C++中使用内存映射文件存取struct，并用指针访问

#include

#include

  

#define OK 0

#define MMF_FILE_SIZE (1024*512)

  

const char* mmf_file_name = "d:\\mmf.txt";

const char* mmf_share_name = "testmmf";

  

//定义内存映射文件相关的全局变量

HANDLE file_handle      = NULL;

HANDLE mfile_handle     = NULL;

void* mview_ptr         = NULL;

  

//打开内存映射文件和映射视图

int open_mmf();

  

//关闭内存映射文件相关资源

void close_mmf();

  

//定义指针

struct Foo{

    unsigned int id;

    char code[30];

    char name[30];

};

  

  

using namespace std;

  

int main(){

    int open_status = open_mmf();

    if(open_status){

        cout<<"打开内存映射文件出错，错误号："<<open_status<<endl;

    }else{

        cout<<"成功打开了内存映射文件"<<endl;

  

        Foo* foo_ptr = (Foo*)mview_ptr;

        Foo foo;

          

        const size_t foo_size = sizeof(Foo);

        int count = MMF_FILE_SIZE / foo_size - 1;

        for(int i=0;i<=count;i++){

            foo.id = i+1;

            sprintf(foo.name,"+%d",foo.id);

            sprintf(foo.code,"-%d",foo.id);

            memcpy(foo_ptr+i,&foo,foo_size);

              

            printf("copy %d\r",i);

        }

  

        cout<<"保存数据完毕"<<endl;

  

        cout<<"尝试读取数据"<<endl;

        for(int i=0;i<=count;i++){

            foo = *(foo_ptr+i);

  

            cout<<"foo:"<<foo.id<<","<<foo.code<<","<<foo.name<<endl;

        }

        cout<<"读取数据完毕"<<endl;

    }

  

    system("pause");

    close_mmf();

    return EXIT_SUCCESS;

}

  

  

  

  

  

//打开内存映射文件

int open_mmf(){

    file_handle = CreateFile(mmf_file_name,

        GENERIC_ALL,

        FILE_SHARE_READ|FILE_SHARE_WRITE,

        NULL,

        OPEN_ALWAYS,

        FILE_FLAG_SEQUENTIAL_SCAN,

        NULL);

  

    if(INVALID_HANDLE_VALUE == file_handle){

        return GetLastError();

    }

  

  

    mfile_handle = CreateFileMapping(file_handle,

        NULL,

        PAGE_READWRITE,

        0,

        MMF_FILE_SIZE,

        mmf_share_name);

  

    if(INVALID_HANDLE_VALUE == mfile_handle){

        return GetLastError();

    }

  

    mview_ptr = MapViewOfFile(mfile_handle,

        FILE_MAP_ALL_ACCESS,

        0,

        0,

        MMF_FILE_SIZE);

  

    return OK;

}

  

//释放内存映射文件占用的资源。

void close_mmf(){

    if(NULL != mview_ptr){

        UnmapViewOfFile(mview_ptr);

        mview_ptr = NULL;

    }

  

    if(NULL != mfile_handle){

        CloseHandle(mfile_handle);

        mfile_handle = NULL;

    }

  

    if(NULL != file_handle){

        CloseHandle(file_handle);

        file_handle = NULL;

    }

}