CallNtPowerInformation函数失败，返回值为STATUS_BUFFER_TOO_SMALL

Question

这是我的代码，我发现a的值永远不会改变，然后我检查返回值，它是STATUS_BUFFER_TOO_SMALL

#include "stdafx.h"
#include <Windows.h>  
extern "C" {
#include <Powrprof.h>
}
#pragma comment(lib, "Powrprof.lib")
typedef struct _PROCESSOR_POWER_INFORMATION {
    ULONG  Number;
    ULONG  MaxMhz;
    ULONG  CurrentMhz;
    ULONG  MhzLimit;
    ULONG  MaxIdleState;
    ULONG  CurrentIdleState;
} PROCESSOR_POWER_INFORMATION, *PPROCESSOR_POWER_INFORMATION;

int main(int argc, char* argv[])
{

    PROCESSOR_POWER_INFORMATION a;
    while (1)
    {
        CallNtPowerInformation(ProcessorInformation, NULL, 0, &a, sizeof(a));       
    }

    system("pause");
    return 0;
}

OutputBufferSize是sizeof（a），但为什么它会返回STATUS_BUFFER_TOO_SMALL，以及如何修复它？