QtProject02

C++类中的静态成员

#include <iostream>
using namespace std;
class Box
{
   public:
      static int objectCount;
      // 构造函数定义
      Box(double l=2.0, double b=2.0, double h=2.0)
      {
         cout <<"Constructor called." << endl;
         length = l;
         breadth = b;
         height = h;
         // 每次创建对象时增加 1
         objectCount++;
      }
      double Volume()
      {
         return length * breadth * height;
      }
   private:
      double length;     // 长度
      double breadth;    // 宽度
      double height;     // 高度
};
// 初始化类 Box 的静态成员
int Box::objectCount = 0;
int main(void)
{
   Box Box1(3.3, 1.2, 1.5);    // 声明 box1
   Box Box2(8.5, 6.0, 2.0);    // 声明 box2
   // 输出对象的总数
   cout << "Total objects: " << Box::objectCount << endl;
   return 0;
}

C++中的静态成员函数，保证静态成员不被外部更改

#include <stdio.h>
class Test
{
private:
    static int cCount;
public:
    Test()
    {
        cCount++;
    }
    ~Test()
    {
        --cCount;
    }
    static int GetCount()
    {
        return cCount;
    }
};
int Test::cCount = 0;
int main()
{
    printf("count = %d\n", Test::GetCount());
    Test t1;
    Test t2;
    printf("count = %d\n", t1.GetCount());
    printf("count = %d\n", t2.GetCount());
    Test* pt = new Test();
    printf("count = %d\n", pt->GetCount());
    delete pt;
    printf("count = %d\n", Test::GetCount());
    return 0;
}
结果 
count = 0
count = 2
count = 2
count = 3
count = 2

C++中const修饰静态成员

#include <iostream>
#include <stdio.h>
class Test
{
private:
    const static int cCount;
public:
    static int GetCount()
    {
        return cCount;
    }
};
const int Test::cCount = 100;
int main()
{
    printf("count = %d\n", Test::GetCount());
    return 0;
}