Re: elapsed time 0 with std::cin

"James Kanze" <james.ka...@gmail.com> wrote in message
 news:ef3426bb-2220-430c-ae95-6b5f109d0423@j20g2000hsi.googlegroups.com...=

 On Nov 23, 9:43 pm, "Jim Langston" <tazmas...@rocketmail.com> wrote:
 > "pekka" <pe...@nospam.invalid> wrote in message
     [...]
 > > Here's my code:
 > > #include <ctime>
 > > #include <iostream>
 > > #include <string>
 > > class Timer
 > > {
 > > clock_t start_, nticks_;
 > > public:
 > > 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;
 > > T.stop();
 > > 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 4.12.2.1 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?