关于winapi：C程序输出分析

C program output analysis

在Windows 10上运行的简单C程序。(Visual Studio 2013)

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#include <time.h>

void hello(){
printf("hello world");
}

int _tmain(int argc, _TCHAR* argv[])
{
clock_t t;
for (int i = 0; i<50; i++){
t = clock();
hello();
t = clock() - t;
double time_taken = ((double)t) / CLOCKS_PER_SEC; // in seconds

printf("hello() took %f ms to execute \
", time_taken * 1000);
}
getchar();
return 0;
}

输出：

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hello worldhello() took 0.000000 ms to execute(35times)
hello worldhello() took 17.000000 ms to execute
hello worldhello() took 3.000000 ms to execute
hello worldhello() took 2.000000 ms to execute
hello worldhello() took 0.000000 ms to execute(5 times)
hello worldhello() took 15.000000 ms to execute
hello worldhello() took 0.000000 ms to execute(4 times)
hello worldhello() took 16.000000 ms to execute
hello worldhello() took 0.000000 ms to execute

某些行为0.000000，某些行为15.000000-17.000000

这些输出可能与第二次运行的输出不完全相同。但是在第二/第三次..运行中，必须有一些行包含0.000000ms和15.000000-17.000000ms。

0ms到16ms(是否是进程CPU时间？)。请您解释一下真正的原因是什么。

如果我想避免这种更改并获得0-1 ms之类的统一输出，那么我该如何更改我的代码。 (循环运行了50次，但是如果我运行100次或1000次，则时间效果很容易理解。)