c分析面向对象的实现技术

面向对象编程和结构化编程几乎在同一时期出现。但是由于早些时候的机器环境不允许，如内存、cpu等。导致面向对象技术没有得到及时的发展，而同时因为结构化程序对硬件要求不是那么强烈，所以及时的发展起来了。

但是虽然如此，更多的人在谈到面向对象时总觉得是种优越，总觉得"高人一等"，自认为c++一定比c优秀。下面通过用c来实现对象，也说明它们之间的关系，以及面向对象的本质实现。

在开发用户管理系统的时候，一般的user类都如此，java实现：

public class User { String name; String password; public User(String n, String pwd) { this.setName(n); this.setPassword(pwd); } public String getName() { return this.name; } public String getPassword() { return this.password; } public void setName(String n) { this.name = n; } public void setPassword(String pwd) { this.password = pwd; } public String toString(){ return "name:" + this.getName() + ",password:" + this.getPassword(); } public static void main(String[] args) { User u = new User("abc","456"); System.out.println(u.toString()); } }  
 
下面通过c的实现展示如何实现面向对象技术： 
 
#include <stdio.h> #include <string.h> #include <stdlib.h> /* * array.c * * Created on: 2009-7-20 * Author: cangyingzhijia * * c模拟面向对象实现 */ struct User; typedef char * String; static String _toString(struct User *this); static String _getPassword(struct User *this); static String _getName(struct User *this); static void _setName(struct User *this, String n); static void _setPassword(struct User *this, String pwd); static void _construct(struct User *this, String n, String pwd); static void _destruct(struct User *this); /** * 定义方法操作表 */ static struct operation { void (*construct)(struct User *this, String n, String pwd); void (*destruct)(struct User *this); String (*toString)(struct User *this); String (*getPassword)(struct User *this); String (*getName)(struct User *this); void (*setName)(struct User *this, String n); void (*setPassword)(struct User *this, String pwd); } opt = { toString:_toString, getPassword:_getPassword, getName:_getName, setName:_setName, setPassword:_setPassword, construct:_construct, destruct:_destruct }; //注册方法 struct User { String name; String password; String _tostring; //对toString方法构造的空间的引用 struct operation *operator; } profile = { operator:&opt };//声明一个原形,将来构造对象的时候直接拷贝 #define new(type) (type *)memcpy(calloc(1,sizeof(type)),&profile,sizeof(profile)) static String _toString(struct User *this) { if (this->_tostring != NULL) { free(this->_tostring); } int len = strlen(this->operator->getName(this)); len += strlen(this->operator->getPassword(this)); len += strlen("name:,password:"); this->_tostring = calloc(1, len + 1); snprintf(this->_tostring, len, "name:%s,password:%s", this->operator->setName(this), this->operator->getPassword(this)); return this->_tostring; } static String _getPassword(struct User *this) { return this->password; } static String _getName(struct User *this) { return this->name; } static void _setName(struct User *this, String n) { if (this->name != NULL) { free(this->name); } int len = strlen(n); this->name = calloc(1, len + 1); memcpy(this->name, n, len); } static void _setPassword(struct User *this, String pwd) { if (this->password != NULL) { free(this->password); } int len = strlen(pwd); this->password = calloc(1, len + 1); memcpy(this->password, pwd, len); } static void _construct(struct User *this, String n, String pwd) { this->operator->setName(this, n); this->operator->setPassword(this, pwd); } static void _destruct(struct User *this) { free(this->name); free(this->password); free(this); } int main() { struct User *u = new(struct User); u->operator->construct(u, "abc", "456");//构造函数进行初始化 printf("%s", u->operator->toString(u)); u->operator->destruct(u); //析构函数销毁对象 return 0; }   
从上面简单的实现不难看出，面向对象的内部秘密。
在早些时候的c＋＋实现中，c＋＋先编译成c，再用c编译器编译成可执行程序。可以得见结构化语言也能实现对象化的，面向对象也没有那么神秘。