前置++和后置++的区别

今天看了一下windows c中多线程编程，写了一小段程序。死活跑出结果，先贴一下我的代码

 1 #include <windows.h>
 2 #include <iostream.h>
 3 #include <string>
 4
 5 using namespace std;
 6
 7 DWORD WINAPI countThread1(LPVOID argv);//声明一个线程函数
 8 DWORD WINAPI countThread2(LPVOID argv);
 9
10 int main(){
11     //创建两个线程
14     HANDLE handle1 = CreateThread(NULL, 0, countThread1, NULL, 0, NULL);
16
17     WaitForSingleObject(handle1, INFINITE);
24
25
26     return 0;
27 }
28 //下面是两个线程函数
29 DWORD WINAPI countThread1(LPVOID argv){
30     int i = 0;
31     cout<<"i am in"<<endl;
32     while(i++){　　　　　　//这里开始没看出来有错，开始没注意这段代码，以为是main里面出错了。后面输出i am in我知道这段代码有问题了
33         if(10 == i)
34             ExitThread(0);
35         cout<<"this is thread2 and i = "<<i<<endl;
36         Sleep(1000);
37     }
38
39     return 0;
40 }
41 DWORD WINAPI countThread2(LPVOID argv){
42     int i = 0;
43     while(i++){
44         if(10 == i)
45             ExitThread(0);
46         cout<<"this is thread2 and i = "<<i<<endl;
47         Sleep(1000);
48     }
49     return 0;
50 }

while循环中，因为i = 0为初始条件，后置的i ++会先判断条件，i = 0不会执行while语句。将i++变成++i就好了

 1 #include <windows.h>
 2 #include <iostream.h>
 3 #include <string>
 4
 5 using namespace std;
 6
 7 DWORD WINAPI countThread1(LPVOID argv);//声明一个线程函数
 8 DWORD WINAPI countThread2(LPVOID argv);
 9
10 int main(){
11     //创建两个线程
12 //    int i = 0;
13 //    while(i < 50){
14     HANDLE handle1 = CreateThread(NULL, 0, countThread1, NULL, 0, NULL);
15 //    HANDLE handle2 = CreateThread(NULL, 0, countThread2, NULL, 0, NULL);
16
17     WaitForSingleObject(handle1, INFINITE);
18 //    WaitForSingleObject(handle2, INFINITE);
19
20             //CreateThread(NULL, 0, countThread2, NULL, 0, NULL);
21             //Sleep(50000);
22
23 //    }
24
25
26     return 0;
27 }
28 //下面是两个线程函数
29 DWORD WINAPI countThread1(LPVOID argv){
30     int i = 0;
31     cout<<"i am in"<<endl;
32     while(++i){
33         if(10 == i)
34             ExitThread(0);
35         cout<<"this is thread2 and i = "<<i<<endl;
36         Sleep(1000);
37     }
38
39     return 0;
40 }
41 DWORD WINAPI countThread2(LPVOID argv){
42     int i = 0;
43     while(++i){
44         if(10 == i)
45             ExitThread(0);
46         cout<<"this is thread2 and i = "<<i<<endl;
47         Sleep(1000);
48     }
49     return 0;
50 }

这里就会每秒输出，一条信息

ps:

WaitForSingleObject(handle1, INFINITE);现在要加上这条语句才可以。