C++ 读取二进制文件速度测试

一个二进制文件里有n 个数据，我想要随机读取K个 数据，并存储在内存中。

void  CDataToPyramid::CompareReadingSpeed()
{


        time_t rawtime;
        struct tm*timeinfo;
        time(&rawtime);
        timeinfo=localtime(&rawtime);
        char *nowtime=asctime(timeinfo);
        TCHAR Name[100];

   MultiByteToWideChar(CP_ACP, 0, nowtime, -1, Name, 100);
         OutputDebugString(Name);
         //Sleep(3000);
        int pensity=5;
        float proportion=(float)pensity/10;

        char *path1="D:\\Data\\ReadSpeedTest\\10_14806_132001.dat";
    FILE *mfile=fopen(path1,"rb+");
        if(mfile!=NULL)
        {
                Head head;
                fread(&head,sizeof(Head),1,mfile);
                int count=head.count;
                int Knum=proportion*count;
         CPoints *Cdata=(CPoints*)malloc(sizeof(CPoints)*Knum);
                int* Iarray=new int[Knum];
                ChouXi(Iarray,Knum,count);
                for(int j=0;j<Knum;j++)
                {
                        //*****测试一 随机读取  所需时间20 s
                        /*
                        int xuhao=Iarray[j];
                        if(j==0)
                        {

                        }
                        else
                        {
                                int offset=(Iarray[j]-Iarray[j-1])*sizeof(CPoints);
                                fseek(mfile,offset,1);  //文件指针 偏移量  时间差主要消耗在这里！！！！！！！！！！！
                        }
                        CPoints Ipt;
                        fread(&Ipt,sizeof(CPoints),1,mfile);
                        memcpy((CPoints*)Cdata+j,&Ipt,sizeof(CPoints));
                        */
                        //******测试二 顺序读取  所需时间6s
                        CPoints Ipt;
                        fread(&Ipt,sizeof(CPoints),1,mfile);
                        memcpy((CPoints*)Cdata+j,&Ipt,sizeof(CPoints));

                }

                fclose(mfile);

        }
        time_t rawtime1;
        struct tm*timeinfo1;
        time(&rawtime1);
        timeinfo1=localtime(&rawtime1);
        char *nowtime1=asctime(timeinfo1);
        TCHAR Name1[100];

   MultiByteToWideChar(CP_ACP, 0, nowtime1, -1, Name1, 100);
         OutputDebugString(Name1);
        MessageBox(NULL,_T("OVER"),_T("OVER"),NULL);
}
int  CDataToPyramid::bigrand()
{

        return RAND_MAX*rand()+rand();

}
void CDataToPyramid::ChouXi(int* cc,int K,int totalcount)
{
    // 在totalcount 数中，随机产生K个不相同的数
        int index=0;
        if(K!=totalcount)
        {
                for(int i=0;K>0&&i<totalcount;i++)
                {
                        if((bigrand()%(totalcount-i))<K)
                        {
                                cc[index]=i;
                                index++;
                                K--;
                        }

                }


        }
        

}