c分析面向對象的實現技術

面向對象編程和結構化編程幾乎在同一時期出現。但是由於早些時候的機器環境不允許，如內存、cpu等。導致面向對象技術沒有得到及時的發展，而同時因爲結構化程序對硬件要求不是那麼強烈，所以及時的發展起來了。

但是雖然如此，更多的人在談到面向對象時總覺得是種優越，總覺得"高人一等"，自認爲c++一定比c優秀。下面通過用c來實現對象，也說明它們之間的關係，以及面向對象的本質實現。

在開發用戶管理系統的時候，一般的user類都如此，java實現：

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()); } }  
 
下面通過c的實現展示如何實現面向對象技術： 
 
#include <stdio.h> #include <string.h> #include <stdlib.h> /* * array.c * * Created on: 2009-7-20 * Author: cangyingzhijia * * c模擬面向對象實現 */ 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); /** * 定義方法操作表 */ 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 }; //註冊方法 struct User { String name; String password; String _tostring; //對toString方法構造的空間的引用 struct operation *operator; } profile = { operator:&opt };//聲明一個原形,將來構造對象的時候直接拷貝 #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");//構造函數進行初始化 printf("%s", u->operator->toString(u)); u->operator->destruct(u); //析構函數銷燬對象 return 0; }   
從上面簡單的實現不難看出，面向對象的內部祕密。
在早些時候的c＋＋實現中，c＋＋先編譯成c，再用c編譯器編譯成可執行程序。可以得見結構化語言也能實現對象化的，面向對象也沒有那麼神祕。