asp教程.net的页面就是一个类，我们访问一个页面。就会在服务器上实例化一个该类的实例，来响应我们的请求。
在asp.net教程 C#中，static静态变量表示该变量属于静态的类，而不是类的实例。可以说是该类的所有实例共享一个static变量。
先来看一个测试实例
#include <iostream>
#include <iomanip>
using std::cout;
using std::endl;long next();
int main() {
for(int i = 0 ; i < 30 ; i++) {
cout << std::setw(12) << next ();
}
cout << endl;
return 0;
}long next () {
static long last = 0;
last = last + 1;
return last;
}输出结果
1 2 3 4 5 6
7 8 9 10 11 12 13
14 15 16 17 18 19 20
21 22 23 24 25 26
27 28 29 30
Application与static变量
Application是通过一个集合保存所有的对象。
强类型:
Application中保存的是object,对对象的保存和使用需要作cast动作。对于值类型更需要Box&UnBox。对性能的影响较大。
而static变量是强类型的对象。
线程同步:
Application将所有的对象放到一个集合，这样对访问集合中的任何对象都会锁定这个集合。
假如有Application["A"]、Application["B"]、Application["C"],有线程访问Application["A"]其他线程不能访问Application["B"] and Application["C"]。
而static变量，可以根据他们的作用分别放在不同的class当中。这样可以并行访问不同的static变量，而不存在线程安全问题。
使用静态变量来计算，平均运行的数字由用户输入
#include <iostream>
using namespace std;
int f(int i);
int main()
{
int num;
do {
cout << "Enter numbers (-1 to quit): ";
cin >> num;
if(num != -1)
cout << "average is: " << f(num) << "n";
} while(num > -1);
return 0;
}
int f(int i)
{
static int sum = 0, count = 0;
sum = sum + i;
count++;
return sum / count;
}结果是
Enter numbers (-1 to quit): 1
average is: 1
Enter numbers (-1 to quit): 2
average is: 1
Enter numbers (-1 to quit): 3
average is: 2
Enter numbers (-1 to quit): 2
average is: 2
Enter numbers (-1 to quit): 1
average is: 1
Enter numbers (-1 to quit): 2
average is: 1
Enter numbers (-1 to quit): 3
average is: 2
Enter numbers (-1 to quit): -1
在类外初始化静态成员字段声明
#include <iostream>
using std::cout;
using std::endl;class Box {
public:
Box() {
cout << "Default constructor called" << endl;
++objectCount;
length = width = height = 1.0;
}Box(double lvalue, double wvalue, double hvalue) :
length(lvalue), width(wvalue), height(hvalue) {
cout << "Box constructor called" << endl;
++objectCount;
}double volume() const {
return length * width * height;
}int getObjectCount() const {return objectCount;}
private:
static int objectCount;
double length;
double width;
double height;
};
int Box::objectCount = 0;int main() {
cout << endl;Box firstBox(17.0, 11.0, 5.0);
cout << "Object count is " << firstBox.getObjectCount() << endl;
Box boxes[5];
cout << "Object count is " << firstBox.getObjectCount() << endl;cout << "Volume of first box = "
<< firstBox.volume()
<< endl;const int count = sizeof boxes/sizeof boxes[0];
cout <<"The boxes array has " << count << " elements."
<< endl;cout <<"Each element occupies " << sizeof boxes[0] << " bytes."
<< endl;for(int i = 0 ; i < count ; i++)
cout << "Volume of boxes[" << i << "] = "
<< boxes[i].volume()
<< endl;return 0;
}结果为
Box constructor called
Object count is 1
Default constructor called
Default constructor called
Default constructor called
Default constructor called
Default constructor called
Object count is 6
Volume of first box = 935
The boxes array has 5 elements.
Each element occupies 24 bytes.
Volume of boxes[0] = 1
Volume of boxes[1] = 1
Volume of boxes[2] = 1
Volume of boxes[3] = 1
Volume of boxes[4] = 1
友情提示：
1. 对static变量，做lock时。可以通过lock(typeof(classname))来锁定该变量所在的类的类型，达到线程同步的目的。
2. 由于Aplication,static member是全局变量,而我们是在多线程服务器环境写程序，对他们的使用需要注意线程安全的问题