C++运算符重载

包括：++运算符、+运算符、赋值运算符=、转换运算符、int() char*()运算符、==运算符。

1.重载++运算符

class TestSample{public:TestSample(){};~TestSample(){};void SetNum(int iNum){num = iNum;}int GetNum() const{return num;}const TestSample& operator ++ ()//前缀{++num;return *this;}const TestSample& operator ++ (int)//后缀 注意： int根本没有使用，只是区分前缀后缀{TestSample testSample(*this);++num;return  testSample;}private:int num = 5;};int _tmain(int argc, _TCHAR* argv[]){TestSample testSimpleOne;cout << "testSimpleOne:" << testSimpleOne.GetNum() << endl;//++testSimpleOne;TestSample testSimpleTwo;testSimpleOne++;testSimpleTwo = testSimpleOne++;cout << "testSimpleOne:" << testSimpleOne.GetNum() << endl;cout << "testSimpleTwo:" << testSimpleTwo.GetNum() << endl;testSimpleTwo = ++testSimpleOne;cout << "testSimpleOne:" << testSimpleOne.GetNum() << endl;cout << "testSimpleTwo:" << testSimpleTwo.GetNum() << endl;}

输出：

testSimpleOne:5testSimpleOne:7testSimpleTwo:6testSimpleOne:8testSimpleTwo:8请按任意键继续. . .

2.重载+运算符

class TestSample{public:TestSample(int num){this->num = num;};TestSample(){};~TestSample(){};void SetNum(int iNum){num = iNum;}int GetNum() const{return num;}const TestSample& operator + (const TestSample& obj){return TestSample(num + obj.GetNum());}private:int num = 0;};int _tmain(int argc, _TCHAR* argv[]){TestSample sampleOne(23), sampleTwo(17), sampleThree;sampleThree = sampleOne + sampleTwo;cout << "sampleThree = sampleOne + sampleTwo:" << sampleThree.GetNum() << endl;}

输出：

sampleThree = sampleOne + sampleTwo:40请按任意键继续. . .

3.重载=运算符

C++提供默认的构造函数、析构函数和拷贝构造函数，还有第四个由编译器提供的成员函数：赋值运算符（=）

TestSample sampleOne(23), sampleTwo(17);sampleOne = sampleTwo;cout << "sampleOne:" << sampleOne.GetNum() << endl;

默认的赋值运算符将sampleTwo赋值给sampleOne，sampleOne的num也由23变为17了。

大部分情况下默认的赋值运算符能够对付，与默认拷贝构造函数一样（浅复制，深复制区别），当类中有堆内存成员变量时，导致两个对象指向同一个内存区域，释放内存时会出错，默认函数会造成错误。

class TestSample{public:TestSample(){pStr = new char[200];strncpy_s(pStr, 200, "123456asdf", 10);};~TestSample(){if (pStr){delete[] pStr;pStr = nullptr;}};void SetStr(char* iStr){strncpy_s(pStr, 200, iStr, strlen(iStr));}char* GetString() const{return pStr;}const TestSample& operator = (const TestSample& obj){if (this == &obj) //防止obj = obj的错误情况return *this;if (pStr)//释放*this已经在构造函数中分配的内存，避免内存泄露，无法释放，浪费内存空间{delete[] pStr;pStr = nullptr;}pStr = new char[200];//重新分配内存strncpy_s(pStr, 200, obj.pStr, strlen(obj.pStr));return *this;}private:char* pStr = nullptr;};int _tmain(int argc, _TCHAR* argv[]){TestSample sampleOne, sampleTwo;sampleOne.SetStr("sampleOne!");sampleTwo = sampleOne;cout << "sampleTwo:" << sampleTwo.GetString() << endl;}

输出：

sampleTwo:sampleOne!请按任意键继续. . .

4.转换运算符

如何将一个内置类型值赋值给用户自定义的类对象？比如：将int赋值给类对象。

下面就实践转换运算符，它是一个构造函数的重载版本。

class TestSample{public:TestSample(){};TestSample(int newValue)//转换运算符，它是一个构造函数的重载版本{num = newValue;};~TestSample(){};void SetNum(int num){this->num = num;}int GetNum(){return this->num;}private:int num = 0;};int _tmain(int argc, _TCHAR* argv[]){TestSample sample;int beta = 12;sample = beta;cout <<"sample.GetNum() :" <<sample.GetNum() << endl;}

输出：

sample.GetNum() :12请按任意键继续. . .

5.int() char*()运算符

如何逆向4中讲到的呢，将用户自定义类对象赋值给int,char*?

class TestSample{public:TestSample(){};~TestSample(){};operator unsigned int()//int()运算符{return num;}operator char*()//char*()运算符{return pstr;}void SetNum(int num){this->num = num;}int GetNum(){return this->num;}private:int num = 0;char* pstr = "123afg";};int _tmain(int argc, _TCHAR* argv[]){TestSample sample;sample.SetNum(15);int alpha =  sample;char* beta = sample;cout << "int alpha:" << alpha << endl;cout << "char* beta:" << beta << endl;}

输出：

int alpha:15char* beta:123afg请按任意键继续. . .

6.重载==运算符

如何比较两个对象是否相等？

class TestSample{public:TestSample(){};TestSample(int num){this->num = num;};~TestSample(){};bool operator == (const TestSample& obj){return (this->GetNum() == obj.GetNum()) ? true : false;}void SetNum(int num){this->num = num;}int GetNum() const{return this->num;}private:int num = 0;};int _tmain(int argc, _TCHAR* argv[]){TestSample sampleone(23), sampletwo(23);if (sampleone == sampletwo)//相等cout << "sampletwo is equal to sampleone!" << endl;sampleone.SetNum(21);if (!(sampleone == sampletwo))//不等cout << "sampletwo is not equal to sampleone!" << endl;}

输出：

sampletwo is equal to sampleone!sampletwo is not equal to sampleone!请按任意键继续. . .