;public:    CBase2(int a) : age(a) {        cout << "BASE2: " << age << endl;    }    ~CBase2() {        cout << "~BASE2" << endl;    }};class CDerive : public CBase1, public CBase2 {    string id;public:    CDerive(string s1, int a, string s2) : CBase1(s1), CBase2(a), id(s2) {         cout << "DERIVE: " << id << endl;    }    ~CDerive() {         cout << "~DERIVE" << endl;    }};int main ( ) {    CDerive d("小雅", 27, "8503026");    return 0;}

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