static menmbers of a c++ class
当我们声明一个类成员为static的时候，这意味着无论有其他多少种类的对象被创建了，也仅有这一份静态成员的copy。
静态成员也被类的所有对象共享。
Live Demo
#include <iostream>
using namespace std;
class Box {
public:
static int objectCount;
// Constructor definition
Box(double l = 2.0, double b = 2.0, double h = 2.0) {
cout <<"Constructor called." << endl;
length = l;
breadth = b;
height = h;
// Increase every time object is created
objectCount++;
}
double Volume() {
return length * breadth * height;
}
private:
double length; // Length of a box
double breadth; // Breadth of a box
double height; // Height of a box
};
// Initialize static member of class Box
int Box::objectCount = 0;
int main(void) {
Box Box1(3.3, 1.2, 1.5); // Declare box1
Box Box2(8.5, 6.0, 2.0); // Declare box2
// Print total number of objects.
cout << "Total objects: " << Box::objectCount << endl;
return 0;
}
结果
Constructor called.
Constructor called.
Total objects: 2
static function members
声明一个静态成员函数，这将会让它独立于类的所有对象。
静态成员函数只能访问静态数据成员，其他静态成员函数和类外所有函数。
Static member functions have a class scope and they do not have access to the this pointer of the class. You could use a static member function to determine whether some objects of the class have been created or not.
#include <iostream>
using namespace std;
class Box {
public:
static int objectCount;
// Constructor definition
Box(double l = 2.0, double b = 2.0, double h = 2.0) {
cout <<"Constructor called." << endl;
length = l;
breadth = b;
height = h;
// Increase every time object is created
objectCount++;
}
double Volume() {
return length * breadth * height;
}
static int getCount() {
return objectCount;
}
private:
double length; // Length of a box
double breadth; // Breadth of a box
double height; // Height of a box
};
// Initialize static member of class Box
int Box::objectCount = 0;
int main(void) {
// Print total number of objects before creating object.
cout << "Inital Stage Count: " << Box::getCount() << endl;
Box Box1(3.3, 1.2, 1.5); // Declare box1
Box Box2(8.5, 6.0, 2.0); // Declare box2
// Print total number of objects after creating object.
cout << "Final Stage Count: " << Box::getCount() << endl;
return 0;
}
结果
Inital Stage Count: 0
Constructor called.
Constructor called.
Final Stage Count: 2
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