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：

c++ windows下读取大文件（内存映射）-LMLPHP