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 -1;
    }

    //创建一个文件映射内核对象;
    HANDLE mapFileH = CreateFileMapping( fileH,
        NULL,
        PAGE_READWRITE,
        0,
        0,
        "Resource " ); 
    if(mapFileH == NULL)
    {
        cout<<"error in CreateFileMapping"<<endl;
        return -1;
    }

    //将文件数据映射到进程的地址空间;
    char * mapH = (char *)MapViewOfFile( mapFileH, 
        FILE_MAP_ALL_ACCESS,
        0,
        0, 
        0); 
    if(mapH == NULL)
    {
        cout<<"error in MapViewOfFile"<<endl;
        return -1;
    }

    //读取数据;
    char *buf = mapH;
    double k;
    int times = 300000*34;
    for(int i = 1; i <= times; i++)
    {
        k = atof(buf);
        buf = strstr(buf+9," ");
        //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 -1;
    }
    for(int i = 1 ;i <= times; i++)
    {
        fscanf(fp,"%lf",&k);
    }
    fclose(fp);

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


    return 0;
}

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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