C++中的静态成员与this指针
一、静态成员
1、static 关键字
- 静态属性只能在全局范围内进行初始化赋值
- 静态方法可以直接通过类名进行访问，也可以通过对象名进行访问
class Teacher {
private:
char* name;
public:
//计数器
static int total;
public:
Teacher(char* name) {
this->name = name;
cout << "Teacher有参构造函数" << endl;
}
~Teacher() {
cout << "Teacher析构函数" << endl;
}
void setName(char* name) {
this->name = name;
}
char* getName() {
return this->name;
}
//计数的静态函数
static void count(){
total++;
cout << "total:" << total << endl;
}
};
//静态属性初始化赋值
int Teacher::total = 10;
void main() {
Teacher::total++;
cout << Teacher::total << endl;
//直接通过类名访问
Teacher::count();
cout << Teacher::total << endl;
//通过对象名访问
Teacher t1((char*)"JACK");
t1.count();
cout << Teacher::total << endl;
getchar();
}
二、类的大小
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
普通属性与结构体具有相同的内存布局
class A {
public:
int i;
int j;
int k;
};
class B {
public:
int i;
int j;
int k;
void myprint() {
cout << "打印" << endl;
}
};
void main() {
cout << sizeof(A) << endl;
cout << sizeof(B) << endl;
getchar();
}
三、this 指针
1、this指针
this 是当前对象的指针
因为函数是共享的，所有使用this指针用来标识当前对象
class Teacher {
private:
char* name;
int age;
public:
Teacher(char* name,int age) {
this->name = name;
this->age = age;
cout << "Teacher有参构造函数" << endl;
}
~Teacher() {
cout << "Teacher析构函数" << endl;
}
void setName(char* name) {
this->name = name;
}
char* getName() {
return this->name;
}
void setAge(int age) {
this->age = age;
}
int getAge() {
return this->age;
}
void myprint() {
cout << this->getName() << "," << this->getAge() << endl;
}
};
void main() {
Teacher t1((char*)"Jack", 20);
Teacher t2((char*)"Rose", 18);
t1.myprint();
t2.myprint();
getchar();
}
2、常函数（const修饰函数）
常函数，修饰的是this；既不能改变指针的值，也不能改变指针指向的内容
常量对象只能调用常量函数,不能调用非常量函数
常函数当前对象不能被修改，防止数据成员被非法访问
class Teacher {
private:
char* name;
int age;
public:
Teacher(char* name,int age) {
this->name = name;
this->age = age;
cout << "Teacher有参构造函数" << endl;
}
~Teacher() {
cout << "Teacher析构函数" << endl;
}
void setName(char* name) {
this->name = name;
}
char* getName() {
return this->name;
}
void setAge(int age) {
this->age = age;
}
int getAge() {
return this->age;
}
void myprint() const {
printf("%#x\n",this);
//不能改变属性的值
//this->name = "Jason";
//不能改变this指针的值
//this = (Teacher*)0x000090;
cout << this->getName() << "," << this->getAge() << endl;
}
};
四、友元函数与友元类
1、友元函数
在友元函数中可以访问私有的属性
class A {
private:
int i;
public:
A(int i) {
this->i = i;
}
void myprint() {
cout << i << endl;
}
//友元函数
friend void modify_i(A*p, int a);
};
//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->myprint();
modify_i(a, 20);
a->myprint();
getchar();
}
2、友元类
友元类可以访问引用友元类的类的任何成员
class A {
//友元类
friend class B;
private:
int i;
public:
A(int i) {
this->i = i;
}
void myprint() {
cout << i << endl;
}
//友元函数
friend void modify_i(A*p, int a);
};
//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;
}
class B {
private:
A a;
public:
B(int a_i):a(a_i) {
this->a = a;
}
//B这个友元类可以访问A类的任何成员
void accessAny() {
a.i = 30;
}
A getA() {
return a;
}
};
void main() {
B* b = new B(10);
A a = b->getA();
a.myprint();
b->accessAny();
a = b->getA();
a.myprint();
getchar();
}
五、运算符重载
运算符的重载，本质上还是函数的调用
1、单独进行运算符重载
class Point {
public:
int x;
int y;
public:
Point(int x = 0,int y = 0) {
this->x = x;
this->y = y;
}
void myprint() {
cout << x << "," << y << endl;
}
};
//重载+号
Point operator+(Point &p1, Point &p2) {
Point tmp(p1.x + p2.x, p1.y + p2.y);
return tmp;
}
//重载-号
Point operator-(Point &p1, Point &p2) {
Point tmp(p1.x - p2.x, p1.y - p2.y);
return tmp;
}
void main() {
Point p1(10,20);
Point p2(20,10);
Point p3 = p1 + p2;
p3.myprint();
getchar();
}
2、类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;
}
void myprint() {
cout << x << "," << y << endl;
}
//成员函数运算符重载+号
Point operator+(Point &p2) {
Point tmp(this->x + p2.x, this->y + p2.y);
return tmp;
}
//成员函数运算符重载-号
Point operator-(Point &p2) {
Point tmp(this->x - p2.x, this->y - p2.y);
return tmp;
}
};
void main() {
Point p1(10, 20);
Point p2(20, 10);
//p1.operator+(p1);
Point p3 = p1 + p2;
p3.myprint();
getchar();
}
3、友元函数运算符重载
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);
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 myprint() {
cout << x << "," << y << endl;
}
};
//友元函数运算符重载+号
Point operator+(Point &p1, Point &p2) {
Point tmp(p1.x + p2.x, p1.y + p2.y);
return tmp;
}
//友元函数运算符重载-号
Point operator-(Point &p1, Point &p2) {
Point tmp(p1.x - p2.x, p1.y - p2.y);
return tmp;
}
void main() {
Point p1(10, 20);
Point p2(20, 10);
Point p3 = p1 + p2;
p3.myprint();
getchar();
}
