Microtime() Equivalent for C and C++?

问题:

I am wondering if there is an equivalent to the PHP function microtime() in C and C++. I looked around but couldn't find a definitive answer.

Thanks!

回答1:

On Linux, you can use gettimeofday, which should give the same information. In fact, I believe that is the function that PHP uses under the covers.

回答2:

There is no exact equivalent to PHP's microtime(), but you could a function with a similar functionality based on the following code:

Mac OS X and probably also Linux/Unix

#include <sys/time.h>
struct timeval time;
gettimeofday(&time, NULL); #This actually returns a struct that has microsecond precision.
long microsec = ((unsigned long long)time.tv_sec * 1000000) + time.tv_usec;

(based on: http://brian.pontarelli.com/2009/01/05/getting-the-current-system-time-in-milliseconds-with-c/)

---

Windows:

unsigned __int64 freq;
QueryPerformanceFrequency((LARGE_INTEGER*)&freq);
double timerFrequency = (1.0/freq);

unsigned __int64 startTime;
QueryPerformanceCounter((LARGE_INTEGER *)&startTime);

//do something...

unsigned __int64 endTime;
QueryPerformanceCounter((LARGE_INTEGER *)&endTime);
double timeDifferenceInMilliseconds = ((endTime-startTime) * timerFrequency);

(answer by Darcara, from: https://stackoverflow.com/a/4568649/330067)

回答3:

C++11 added some standard timekeeping functions (see section 20.11 "Time utilities") with good accuracy, but most compilers don't support those yet.

Mostly you need to use your OS API, such as gettimeofday for POSIX.

回答4:

For timing sections of code, try std::clock, which returns ticks, then divide by CLOCKS_PER_SEC.

回答5:

libUTP (uTorrent Transport Protocol library) has a good example on getting the microtime on different platforms.

回答6:

in c++11 i believe the equivalent to php's microtime(true) is:

#include <chrono>
double microtime(){
    return (double(std::chrono::duration_cast<std::chrono::microseconds>(std::chrono::system_clock::now().time_since_epoch()).count()) / double(1000000));
}

• but i'm not sure what the C equivalent is, or if there even is one (as others have pointed out, gettimeofday is part of posix, but not part of c/c++ specs)

interestingly a microsecond is one millionth of a second, but c++ also supports nanoseconds, which is one BILLIONTH of a second, i guess you'd get higher precision with std::chrono::nanoseconds instead of std::chrono::microseconds, but at that point you'd probably run into max number limits of double, and the function name would be misleading (such a function should have the name nanotime() not microtime(), and the return should probably be something bigger than double), btw i have a collection of php-functions-ported-to-c++ here: https://github.com/divinity76/phpcpp (and microtime() is among them)