Precision of the Sleep() Function in Windows C

I rarely use C on Windows for real projects, and this time it bit me.

I had the following test program. I wanted to do a simple library test. Sleep() is said to provide millisecond-level delays, so I naturally used 1 ms to drive it.

while(1)
    {
        MBx_Ticks(1000);  // 换算为微秒传入MBx驱动
        TestMemUpdate(1); // 毫秒传入测试函数
        Sleep(1);
    }

That was, of course, completely inaccurate — as unreliable as Python. You can add the following code to measure the actual delay.

#include <windows.h>
#include <time.h>
SYSTEMTIME t1;

while(1)
    {
        MBx_Ticks(1000);  // 换算为微秒传入MBx驱动
        TestMemUpdate(1); // 毫秒传入测试函数
        Sleep(1);
        /* 打印毫秒时间戳 */
        GetSystemTime(&t1);
        printf("%ld\n", (int)t1.wMilliseconds);
    }

Here is a short excerpt. You can see it's far from 1 ms, but for testing it doesn't matter.