C++ : How do I execute a function after several seconds? - c++

Question

Firstly, I'm using VS2008 (doesn't support C++11). I can't upgrade and need to use native libraries only because it needs to be compiled on another persons' compiler which I don't have control over.
I would like to run the code automatically after 5 seconds without having to poll how many seconds have elapsed.
This is my incomplete code
#include <windows.h>
#include <iostream>
void runMeAfterFiveSeconds(){
cout<<"I'm activated!"<<endl;
}
void main(){
while(1){
cout<<"hello there!"<<endl;
Sleep(2000);
}
}
Example output
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

This example shows how to do it using a very simple scheduling algorithm. No spawning of additional threads is required.
#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

It really depends on what code you want to execute and how you want it to be executed.
The very simple way of doing so would be creating a separate thread and Sleep() in it.
So, since you cannot upgrade from Visual Studio 2008 (which, if I remember correctly, does not support C++11), you have to use either native Windows threads or some library implementation like Boost.Thread.
To look up how to use Windows threads, see MSDN documentation on _beginthreadex() function.
A short tutorial about Boost.Thread can bee seen here.
Quick examples of both, taken directly from the links I provided:
1) Windows threads:
// 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
In the second example, you could as well have used a plain function pointer as boost::thread constructor argument. Moreover, you could use a pointer to function with multiple arguments - a luxury Windows API's threads do not provide.

Answer 3

You're probably just going to need to create a thread like so:
#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

You're going to have to either make a thread (Coding Orange's answer, probably the better way), or just write it all out.
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();
}
}