堆與拷貝構(gòu)造函數(shù)

1、student.h#ifndef STUDENT_H#define STUDENT_Hclass Studentpublic:Student(char* pName="no name",int ssID=0);Student(Student& s);/拷貝構(gòu)造函數(shù)Student();protected:char name40;int id;#endifstudent.cpp#include <iostream>#include <string>#include "student.h"using namespace std;

2、Student:Student(char* pName,int ssID)strcpy(name,pName);cout<<"constructing new student"<<pName<<endl;Student:Student(Student& s) /拷貝構(gòu)造函數(shù)，必須用引用或指針，不能直接用student(student s) /因?yàn)椴荒芟窕緮?shù)據(jù)類型那樣直接傳遞對象的值。 cout<<"constructing copy of"<<<<endl;st

3、rcpy(name,"copy of");strcat(name,);id=s.id;Student:Student()cout<<"destructing"<<name<<endl;/* *test.cpp *堆與拷貝構(gòu)造函數(shù)的測試 *2011/10/7 *劉珅珅*/#include <iostream>#include <string>#include "student.h"using namespace std;void fn(Student s);int

4、main(int argc,char* argv)Student randy("Randy",1234);cout<<"calling fn()n"fn(randy);/要調(diào)用拷貝構(gòu)造函數(shù)cout<<"returned from fn()n" Student jenny=randy;/調(diào)用拷貝構(gòu)造函數(shù)return 0;void fn(Student s)cout<<"In function fn()n"輸出的結(jié)果：有拷貝構(gòu)造函數(shù)：constructing new studentR

5、andycalling fn()constructing copy of RandyIn functiong fn()destructingcopy ofRandy/fn()函數(shù)結(jié)束，發(fā)生析構(gòu)，析構(gòu)的是fn中s對象returned from fn()constructing copy of Randy/拷貝構(gòu)造jenny對象destructingcopy ofRandy/析構(gòu)jenny對象destructingRandy/析構(gòu)了randy對象沒有拷貝構(gòu)造函數(shù)：constructing new studentRandycalling fn()In functiong fn()/當(dāng)沒有自定義拷貝構(gòu)

6、造函數(shù)時(shí)，C+會(huì)調(diào)用默認(rèn)的拷貝構(gòu)造函數(shù)/但類擁有資源時(shí)，采用默認(rèn)的拷貝構(gòu)造函數(shù)容易出問題destructingRandy/fn()函數(shù)，發(fā)生析構(gòu)，析構(gòu)對象sreturned from fn()destructingRandy/析構(gòu)對象jennydestructingRandy用一個(gè)類對象區(qū)構(gòu)造一個(gè)新的對象時(shí)，如果沒有自定義的拷貝構(gòu)造函數(shù)，C+會(huì)調(diào)用默認(rèn)的拷貝構(gòu)造函數(shù)，但如果構(gòu)造函數(shù)中有資源（堆內(nèi)存）時(shí)，會(huì)出問題，因?yàn)槟J(rèn)的拷貝構(gòu)造函數(shù)只會(huì)簡單的拷貝資源，而不會(huì)分配資源，這時(shí)會(huì)出現(xiàn)：兩個(gè)對象都擁有同一個(gè)資源的局面，在析構(gòu)時(shí)會(huì)產(chǎn)生錯(cuò)誤。這時(shí)需要自定義拷貝構(gòu)造函數(shù)做深拷貝。person.h#ifnd

7、ef PERSON_H#define PERSON_Hclass Personpublic:Person(char* pN);Person(Person& p);/拷貝構(gòu)造函數(shù)Person();protected:char* pName;#endifperson.cpp#include <iostream>#include <string>#include "person.h"using namespace std;Person:Person(char* pN)cout<<"constructing "<

8、<pN<<endl;pName=new charstrlen(pN)+1;if(pName!=0)strcpy(pName,pN);Person:Person(Person& p)/* *這個(gè)拷貝構(gòu)造函數(shù)是必須的，原因是析構(gòu)函數(shù)中使用deltete將堆空間返回給系統(tǒng) *如果沒有拷貝構(gòu)造函數(shù)，而使用默認(rèn)的拷貝構(gòu)造函數(shù)，那么后面的程序中p1,p2將擁有完全相同的堆空間，在析構(gòu)時(shí)，析構(gòu)了p2后，堆空間已經(jīng)返回給系統(tǒng)，再析構(gòu)p1時(shí)，執(zhí)行delete pName;就會(huì)出錯(cuò)*/cout<<"Copying"<<p.pName<&l

9、t;"into its own blockn"pName=new charstrlen(p.pName)+1;if(pName!=0)strcpy(pName,p.pName);Person:Person()cout<<"destructing"<<pName<<endl;pName0='0'delete pName; test.cpp/* *test.cpp *堆與拷貝構(gòu)造函數(shù)的測試 *2011/10/7 *劉珅珅*/#include <iostream>#include <string>#include "person.h"using namespace std;int main(int argc,char* arg