拷貝構造

#include <iostream>

#include <string.h>

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using namespace std;

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class mystring

{

public:

??? char *s;

public:

??? mystring()

??? {

???????s = new char[1024];

???????cout << "mystring" << endl;

??? }

??? //拷貝構造

??? mystring(const mystring &it)

??? {

???????s= new char[1024];

???????memset(s,0,1024);

???????strcpy(s,it.s);

??? }

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??? ~mystring()

??? {

???????cout << "~mystring" << endl;

??? }

};

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int main()

{

??? mystring str1;

??? strcpy(str1.s,"hello world");

??? //這種方式只調用了一次構造方法

??? mystring str2 = str1;

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//??? mystring str2;

//??? str2 = str1;? //這個過程不是拷貝構造的過程，只是=號操作

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??? cout << str2.s << endl;

??? return 0;

}

運行后的效果是：

當把代碼改成下面的方式的時候，執行結果如下：

#include <iostream> #include <string.h> ? using namespace std; ? class mystring { public: ??? char *s; public: ??? mystring() ??? { ??????? s = new char[1024]; ??????? cout << "mystring" << endl; ??? } ??? //拷貝構造 ??? mystring(const mystring &it) { ??? cout << "copy mystring" << endl; ??????? s= new char[1024]; ??????? memset(s,0,1024); ??????? strcpy(s,it.s); ??? } ? ??? ~mystring() ??? { ??????? cout << "~mystring" << endl; ??????? delete []s; } }; ? int main() { ??? mystring str1; ??? strcpy(str1.s,"hello world"); ??? //這種方式只調用了一次構造方法 ??? //mystring str2 = str1; ? ??? mystring str2; ??? str2 = str1;? //這個過程不是拷貝構造的過程，只是=號操作 ? ??? cout << str2.s << endl; ??? return 0; } str1 = str2的本質

2.操作符重載規則

重載操作符函數可以對操作作出新的解釋，但原有基本予以不變：

A:不改變操作符的優先級

B:不改變操作符的結合性

C:不改變操作符需要的操作數

D:不能創建新的操作符

成員的語法形式為：

???????? 類型 類名：：operator op(參數表)

{

??? //相對于該類定義的操作

}

? 重載賦值操作符

? 賦值操作符重載用于對象數據的復制

? operator= 必須重載為成員函數

? voidoperator = (const classname &it);

?classname &operator = (const classname &it);

? 返回引用會支持如下語法：obj1= obj2 = obj3;

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3.操作符重載的案例：

#include <iostream>

#include <stdlib.h>

#include <string.h>

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using namespace std;

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class mystring

{

public:

??? char *s;

public:

??? mystring()

??? {

???????s = new char[1024];

???????cout << "mystring" << endl;

??? }

??? mystring(const mystring &it)//深拷貝

??? {

???????cout << "copy mystring" << endl;

???????s = new char[1024];

???????memset(s, 0, 1024);

???????strcpy(s, it.s);

??? }

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??? ~mystring()

??? {

???????cout << "~mystring" << endl;

???????delete []s;

??? }

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??? mystring operator =(const mystring &it)//重載了一個=號操作符

??? {

???????cout << "= operator" << endl;

???????memset(s, 0, 1024);

???????strcpy(s, it.s);

???????//在這個過程中調用了深拷貝的過,這里是以個臨時的拷貝過程，拷貝完成之后調用深拷貝

???????return *this;

??? }

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??? mystring operator =(const char *str)//重載了一個=號操作符

??? {

???????memset(s, 0, 1024);

???????strcpy(s, str);

???????return *this;

??? }

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??? mystring operator =(int i)//重載了一個=號操作符

??? {

???????memset(s, 0, 1024);

???????sprintf(s, "%d", i);

???????return *this;

??? }

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??? mystring operator + (const mystring &it)//重載了一個+號操作符

??? {

???????strcat(s, it.s);

???????return *this;

??? }

?

??? mystring operator + (const char *str)//重載了一個+號操作符

??? {

???????strcat(s, str);

???????return *this;

??? }

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??? void operator +=(const char *str)//

??? {

???????strcat(this->s, str);

??? }

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??? mystring operator + (int i)//重載了一個+號操作符,一元操作符重載

??? {

???????char temp[100] = {0};

???????sprintf(temp, "%d", i);

???????strcat(s, temp);

???????return *this;

??? }

??? void operator <<(const char *str)//把<<操作符定義為賦值

??? {

???????strcpy(s, str);

??? }

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??? void operator >>(char *str)//把<<操作符定義為賦值

??? {

???????strcpy(str, s);

??? }

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??? mystring operator ++(int)//重載++操作符的函數int參數是固定

??? {

???????int len = strlen(s);

???????for(int i = 0;i < len; i++)

???????{

???????????s[i]++;//讓s的第一個成員char + 1,就是將s[0]對應字符的ASCII碼 + 1

???????}

???????return *this;

??? }

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??? void * operator new(size_t size)//如果重載的new，那么必須重載delete

??? {

???????//參數size就是sizeof(mystring)的大小.

???????cout << "size = " << size << endl;

???????mystring *p = (mystring *)malloc(size);

???????return p;

??? }

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??? void * operator new[](size_t size)//如果重載的new，那么必須重載delete

??? {

???????//參數size就是sizeof(mystring)的大小 * new[x] + 4個字節.

???????cout << "size = " << size << endl;

???????//mystring *p = (mystring *)malloc(size);

???????return NULL;

??? }

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??? void operator delete[](void *obj)

??? {

???????free((mystring *)obj);

???????obj = NULL;

??? }

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??? void operator delete(void *obj)

??? {

???????free((mystring *)obj);//不能直接free一個void *；

???????obj = NULL;//防止野指針

??? }

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??? bool operator ==(const mystring &it)

??? {

???????if (strcmp(s, it.s) == 0)//如果this->s和it的s相同,就返回true

???????{

???????????return true;

???????}else

???????????return false;

??? }

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??? bool operator ==(const char *str)

??? {

???????if (strcmp(s, str) == 0)//如果this->s和it的s相同,就返回true

???????{

???????????return true;

???????}else

???????????return false;

??? }

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??? //如果返回的是char，代表的是一個右值，右值是不能直接賦值的，

??? //如果返回的是char的引用，那么[]就可以當左值使用了

??? char &operator[](int index)

??? {

???????return s[index];

??? }

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??? void operator ()(const char *str)//重載函數調用操作符

??? {

???????strcpy(s, str);

??? }

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??? void operator ()(int i)

??? {

???????sprintf(s, "%d", i);

??? }

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??? operator int()

??? {

???????return atoi(s);

??? }

?

??? friend mystring operator +(const char *str, const mystring &it);

?

};

?

bool operator ==(const char *str, const mystring &it)

{

??? if (strcmp(str, it.s) == 0)

??? {

???????return true;

??? }else

???????return false;

}

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//操作符重載，有一個最基本條件，就是一定有一個一元是一個自定義的C++類

//如果兩個都是基本數據類型操作符重載是非法的

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mystring operator +(const char *str, const mystring &it)

{

??? mystring str1;

??? char buf[1024] = {0};

??? sprintf(buf, "%s%s", str, it.s);

??? strcpy(str1.s, buf);

??? return str1;

}

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mystring operator ++(mystring &it)

{

??? int len = strlen(it.s);

??? for(int i = 0;i < len; i++)

??? {

???????it.s[i]++;//讓s的第一個成員char + 1,就是將s[0]對應字符的ASCII碼 + 1

??? }

??? return it;

}

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mystring operator +(int i, const mystring &it)

{

??? mystring str1;

??? char buf[1024] = {0};

??? sprintf(buf, "%d%s", i, it.s);

??? strcpy(str1.s, buf);

??? return str1;

}

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class demo

{

public:

??? demo()

??? {

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??? }

};

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void test(int i)

{

??? cout << i << endl;

}

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int main()

{

//??? mystring str;

//??? str << "123";

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//??? test(str);//導致C++編譯器自動的配備int（）操作符

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??? mystring *p = new mystring;

??? delete p;

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//??? mystring *p = (mystring *)malloc(sizeof(mystring));

//??? free(p);

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??? return 0;

}

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int main04()

{

??? mystring str1;

??? str1 << "hello";

??? mystring str2;

??? str2 << "hello";

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??? if ("hello" == str1)

??? {

???????cout << "true" << endl;

??? }else

??? {

???????cout << "fasle" << endl;

??? }

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??? str1[2] = 'a';

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??? //str1("aaaaaaaa");

??? str1(10);

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??? cout << str1.s << endl;

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?

?

?

??? return 0;

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}

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int main03()

{

??? cout << "mystring size =" << sizeof(mystring) << endl;

??? mystring str1;

??? str1 =? "hello";

??? mystring str2;

??? str2 = " world";

??? mystring str3;

??? //str3 = str1 + str2;//對C++編譯器來講，不能識別兩個類+是什么含義

??? //str3 = str1 + "aaaaaaaaaaaa";

??? //str3 = str1 + 100;

??? //str3 = "AAAAA" + str1;

??? str3 = 100 + str1;

??? str3 += "BBBBBB";

??? str3 << "CCCCC";

??? char buf[1024] = {0};

??? str3 >> buf;

??? str2 = str3++;

??? str2 = ++str3;

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??? mystring *pstr = new mystring;

??? delete pstr;

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??? cout << str3.s << endl;

??? return 0;

}

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int main01()

{

??? mystring str1;

??? strcpy(str1.s, "hello world");

??? mystring str2;

??? str2 = str1;//這個過程不是拷貝構造的過程，只是=號操作

??? //str2.operator =(str1);//和直接寫=號是一摸一樣的

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??? cout << str2.s << endl;

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??? str2 = "test";//C++編譯器不能理解把一個字符串賦給一個類是什么含義

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??? mystring str3;

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??? str3 = str2 = 100;

??? //str3 = str2.operator =(100);//上一條語句的等效語法

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??? cout << str2.s << endl;

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??? return 0;

}

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