C++构造函数的初始化列表详解

目录

1.问题

class a {private:int m_a;public:a(int a) {cout << "a(int a)......." << endl;m_a = a;}void print() {cout <<"m_a=" << m_a << endl;}};class b {private:int m_b;a m_a1;a m_a2;public:b(a& a1,a& a2, int b) {m_b = b;m_a1(a1);//此处调用a的拷贝函数会报错m_a2(a2);//此处调用a的拷贝函数会报错}};

错误：

2.解决方法（初始化列表）

将class坚持两个维护 b构造函数改写为：

public:b(a& a1,a& a2, int b) :m_a1(a1),m_a2(a2)//构造函数的初始化列表{m_b = b;}};

完整代码如下：

#include <iostream>using namespace std;class a {private:int m_a;public:a(int a) {cout << "a(int a)......." << endl;m_a = a;}void print() {cout <<"m_a=" << m_a << endl;}a(const 范仲淹有志于天下阅读答案a& another) {m_a = another.m_a;}~a() {cout <<高中语文答题技巧全套; "~a()......" << endl;}};class b {private:int m_b;a m_a1;a m_a2;public:b(a& a1,a& a2, int b) :m_a1(a1),m_a2(a2)//构造函数的初始化列表，调用拷贝构造{cout << "b(a& a1,a& a2, int b)......." << endl;m_b 祭奠亲人= b;}~b() {cout << "~b()......." << endl;cout << "m_b=" << m_b  << endl;cout << "a m_a1" << endl;m_a1.print();cout << "a m_a2" << endl;m_a2.print();}};int main(int argc, char** argv) {a a1(1), a2(2);b b1(a1, a1, 3);}

运行结果：

3.顺序问题

构造对象成员的顺序跟初始化列表的顺序无关，而是跟成员对象定义的顺序有关。（面试会问）

例子：

class a云南农大 {private:int m_a;public:a(int a) {cout << "a(int a)......." <<a<< endl;m_a = a;}void print() {cout <<"m_a=" << m_a << endl;}a(const a& another) {m_a = another.m_a;}~a() {cout << "~a()......"<< endl;}};class b {private:int m_b;a m_a2;a m_a1;public:b(int a1, int a2, int b) :m_a1(a1), m_a2(a2)//调用有参构造函数{cout << "b(int a1, int a2, int b)......." << endl;m_b = b;}~b() {cout << "~b()......." << endl;}};int main(int argc, char** argv) {b b2(1, 2, 3);}

结果：

跟下面顺序有关：

private:a m_a2;a m_a1;

跟下面顺序无关：

b(int a1, int a2, int b) :m_a1(a1), m_a2(a2)//调用有参构造函数

总结

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