C语言 文件映射

文件映射内存(虚拟内存)


    处理大数据在内存不够用时，可以通过文件映射来加速

    映射后的长度不可以通过realloc来修改

    #include <stdio.h>
    #include <stdlib.h>
    #include <windows.h>

    char path[128] = "c:\\eli.txt";

    int main()
    {
        //打开一个文件
        HANDLE hfile = CreateFileA(path, GENERIC_READ | GENERIC_WRITE, 0, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);

        if (hfile == INVALID_HANDLE_VALUE)
        {
            printf("打开文件失败\n");
            system("pause");
            exit(0);
        }
        //获取文件大小
        unsigned int filesize = GetFileSize(hfile, NULL);

        printf("文件长度:%d\n", filesize);

        HANDLE hmap = CreateFileMappingA(hfile, //文件映射
            NULL,
            PAGE_READWRITE | SEC_COMMIT,
            0,
            filesize + 1,
            NULL);

        if (hmap == NULL)
        {
            printf("映射失败\n");
            CloseHandle(hfile);
            system("pause");
            exit(0);
        }

        //创建一个指针，存储映射以后的首地址
        PVOID pvfile = MapViewOfFile(hmap, FILE_MAP_READ | FILE_MAP_WRITE, 0, 0, 0);

        if (hmap == NULL)
        {
            printf("指针映射失败\n");
            CloseHandle(hfile);
            CloseHandle(hmap);
            system("pause");
            exit(0);
        }

        printf("文件映射成功\n");

        char *pstart = pvfile; //首地址
        char *pend = pstart + filesize; //结束地址
        system("pause");
        int i;

        // 从映射的文件中读内容
        for (i = 0; i < 200; i++)
        {
            putchar(*(pstart + i));
        }

        printf("\n");
        system("pause");

        UnmapViewOfFile(pvfile);
        CloseHandle(hfile);
        CloseHandle(hmap);
        CloseHandle(hfile);

        system("pause");
        return 0;
    }