C++使用内存映射文件入门

本文介绍如何使用CreateFileMapping,MapViewOfFile创建内存映射文件，如何向内存映射文件中写入数据，读取数据。

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#include <iostream>

#include <assert.h>

 

#include <Windows.h>

#include <WinBase.h>

 

#define BAD_POS 0xFFFFFFFF // returned by SetFilePointer and GetFileSize

#define SUCCESS 0

using namespace std;

 

 

typedef DWORD mmf_share_mode;

typedef DWORD mmf_access_mode;

typedef DWORD mmf_flags;

 

 

int main(){

    cout<<"create memorymapfile..."<<endl;

    const char* shared_name = "testMmf";

    const char* file_name = "d:\\testMmf.mmf";

    const DWORD mmf_size = 512*1024;

    //存取模式

    mmf_access_mode access_mode = (GENERIC_READ|GENERIC_WRITE);

    //共享模式

    mmf_share_mode share_mode = FILE_SHARE_READ | FILE_SHARE_WRITE;

    //文件属性

    mmf_flags flags = FILE_FLAG_SEQUENTIAL_SCAN;//|FILE_FLAG_WRITE_THROUGH|FILE_FLAG_NO_BUFFERING;

    DWORD error_code;

     

    //创建文件

    HANDLE mmHandle =

        CreateFile(file_name,

             access_mode,

             share_mode,

             NULL,

             OPEN_ALWAYS,

             flags,

             NULL);

 

    if (mmHandle == INVALID_HANDLE_VALUE) {

        error_code = GetLastError();

        cout<<"创建mmf失败:"<<error_code<<endl;

    }else{

        DWORD high_size;

        DWORD file_size = GetFileSize(mmHandle, &high_size);

        if (file_size == BAD_POS && (error_code = GetLastError()) != SUCCESS) {

            CloseHandle(mmHandle);           

            cout<<"error："<<error_code<<endl;

        }

        cout<<"create mmf sucessfully"<<endl;

 

        //assert(file_size == 0);

 

        DWORD size_high = 0;

        //创建文件映射，如果要创建内存页面文件的映射，第一个参数设置为INVALID_HANDLE_VALUE

        HANDLE mmfm = CreateFileMapping(mmHandle,

            NULL,

            PAGE_READWRITE,

            size_high,

            mmf_size,

            shared_name);

 

        error_code = GetLastError();

        if(SUCCESS != error_code){

            cout<<"createFileMapping error"<<error_code<<endl;

        }else{

            if(mmfm == NULL){

                if(mmHandle != INVALID_HANDLE_VALUE){

                    CloseHandle(mmHandle);

                }

            }else{

                //char write_chars[] = "hello chars";

                //size_t position = 0;

                //DWORD written = 0;

                //const size_t write_chars_size = sizeof(write_chars);

                //WriteFile(mmHandle,write_chars,write_chars_size,&written,NULL);

                size_t view_size = 1024*256;

                DWORD view_access = FILE_MAP_ALL_ACCESS;

 

                //获得映射视图

                char* mmfm_base_address = (char*)MapViewOfFile(mmfm,view_access,0,0,view_size);

                if(mmfm_base_address == NULL){

                    error_code = GetLastError();

                    if(error_code != SUCCESS){

                        cout<<"error code "<<error_code<<endl;

                    }

                }else{

                    char write_chars[] = "hello chars";

                    const size_t write_chars_size = sizeof(write_chars);

                    //向内存映射视图中写数据

                    CopyMemory((PVOID)mmfm_base_address, write_chars, write_chars_size);

 

                    //memcpy(mmfm_base_address,write_chars,write_chars_size);

                     

                    size_t position = 0;

                    char read_chars[write_chars_size];

 

                    //读数据

                    memcpy(read_chars,mmfm_base_address,write_chars_size);

                    cout<<"read chars "<<read_chars<<endl;

                     

                    //卸载映射

                    UnmapViewOfFile(mmfm_base_address);

                    //关闭内存映射文件

                    CloseHandle(mmfm);

                    //关闭文件

                    CloseHandle(mmHandle);

                }

            }

        }

    }

 

     

 

    system("pause");

    exit(0);

    return EXIT_SUCCESS;

}