C++中使用内存映射文件存取struct,并用指针访问

#include <iostream>
#include <Windows.h>

#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;
	}
}

posted @ 2011-05-19 09:10  玉开  阅读(3356)  评论(0编辑  收藏  举报