GlobalMemoryStatusEx
获得系统时间： 
CopyBOOL WINAPI GetSystemTimes(
  __out_opt  LPFILETIME lpIdleTime,   //空闲时间
  __out_opt  LPFILETIME lpKernelTime, //内核时间
  __out_opt  LPFILETIME lpUserTime    //用户时间
);

#define _WIN32_WINNT   0x0501
#include <Windows.h>
#include <iostream> 
using   namespace   std;

__int64 CompareFileTime ( FILETIME time1, FILETIME time2 )
{
       __int64 a = time1.dwHighDateTime << 32 | time1.dwLowDateTime ;
       __int64 b = time2.dwHighDateTime << 32 | time2.dwLowDateTime ;

       return   (b - a);
}
void main() 
{ 
HANDLE hEvent;
BOOL res ;

FILETIME preidleTime;
FILETIME prekernelTime;
FILETIME preuserTime;

FILETIME idleTime;
FILETIME kernelTime;
FILETIME userTime;

res = GetSystemTimes( &idleTime, &kernelTime, &userTime );

preidleTime = idleTime;
prekernelTime = kernelTime;
preuserTime = userTime ;

hEvent = CreateEvent (NULL,FALSE,FALSE,NULL); // 初始值为 nonsignaled ，并且每次触发后自动设置为nonsignaled

while (1){
      WaitForSingleObject( hEvent,1000 ); //等待500毫秒
      res = GetSystemTimes( &idleTime, &kernelTime, &userTime );
     
       int idle = CompareFileTime( preidleTime,idleTime);
       int kernel = CompareFileTime( prekernelTime, kernelTime);
       int user = CompareFileTime(preuserTime, userTime);

int cpu = (kernel +user - idle) *100/(kernel+user);//（总的时间-空闲时间）/总的时间=占用cpu的时间就是使用率
     int cpuidle = ( idle) *100/(kernel+user);
     cout << "CPU利用率:" << cpu << "%" << "      CPU空闲率:" <<cpuidle << "%" <<endl;

preidleTime = idleTime;
    prekernelTime = kernelTime;
    preuserTime = userTime ;
    }
}

接口是在 Winbase.h 文件中声明的，声明如下：
#if _WIN32_WINNT >= 0x0501

BOOL
WINAPI
GetSystemTimes(
    LPFILETIME lpIdleTime,
    LPFILETIME lpKernelTime,
    LPFILETIME lpUserTime
    );

#endif // (_WIN32_WINNT >= 0x0501)

注意，这个宏 #if _WIN32_WINNT >= 0x0501 ，它的意思是，只有当windows版本高于0x0501，也就是WinXP SP1时，声明才有效，原来如此！

修改头文件声明为：
#define _WIN32_WINNT 0x0501
#include <Windows.h>