Question

首先，我使用VS2008（不支持C ++ 11）。我无法升级并且只需要使用本机库，因为它需要在另一个人身上编译。我无法控制的编译器。

我想在5秒后自动运行代码，而不必轮询已经过了多少秒。

这是我的不完整代码

#include <windows.h>
#include <iostream>
void runMeAfterFiveSeconds(){
     cout<<"I'm activated!"<<endl;
}
void main(){
     while(1){
          cout<<"hello there!"<<endl;
          Sleep(2000);
     }
}

示例输出

hello there!
hello there! //after 2 seconds
hello there! //after 4 seconds
I'm activated! //after 5 seconds
hello there! //after 6 seconds
hello there! //after 8 seconds
hello there! //after 10 seconds
I'm activated! //after 10 seconds
...

Answer 1

此示例显示了如何使用非常简单的调度算法来完成此操作。不需要产生额外的线程。

#include <stdio.h>
#include <windows.h>

int main(int argc, char ** argv)
{
   DWORD now                      = timeGetTime();
   DWORD nextPrintHelloThereTime  = now;
   DWORD nextPrintImActivatedTime = now+5000;

   while(1)
   {
      now = timeGetTime();
      DWORD nextEventTime = (nextPrintHelloThereTime < nextPrintImActivatedTime) ? nextPrintHelloThereTime : nextPrintImActivatedTime;

      DWORD millisecondsToSleep = nextEventTime-now;
      Sleep(millisecondsToSleep);

      now = timeGetTime();
      if (now >= nextPrintHelloThereTime)
      {
         printf("hello there!\n");
         nextPrintHelloThereTime += 2000;
      }
      if (now >= nextPrintImActivatedTime)
      {
         printf("I'm activated!\n");
         nextPrintImActivatedTime += 5000;
      }
   }
}

Answer 2

这实际上取决于您要执行的代码以及您希望如何执行它。这样做的非常简单的方法是创建一个单独的线程并在其中Sleep()。因此，由于您无法从Visual Studio 2008升级（如果我没记错，不支持C ++ 11），您必须使用本机Windows线程或某些库实现（如Boost.Thread）。要查找如何使用Windows线程，请参阅MSDN documentation on _beginthreadex() function。可以看到关于Boost.Thread的简短教程here。

两者的快速示例，直接取自我提供的链接：

1）Windows线程：

// crt_begthrdex.cpp
// compile with: /MT
#include <windows.h>
#include <stdio.h>
#include <process.h>

unsigned Counter; 
unsigned __stdcall SecondThreadFunc( void* pArguments )
{
    printf( "In second thread...\n" );

    while ( Counter < 1000000 )
        Counter++;

    _endthreadex( 0 );
    return 0;
} 

int main()
{ 
    HANDLE hThread;
    unsigned threadID;

    printf( "Creating second thread...\n" );

    // Create the second thread.
    hThread = (HANDLE)_beginthreadex( NULL, 0, &SecondThreadFunc, NULL, 0, &threadID );

    // Wait until second thread terminates. If you comment out the line
    // below, Counter will not be correct because the thread has not
    // terminated, and Counter most likely has not been incremented to
    // 1000000 yet.
    WaitForSingleObject( hThread, INFINITE );
    printf( "Counter should be 1000000; it is-> %d\n", Counter );
    // Destroy the thread object.
    CloseHandle( hThread );
}

2）Boost.Thread：

struct callable
{
    void operator()();
};

boost::thread copies_are_safe()
{
    callable x;
    return boost::thread(x);
} // x is destroyed, but the newly-created thread has a copy, so this is OK

在第二个示例中，您也可以使用普通函数指针作为boost::thread构造函数参数。此外，您可以使用指向多个参数的指针 - 豪华Windows API的线程不提供。

Answer 3

您可能只需要创建一个类似的线程：

#include <windows.h>
#include <iostream>
#include <thread>
void runMeAfterFiveSeconds(){
     while(true){
          sleep(5000);
          cout<<"I'm activated!"<<endl;   
     }     
}
void main(){
     std::thread th(runMeAfterFiveSeconds);
     while(1){
          cout<<"hello there!"<<endl;
          Sleep(2000);
     }
}

Answer 4

你必须要么做一个主题（编码橙色答案，可能是更好的方法），或者只是全力以赴。

void runMeAfterFiveSeconds(){
     cout << "I'm activated!" <<endl;        
}

void main(){
     while(1){
          cout << "hello there!" << endl;
          Sleep(2000);
          cout << "hello there!" << endl;
          Sleep(3000);
          runMeAfterFiveSeconds();
          Sleep(1000);
          cout << "hello there!" << endl;
          Sleep(2000);
          cout << "hello there!" << endl;
          Sleep(2000);
          cout << "hello there!" << endl;
          runMeAfterFiveSeconds();
     }
}

C ++：如何在几秒钟后执行一个函数？

4 个答案: