Android NDK基础20:C++_类大小_友元函数_运算符重载

类大小

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//类的大小
class A {
public:
int i;
int j;
int k;
static int m;
};

class B {
public:
int i;
int j;
int k;

void printf() {
cout << "打印" << endl;
}
};

void main() {
cout << sizeof(A) << endl; //12
cout << sizeof(B) << endl; //12

//C/C++ 内存分区:栈、堆、全局(静态、全局)、常量区(字符串)、程序代码区
//普通属性与结构体相同的内存布局

//JVM 内存分区:
//JVM Stack(基本数据类型、对象引用)
//Native Method Stack(本地方法栈)
//方法区

system("pause");
}

友元函数

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//友元函数
class A {
//友元函数
friend void modify_i(A *p, int a);
private:
int i;
public:
A(int i) {
this->i = i;
}

void print() {
cout << i << endl;
}
};

//友元函数的实现,在友元函数中可以访问私有的属性
void modify_i(A *p, int a) {
p->i = a;
}

void main() {
A* a = new A(10);
a->print();

modify_i(a, 20);
a->print();

system("pause");
}
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//友元类
class A {
//友元类
friend class B;
private:
int i;
public:
A(int i) {
this->i = i;
}

void print() {
cout << i << endl;
}
};

class B {
public:
//B这个友元类可以访问A类的任何成员
void accessAny() {
a.i = 30;
}
private:
A a;
};

运算符重载

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//运算符重载
class Point {
public:
int x;
int y;
public:
Point(int x = 0, int y = 0) {
this->x = x;
this->y = y;
}

void print() {
cout << x << "," << y << endl;
}
};

//重载+号
Point operator+(Point &p1, Point &p2) {
Point p(p1.x + p2.x, p1.y + p2.y);
return p;
}

//重载-号
Point operator-(Point &p1, Point &p2) {
Point p(p1.x - p2.x, p1.y - p2.y);
return p;
}

void main() {
Point p1(10, 20);
Point p2(20, 10);

Point p3 = p1 + p2;

p3.print();

system("pause");
}
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//成员函数,运算符重载
class Point {
public:
int x;
int y;
public:
Point(int x = 0, int y = 0) {
this->x = x;
this->y = y;
}

//成员函数,运算符重载
Point operator+(Point &p2) {
Point tmp(this->x + p2.x, this->y + p2.y);
return tmp;
}

void print() {
cout << x << "," << y << endl;
}
};

void main() {
Point p1(10, 20);
Point p2(20, 10);

//运算符的重载,本质还是函数调用
//p1.operator+(p2)
Point p3 = p1 + p2;

p3.print();

system("pause");
}
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//当属性私有时,通过友元函数完成运算符重载
class Point {
friend Point operator+(Point &p1, Point &p2);
private:
int x;
int y;
public:
Point(int x = 0, int y = 0) {
this->x = x;
this->y = y;
}

void print() {
cout << x << "," << y << endl;
}
};

Point operator+(Point &p1, Point &p2) {
Point p(p1.x + p2.x, p1.y + p2.y);
return p;
}

void main() {
Point p1(10, 20);
Point p2(20, 10);

//运算符的重载,本质还是函数调用
//p1.operator+(p2)
Point p3 = p1 + p2;

p3.print();

system("pause");
}

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