C++之深入讨论构造函数

1、深拷贝与浅拷贝浅拷贝：默认拷贝构造函数，系统提供深拷贝：手动定义拷贝构造函数，具体复制动作由自己完成（涉及地址时必须用）2、拷贝构造函数的使用拷贝构造函数与普通构造函数的唯一不同点在于参数不同DEMO类的拷贝构造函数为：DEMO（const DEMO &a）;3、特殊情况：const类成员中若有const修饰，必须在对象初始化时给const int m 赋值 ：Student类中Student::Student（）：m（v1）类的成员函数中有const修饰，同上。

#include <iostream>
#include <cstring>

using namespace std;

class Stu
{
private:
int m_bir;
char m_name[20];
int m_num;
int m_cla;
public:
Stu(int b,char *name);
void show();
};

Stu::Stu(int b,char *name):m_bir(b),m_num(15),m_cla(2)
{
strcpy(m_name,name);
}

void Stu::show()
{
cout << "name : " << m_name << "  birthday : " << m_bir << endl;
cout << "number : " << m_num << "  class : " << m_cla << endl;
}

int main()
{
Stu a(123,"wenwanwan");
a.show();
return 0;
}

#include <iostream>
using namespace std;
class Test
{
private:const int m_a;
public:Test(int a);
int GetA() const;
};
Test::Test(int a):m_a(a)
{
//m_a = a;
}
int Test::GetA() const
{
return m_a;
}
int main()
{
Test t(1);
cout << t.GetA() << endl;
return 0;
}

4、成员变量的初始化顺序与声明的顺序相关，与在初始化列表中的顺序无关 5、析构函数调用顺序与构造函数顺序相反

#include <iostream>#include <cstring>using namespace std;class Test{private:int m;public:Test(int n);~Test();};Test::Test(int n){cout << "Test Constructor !" << endl;m = n;}Test::~Test(){cout << "Test Destruct !" << endl;}class Bir{private:int year;int mouth;int day;public:Bir(int _year,int _mouth,int _day);void print();~Bir();};class Stu{private:Test t;//此处调用不同类的顺序决定对应类构造函数调用的顺序Bir m_bir;//若34，35互换，则调用顺序变化char m_name[20];int m_num;int m_cla;public:// Stu(char *name);Stu(int year,int mouth,int day,char *name);void show();~Stu();};Bir::Bir(int _year,int _mouth,int _day){cout << "Birthday constructor !" << endl;year = _year;mouth = _mouth;day = _day;}void Bir::print(){cout << "year : " << year << " mouth : " << mouth << " day : " << day << endl;}Bir::~Bir(){cout << "Birthday Destruct !" << endl;}//Stu::Stu(char *name):m_num(15),m_cla(2),m_bir(1997,5,27)Stu::Stu(int year,int mouth,int day,char *name):m_num(15),m_cla(2),m_bir(year,mouth,day),t(2)//此处初始化列表顺序与成员变量顺序无关{cout << "Sturdent Constructor !" << endl;strcpy(m_name,name);}void Stu::show(){cout << "name : " << m_name << endl;m_bir.print();cout << "number : " << m_num << "  class : " << m_cla << endl;}Stu::~Stu(){cout << "Student Destruct !" << endl;}//析构函数与对应的构造函数的调用顺序相反int main(){//Stu a("wenwanwan");Stu a(1997,5,27,"wenwanwan");a.show();return 0;}

运行结果：Test Constructor !Birthday constructor !Sturdent Constructor !name : wenwanwanyear : 1997 mouth : 5 day : 27number : 15 class : 2Student Destruct !Birthday Destruct !Test Destruct !6、匿名对象匿名对象生命周期短，调用完构造函数后，立即调用析构函数，只存在匿名对象所在行有效注意：手动调用构造函数时，会产生一个匿名对象，构造中调用构造是危险行为！

#include <iostream>using namespace std;class Test{private:int m_a;public:Test(int a);~Test();};Test::Test(int a){cout << "Test Constructor !" << endl;m_a = a;}Test::~Test(){cout << "Test Destruct !" << endl;}int main(){Test(2);//匿名对象，生命周期只存在此行，调用构造函数后立即调用析构函数Test a(1);//有名对象，对象结束后调用析构函数Test b(3);return 0;}运行结果：Test Constructor !Test Destruct !Test Constructor !Test Constructor !Test Destruct !Test Destruct !#include <iostream>using namespace std;class Test{private:int m_a;int m_b;int m_c;public:Test(int a,int b,int c);Test(int a,int b);int Getc();~Test();};Test::Test(int a,int b,int c){cout << "Test Constructor_3 !" << endl;m_a = a;m_b = b;m_c = c;}Test::Test(int a,int b){cout << "Test Constructor_2 !" << endl;m_a = a; m_b = b;Test(a,b,3);//在构造函数中调用构造函数是危险行为，会产生一个新的匿名对象//即用即释放，故c为垃圾值}int Test::Getc(){cout << "c = " << m_c << endl;}Test::~Test(){cout << "Test Destruct !" << endl;}int main(){Test t(1,2);t.Getc();return 0;}运行结果：Test Constructor_2 !Test Constructor_3 !Test Destruct !c = 13963252Test Destruct !