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Timing in C++

Frank14 (93)
Hi all,

In section 26.6.1 (Timing) Stroustrup in its book (Programming Principles And Practice Using C++ 2nd Edition May 2014) declare this code:

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#include <iostream>
#include <chrono>
using namespace std;

int main()
{
	int n = 1000000;
	auto t1 = system_clock::now();
	for (int i = 0; i < n; i++)
		i += i;

	auto t2 = system_clock::now();

	cout << "The loop " << n << " times too "
		<< dynamic_cast<milliseconds>(t2 - t1).count() << " milliseconds\n";

   system("pause");
   return 0;
}


When I run it on VS 2017 I get many errors including:

Severity Code Description Project File Line Suppression State
Error C2653 'system_clock': is not a class or namespace name

Severity Code Description Project File Line Suppression State
Error C3861 'now': identifier not found

What is the problem please? It's odd to see a code with these many errors in that book.



Last edited on
closed account (48T7M4Gy)
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#include <iostream>
#include <chrono>
using namespace std;

int main()
{
	int n = 1000000;
	auto t1 = std::chrono::system_clock::now();
	for (int i = 0; i < n; i++)
		i += i;

	auto t2 = std::chrono::system_clock::now();

	cout 
	<< "The loop " << n << " times too "
	<< std::chrono::duration_cast<std::chrono::nanoseconds>(t2 - t1).count() << " nanoseconds\n";

   system("pause");
   return 0;
}
closed account (48T7M4Gy)
Also, you can leave out std:: everywhere because you have adopted the un-preferred using namespace std;
Frank14 (93)
Thank you, it worked.
I'm rather astonished why he has written the code that way.
Duthomhas (13119)
The code is older than the book.
closed account (48T7M4Gy)
My guess is it's #included in a Stroustrups facilities-library-type file. Details are probably somewhere in his fine print or on a web page. Who knows?
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