c++ windows下读取大文件（内存映射）

关于内存映射的基本知识以及一些函数的原型说明，参考博客：http://blog.csdn.net/wcyoot/article/details/7363393

下面是我对于读取一个104M文件大小，使用内存映射和传统的读文件方法进行了时间上的对比，两种方法都从该文讲读取300000*34个浮点数。

测试环境：vs2010

 #include<iostream>
 #include <cstringt.h>
 #include<vector>
 #include<windows.h>
 #include <ctime>
 using namespace std;

 int main()
 {
     clock_t start, finish;
     //------------------------------------------------------内存映射方法;
     start = clock();
     //创建或打开文件内核对象;
     HANDLE fileH = CreateFile("ldFeature.txt",
         GENERIC_READ|GENERIC_WRITE,
         FILE_SHARE_READ,
         NULL,
         OPEN_EXISTING,
         FILE_ATTRIBUTE_NORMAL,
         NULL);
     if(fileH == INVALID_HANDLE_VALUE)
     {
         cout<<"error in CreateFile"<<endl;
         return -;
     }

     //创建一个文件映射内核对象;
     HANDLE mapFileH = CreateFileMapping( fileH,
         NULL,
         PAGE_READWRITE,
         ,
         ,
         "Resource " );
     if(mapFileH == NULL)
     {
         cout<<"error in CreateFileMapping"<<endl;
         return -;
     }

     //将文件数据映射到进程的地址空间;
     char * mapH = (char *)MapViewOfFile( mapFileH,
         FILE_MAP_ALL_ACCESS,
         ,
         ,
         );
     if(mapH == NULL)
     {
         cout<<"error in MapViewOfFile"<<endl;
         return -;
     }

     //读取数据;
     char *buf = mapH;
     double k;
     int times = *;
     for(int i = ; i <= times; i++)
     {
         k = atof(buf);
         buf = strstr(buf+," ");
         //cout<<k<<endl;
     }
     //关闭句柄;
     UnmapViewOfFile(mapH);
     CloseHandle(mapFileH);
     CloseHandle(fileH); 

     finish = clock();
     //打印耗时;
     cout<<"time:"<<(double)(finish - start)/ CLOCKS_PER_SEC<<endl;

     //------------------------------------------------------传统方法;
     start = clock();

     FILE *fp = fopen("ldFeature.txt","r");
     if(fp == NULL)
     {
         cout<<"error in fopen"<<endl;
         return -;
     }
     for(int i =  ;i <= times; i++)
     {
         fscanf(fp,"%lf",&k);
     }
     fclose(fp);

     finish = clock();
     cout<<"time:"<<(double)(finish - start)/ CLOCKS_PER_SEC<<endl;

     return ;
 }

结果显示，传统方法耗时是内存映射方法的2倍左右。实际上文件越大，使用内存映射方法的优势越明显：

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