Re: elapsed time 0 with std::cin

"Jim Langston" <>
Sun, 25 Nov 2007 01:23:45 -0800
"James Kanze" <> wrote in message
On Nov 23, 9:43 pm, "Jim Langston" <> wrote:

"pekka" <pe...@nospam.invalid> wrote in message


Here's my code:

#include <ctime>
#include <iostream>
#include <string>

class Timer
clock_t start_, nticks_;

Timer() : nticks_(0) { start(); }
~Timer() {}

void start() { start_ = clock(); }
void stop() { nticks_ = clock() - start_; }
double elapsed() const { return double(nticks_) / CLOCKS_PER_SEC; }

int main()
std::string answer;
Timer T;
// for (int n=0; n<100000000; ++n);
std::cout << "? ";
std::cin >> answer;
std::cout << "time elapsed: " << T.elapsed() << "\n";

If I use the loop at the commented line, instead of
std::cin, the timer works as expected. I can't figure out
what's wrong here.

I run this code and I get numbers output such as 3.0532

I'm using VC++ 2003

That's a known bug in VC++ (or maybe the Windows runtime
libraries---I'm not sure at what level it occurs). If you get
anything but 0 for a keyboard wait, you're implementation is
incorrect (or the underlying system simply doesn't keep track of
the information).


MSDN for clock function says this:
ANSI The era for the clock function
The clock function's era begins (with a value of 0) when the C program
starts to execute. It returns times measured in 1/CLOCKS_PER_SEC (which
equals 1/1000 for Microsoft C).

I take it that there's supposed to be more to it than that then?

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