Working with timers - c++

Question

I am trying to create a timer where it begins with a certain value and ends with another value like.
int pktctr = (unsigned char)unpkt[0];
if(pktctr == 2)
{
cout << "timer-begin" << endl;
//start timer here
}
if(pktctr == 255)
{
cout << "timer-end" << endl;
//stop timer here
//timer display total time then reset.
}
cout << "displays total time it took from 1 to 255 here" << endl;
Any idea on how to achieve this?
void WINAPI MyUCPackets(char* unpkt, int packetlen, int iR, int arg)
{
int pktctr = (unsigned char)unpkt[0];
if(pktctr == 2)
{
cout << "timer-begin" << endl;
}
if(pktctr == 255)
{
cout << "timer-end" << endl;
}
return MyUC2Packets(unpkt,packetlen,iR,arg);
}
Everytime this function is called unpkt starts from 2 then reaches max of 255 then goes back to 1. And I want to compute how long it took for every revolution?
This will happen alot of times. But I just wanted to check how many seconds it took for this to happen because it won't be the same everytime.
Note: This is done with MSDetours 3.0...

Answer 1

I'll assume you're using Windows (from the WINAPI in the code) in which case you can use GetTickCount:
/* or you could have this elsewhere, e.g. as a class member or
* in global scope (yuck!) As it stands, this isn't thread safe!
*/
static DWORD dwStartTicks = 0;
int pktctr = (unsigned char)unpkt[0];
if(pktctr == 2)
{
cout << "timer-begin" << endl;
dwStartTicks = GetTickCount();
}
if(pktctr == 255)
{
cout << "timer-end" << endl;
DWORD dwDuration = GetTickCount() - dwStartTicks;
/* use dwDuration - it's in milliseconds, so divide by 1000 to get
* seconds if you so desire.
*/
}
Things to watch out for: overflow of GetTickCount is possible (it resets to 0 approximately every 47 days, so it's possible that if you start your timer close to the rollover time, it will finish after the rollover). You can solve this in two ways, either use GetTickCount64 or simply notice when dwStartTicks > GetTickCount and if so, calculate how many milliseconds were from dwStartTicks until the rollover, and how many millseconds from 0 to the result of GetTickCount() and add those numbers together (bonus points if you can do this in a more clever way).
Alternatively, you can use the clock function. You can find out more on that, including an example of how to use it at http://msdn.microsoft.com/en-us/library/4e2ess30(v=vs.71).aspx and it should be fairly easy to adapt and integrate into your code.
Finally, if you're interested in a more "standard" solution, you can use the <chrono> stuff from the C++ standard library. Check out http://en.cppreference.com/w/cpp/chrono for an example.

Answer 2

If you want to use the Windows-API use GetSystemTime(). Provide a struct SYSTEMTIME, initialize it properly and pass it to GetSystemTime():
#include <Windows.h>
...
SYSTEMTIME sysTime;
GetFileTime(&sysTime);
// use sysTime and create differences
Look here for GetSystemTime() there is a link for SYSTEMTIME there, too.

Answer 3

I think boost timer is the best solution for you.
You can check the elapsed time like this:
#include <boost/timer.hpp>
int main() {
boost::timer t; // start timing
...
double elapsed_time = t.elapsed();
...
}