Windows-API-examples/datetime/windows_epoch.c

#include <windows.h>
#include <wchar.h>

int wmain(void) {

    FILETIME ft = {0};
  
    GetSystemTimeAsFileTime(&ft);

    LARGE_INTEGER li = {0};    

    li.LowPart = ft.dwLowDateTime;
    li.HighPart = ft.dwHighDateTime;

    long long int hns = li.QuadPart;
    
    wprintf(L"%lli hundreds of nanoseconds have elapsed " 
        "since Windows API epoch\n", hns);

    return 0;
}