Hello,OOC World![Chap2Sec1-3][GFDL]

pingf posted @ Sat, 28 May 2011 20:24:56 -1100 in 未分类 , 3115 readers

项目地址(点击超链)　OOC_GCC

注意:OOC_GCC 源码以LGPL发布,文档为GFDL,文档相关测试用例为GPL3

Web版文档发布暂定为项目托管地SVN仓库,WikiPage,"这里",以及我的博客.

转载请注明出处

Hello，OOC World!

                ---- 原始作者: 大孟  pingf0@gmail.com

                                          崇 尚 开 源 , 热 爱 分 享 !

这份Tutorial性质的文档其实很扯的,非要啰嗦些用C语言进行面向对象开发的基本内容

版权说明

License Type: GFDL

Copyright (C) 2011-2011 Jesse Meng pingf0@gmail.com
Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation;with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.A copy of the license is included in the section entitled “GNU Free Documentation License”.

OOC-GCC为开源软件,遵循LGPL3协议发布,本手册为相关配套文档,采用GFDL协议发布,本手册中提供的相关示例代码以及简化版的OOC-LITE 需遵循GPL3协议.任何使用请遵循相关协议, 如有和协议相冲突的特殊要求, 请联系我[ pingf0@gmail.com ]

第二章 { 伸展运动 }

1. < CLASS,CTOR,DTOR >

宏是一个十分强大的特性,某些人的观点是通过宏实际上我们可以创立一个新的语言!当然个人认为只是形式上罢了.不过通过宏,代码看起来真的可以很简洁,很强大.比如下面所介绍的,将用一些简单的宏让C代码看上去有点C++的味道.


#include "OOC.h"
CLASS(A){
        int a;
        void (*showA)(A *);
};
static void A_showA(A *THIS){
        printf("the value of obj's a is %d\n",THIS->a);
}
CTOR(A){
        THIS->a=100;
        THIS->showA=A_showA;
}
DTOR(A){
        THIS->a=0;
        THIS->showA=NULL;
}
int main(){
        A * obj=newA();
        obj->showA(obj);
        delA(&obj);
        return 0;
}

这个例子中用到了三个宏,分别是CLASS,CTOR(对应CONSTRUCTOR),DTOR(对应DESTRUCTOR). 如果把他们展开,其实和前面"对称之美"一节中的代码是一样的.但又不一样,因为使用了宏,可读性大大提高, 而代码量大大减少(上面的代码和上一章中的对比减少了约1/3)!这只是一个简单的类的模拟,如果类比较多且继生关系比较复杂, 那么节省的代码量还是相当可观的.

不过这里还是要再次强调一下,宏是好东西,但如果滥用反而会使可读性大大降低,难懂不说,还不利于以后的维护.

关于本手册中的宏的设计,我尽量做到简单明了,易于记忆.

闲话少扯,现在具体来看一下CLASS,CTOR和DTOR宏具体是怎么实现的.

#include <stdio.h>
#include <stdlib.h>
#define CLASS(Type) \
typedef struct _##Type Type; \
void ini##Type(struct _##Type *); \
void fin##Type(struct _##Type *); \
Type * new##Type(); \
void del##Type(struct _##Type **); \
struct _##Type

#define CTOR(Type) \
Type * new##Type() { \
    Type *THIS; \
    THIS=(Type*)calloc(1,sizeof(Type)); \
    if( NULL==THIS ) { \
        return NULL; \
    } \
    ini##Type(THIS); \
    return THIS; \
} \
void ini##Type(Type * THIS)

#define DTOR(Type) \
void del##Type(Type **THIS) { \
    fin##Type(*(THIS)); \
    free(*(THIS)); \
    (*(THIS))=NULL; \
} \
void fin##Type(Type *THIS)

没错,就是这么简单!(当然如果你觉得这都算复杂了话,还是不要继续下面的文字了,这是我目前能做到的最简化的宏了)

下一节将会闲扯一些为什么这样设计,以及仅仅是这样还有那些不足.

2. < 从CLASS说起 >

C语言中直接使用结构体其实是件很麻烦的事,因为每次声明都要使用额外的"struct"来声明.一些初学C的人,特别从VC开始入门那些,总会分不清什么是C,什么是C++.特别是在struct声明这一块也特别容易按照懒省事儿的方法来写.但是我们应该知道一些事情----真正的纯C编译器如果不事先typedef一下是无法声明一个自定的结构体的实例的.

下面看一小段代码,演示如何将typedef与struct来结合.

typedef struct {int a;} A;
int main(){
        A obj;
        ojb.a=1;
        return 0;
}

关于typedef的语法,如果不牵扯结构体,是比较好理解的,比如"typedef int bool;"就是将原有的int型重定义为一个全新的bool型,尽管本质上它们是一样的.而一旦与结构体结合,就略微有些绕了.为了简化说明它的语法,上面的代码我做了一些处理,一是结构体本身匿名话,二是简化结构体内容并将其写到一行之内.这样我们看上去会十分明了还是"typedef struct ... A;"的形式,而"..."中我们其实定义了一个结构体的内容,只不过这个结构体本身是"匿名的".

更加常规的写法是,像下面这样.

typedef struct _A A;
struct _A{
        int a;
};
int main(){
        A obj;
        ojb.a=1;
        return 0;
}

在CLASS宏中,也使用了和上面类似的做法来简化struct声明实例时的步骤.

#define CLASS(Type) \
typedef struct _##Type Type; \
void ini##Type(struct _##Type *); \
void fin##Type(struct _##Type *); \
Type * new##Type(); \
void del##Type(struct _##Type **); \
struct _##Type

CLASS宏不但简化了struct声明实例的工作,还声明了"四大函数"(将函数声明放在最前面是有好处的,它会让编译器在一开始就知道有这么些类型的函数).这四个函数其实是"两队",一对是ini和fin打头,另一对是new和del打头.其分别对应栈内存和堆内存上实例的构造与析构.

而CLASS宏的最后则是一个全开放的形式(这里的全开放是指某个宏不需要语气配合相对应的"截止"宏来保护一段代码),开头和结尾都是用C语言自身的"{"和"}"符合来指明.

在下一节,将会介绍用于构造和析构的CTOR和DTOR宏,而它们则封装了"四大函数"的具体实现.

3. < CTOR & DTOR >

这一节来说一下用于模拟构造函数的宏CTOR以及用于模拟析构函数的宏DTOR.先回顾下CTOR的定义.

#define CTOR(Type) \
Type * new##Type() { \
    Type *THIS; \
    THIS=(Type*)calloc(1,sizeof(Type)); \
    if( NULL==THIS ) { \
        return NULL; \
    } \
    ini##Type(THIS); \
    return THIS; \
} \
void ini##Type(Type * THIS)

假设我们还是要定义一个名为"A"的类,那么上面的代码中我们要把"Type"换成"A",并删除"##"(注意##在宏的使用中表示"连结").这样的话,我们就看到了一个完整的"newA"函数和一个没有写完的"iniA"函数(请参考上一节最后的"四大函数"一说).

"iniA"函数实际上是真正的构造函数,其负责一个"类"成员的初始化.但其没有写完,因为具体如何初始化是由我们自己说了算的,我们可以在其后面紧跟着写上"{ THIS->a=1; }"(假设A类中有int型成员变量a),这样就完成了一个简单的构造函数的实现.

我们要注意的是iniA函数要接受一个类实例指针,然后再对其进行初始化.也就是说这个函数本身是不涉及内存的分配的,我们可以传入一个指向栈内存的指针,也可以传入一个指向堆内存的指针,它都会对其进行"初始化"!但是如果我们使用堆内存,还要先定义一个指针,并指向一块malloc返回的内存再传入ini函数,这多少有些麻烦.为了方便的使用堆内存,上面的CTOR宏还给出了一个new函数,这里仍以一个名为"A"的类为例.newA就将malloc函数和iniA函数和二为一!我们使用的时候只需像"A * obj=newA();"这样即可,这大大方便了堆实例的使用!

不难发现,newA就是对iniA的一个简单封装,其做的工作就是"1.分配堆内存.2.调用ini函数.3.返回一个指向已分配内存的指针."这三块工作,这是有章可循的.也正因此,我们将其完全封装在CTOR宏之中.使用的时候我们几乎感觉不到它的存在,直接new就好.

下面再来看一下用于析构的DTOR宏,

#define DTOR(Type) \
void del##Type(Type **THIS) { \
    fin##Type(*(THIS)); \
    free(*(THIS)); \
    (*(THIS))=NULL; \
} \
void fin##Type(Type *THIS)

这里面定义了"四大函数"中用于析构的del函数和fin函数.其分别对应着前面的new函数和ini函数.我们可以对比着前面的讲述来理解.ini函数是真正的构造函数,fin函数是真正的析构函数.new是ini函数的一个封装,其做的具体工作就是先malloc在ini,del则是fin函数的一个封装,其做的具体工作是先fin再free.

当然因为有了new函数和del函数这样针对堆内存的封装,ini函数和fin函数更多的时候是与栈内存来配合使用的.

总的来看CTOR宏和DTOR宏,将涉及内存分配的部分独立出来可谓好处多多,不但可以更加自由且明确的使用栈内存和堆内存,还使得用于构造和析构的宏也能保持和前面CLASS宏一样的"全开放性",同时CTOR宏和DTOR宏几乎是完全对称的,这意味着我们只需理解一半,另一半就迎刃而解了.

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