C语言模拟虚基类 - 模拟lighttpd fdevent实现

看了lighttpd中的fdevent的实现过程有些巧妙，写个例子模拟它的的实现：

虚基类是fdos（os操作系统，fd是随便加的没什么意义），它有三个派生类分别是：windows, linux, mac，

它们的都有的public方法是：open, close, playgame。

/// fdos.h#ifndef FDOS_H_INCLUDED#define FDOS_H_INCLUDEDtypedef enum{    OS_UNSET = -1,    OS_WINDOWS,    OS_LINUX,    OS_MAC}fd_type;typedef struct fdos{    fd_type type;    int maxfds;    int (*open)(struct fdos *os);    void (*close)(struct fdos *os);    void (*playgame)(struct fdos *os, char *name);}fdos;// publicfdos* fdos_init(fd_type type, int maxfds);void fdos_free(fdos *os);int fdos_open(fdos *os);void fdos_close(fdos *os);void fdos_playgame(fdos *os, char *name);// privateint fdos_windows_init(fdos *os);int fdos_linux_init(fdos *os);int fdos_mac_init(fdos *os);#endif // FDOS_H_INCLUDED

/// fdos.cpp#include "fdos.h"#include <stdio.h>#include <stdlib.h>fdos* fdos_init(fd_type type, int maxfds){    fdos *os;    os = (fdos*)malloc(sizeof(*os));    os->maxfds = maxfds;    switch (type)    {        case OS_WINDOWS:        if (0 != fdos_windows_init(os))        {            printf("windows init fail\n");            return NULL;        }        return os;        case OS_LINUX:        if (0 != fdos_linux_init(os))        {            printf("linux init fail\n");            return NULL;        }        return os;        case OS_MAC:        if (0 != fdos_mac_init(os))        {            printf("mac init fail\n");            return NULL;        }        return os;        case OS_UNSET:        break;    }    printf("fdos init fail\n");    return NULL;}void fdos_free(fdos *os){    if (os)    {        free(os);    }}int fdos_open(fdos *os){    return os->open(os);}void fdos_close(fdos *os){    return os->close(os);}void fdos_playgame(fdos *os, char *name){    return os->playgame(os, name);}

/// fdwindows.cpp#include "fdos.h"#include <stdio.h>static int fdos_windows_open(fdos *os){    printf("windows open\n");    return 0;}static void fdos_windows_close(fdos *os){    printf("windows close\n");}static void fdos_windows_playgame(fdos *os, char *name){    printf("windows playgame: %s\n", name);}int fdos_windows_init(fdos *os){    os->type = OS_WINDOWS;    // x作为宏参数，##x则表示连接宏参数    // 如果是#x, 则表示是一个字符串，如：    // #define MY_CONST(x) #x    // printf("%s", MY_CONST(hello));    // 输出:hello#define SET(x) \    os->x = fdos_windows_##x;    // 相当于：fdos_windows_open    SET(open);    // 相当于：fdos_windows_close    SET(close);    // 相当于：fdos_windows_playgame    SET(playgame);    return 0;}

/// fdlinux.cpp#include "fdos.h"#include <stdio.h>static int fdos_linux_open(fdos *os){    printf("linux open\n");    return 0;}static void fdos_linux_close(fdos *os){    printf("linux close\n");}static void fdos_linux_playgame(fdos *os, char *name){    printf("linux playgame: %s\n", name);}int fdos_linux_init(fdos *os){    os->type = OS_LINUX;#define SET(x) \    os->x = fdos_linux_##x;    SET(open);    SET(close);    SET(playgame);    return 0;}

/// fdmac.cpp#include "fdos.h"#include <stdio.h>static int fdos_mac_open(fdos *os){    printf("mac open\n");    return 0;}static void fdos_mac_close(fdos *os){    printf("mac close\n");}static void fdos_mac_playgame(fdos *os, char *name){    printf("mac playgame: %s\n", name);}int fdos_mac_init(fdos *os){    os->type = OS_MAC;#define SET(x) \    os->x = fdos_mac_##x;    SET(open);    SET(close);    SET(playgame);    return 0;}

/// main.cpp#include <stdio.h>#include <stdlib.h>#include <string.h>#include <unistd.h>#include "fdos.h"/// testint main(void){    fdos *os = fdos_init(OS_WINDOWS, 3);    fdos_open(os);    fdos_playgame(os, "wow");    fdos_close(os);    fdos_free(os);    os = fdos_init(OS_LINUX, 3);    fdos_open(os);    fdos_free(os);    os = fdos_init(OS_MAC, 3);    fdos_playgame(os, "zx");    fdos_free(os);    return 0;}