深度探索c++学习笔记

D d1 = d; 这个是调用的是复制构造函数

函数参数是以copy constructor初始化的

Default constructor的错误认为:(P47)

任何class如果没有定义default constructor,就会被合成一个出来,其实不是.(要有四种之一,带有default constructor的member class object或base class或带有一个virtual function的class或者带有一个virtual base class 的class)

编译器合成出来的default constructor会现实定义”class内每一个data member的默认值”,其实不是.(一些内置类型是不会的)

Default copy也是有上述四种情况才会自动生成的

带有default constructor的member class object

class B{

public:

B(){

cout << "B" << endl;

}

};

class D{

public:

D(){

}

private:

int c;

B b;

};

带有default constructor的base class

int main(){

D d; 输入B,编译器会自动添加B的初始化(在D构造函数中加),但是会初始话c

cout << d.c;

return 0;

}

class B{ 与上面的返回值一样

public:

B(){

cout << "B" << endl;

}

};

class D: public B{

public:

D(){

}

int c;

};

int main(){

D d;

cout << d.c;

return 0;

}

enum n{N,M,K,J,L};

cout << sizeof(n) << endl; //输出4

class B{

public:

virtual void x(){

cout << "call B virtual x()" << endl;

}

};

class D: public B{

public:

void x(){

cout << "call D virtual x()" << endl;

}

};

int main(){

B *b = new D;

(*b).x();

返回的还是D类中的x();

在下列情况下你必须使用member initialization list:

当初始化一个reference member时;

当初始化一个const member时;

当调用一个base class的constructor,而它拥有一组参数时

当调用一个member class的constructor,而它拥有一组参数时

class X{

};

class Y: virtual public X{};

class Z: virtual public X{};

class T: public Y, public Z{};

int main(){

cout << "X: " << sizeof(X) << endl; //1

cout << "Y: " << sizeof(Y) << endl; //4

cout << "Z: " << sizeof(Z) << endl; //4

cout << "T: " << sizeof(T) << endl; //8

X x;

Y y;

Z z;

T t;

cout << "x: " << sizeof(x) << endl;

cout << "y: " << sizeof(y) << endl;

cout << "z: " << sizeof(z) << endl;

cout << "t: " << sizeof(t) << endl;

return 0;

}

class X{

};

class Y: virtual public X{};

class Z: virtual public X{};

class T: public Y, virtual public Z{};

int main(){

cout << "X: " << sizeof(X) << endl; //1

cout << "Y: " << sizeof(Y) << endl; //4

cout << "Z: " << sizeof(Z) << endl; //4

cout << "T: " << sizeof(T) << endl; //8

X x;

Y y;

Z z;

T t;

cout << "x: " << sizeof(x) << endl;

cout << "y: " << sizeof(y) << endl;

cout << "z: " << sizeof(z) << endl;

cout << "t: " << sizeof(t) << endl;

return 0;

}

class X{

};

class Y: virtual public X{};

class Z: virtual public X{};

class T: virtual public Y, virtual public Z{};

int main(){

cout << "X: " << sizeof(X) << endl; //1

cout << "Y: " << sizeof(Y) << endl; //4

cout << "Z: " << sizeof(Z) << endl; //4

cout << "T: " << sizeof(T) << endl; //12

X x;

Y y;

Z z;

T t;

cout << "x: " << sizeof(x) << endl;

cout << "y: " << sizeof(y) << endl;

cout << "z: " << sizeof(z) << endl;

cout << "t: " << sizeof(t) << endl;

return 0;

}

Data Member绑定

typedef int length;

class X{

public:

void mumble(length val){ _val = 1.1;} //这里的length是global的

length mumble(){return _val;} //这里的length也是global的

public:

typedef float length;

length _val; //class的

};

int main(){

X x;

x.mumble(1.1);

cout << x.mumble() << endl; //1

cout << x._val << endl; //1.1

return 0;

}

如果想要typedef int length是class内的就要在类的开始定义就好,但是类内成员变量就不会有这问题

class X{

public:

static int l;

float x;

};

class Y : public X{

};

int X::l = 10;

int main(){

cout << X::l << endl; //10

cout << Y::l << endl; //10

X::l = 11;

cout << Y::l << endl; //11 因为X,Y是共享存储在data segment的l

return 0;

}

P103

class X{

private:

int l;

char a;

char b;

};

int main(){

cout << "sizeof(X):" << sizeof(X) << endl; //8

return 0;

}

class X{

public:

int l;

char a;

};

class Y: public X{

public:

char b;

};

int main(){

cout << "sizeof(Y):" << sizeof(Y) << endl; //12 原因X的补充不会与Y相连

return 0; 想想X x; Y y; x = y,如果是相连的话会使x中有个未知的b成员变量在最后

}

class B{

public:

virtual void func();

};

class D: virtual public B{

public:

virtual void fun();

};

int main(){

cout << "sizeof(B):" << sizeof(B) << endl; //4

cout << "sizeof(D):" << sizeof(D) << endl; //12自己也有一个虚table指针,一个指向

return 0; B的指针,还有就是B父类的大小

}

class B{

public:

virtual void func();

};

class D: virtual public B{

};

int main(){

cout << "sizeof(B):" << sizeof(B) << endl; //4

cout << "sizeof(D):" << sizeof(D) << endl; //8 一个指向B的指针,还有就是B的大小

return 0;

}

class B{

public:

virtual void func();

};

class D: public B{

public:

virtual void fun();

};

int main(){

cout << "sizeof(B):" << sizeof(B) << endl; //4

cout << "sizeof(D):" << sizeof(D) << endl; //4 只有一个虚table指针

return 0;

}

class B{

public:

static void func() const; //错误,const 函数不能是static因为const指代

}; 对象中的成员变量不能改变,但是static是类层次的

编译器会将member function 转换成为一个独一无二的nonmember function

class B{

public:

virtual B* func() const;

};

class D: virtual public B{

public:

virtual D* func() const; //虽然D*返回的类型与B*不一样,但是有继承

}; 关系,所以这个虚拟继承是符合的

class B1{

public:

virtual B1* func() const{}

};

class B2{

public:

virtual B2* func() const{}

};

class D: public B1, public B2{

};

int main(){

cout << "sizeof(B1):" << sizeof(B1) << endl; //4

cout << "sizeof(D):" << sizeof(D) << endl; //8因为D会有两个vptr,分别指向两个子类

return 0;

}

单一继承:



多重继承:



虚拟继承: