C++如何实现操作符重载

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在C++中经常会遇到重载运算符的问题，其实运算符重载必须将运算符看做
一个函数，分清他的形参返回值，必须搞清楚内存在哪里如何分配如何回收
什么时候生成匿名对象，什么时候使用this指针返回。
运算符可以用友元函数和成员函数完成，一般来讲都使用成员函数，但是某些
特殊的情况必须使用友元函数，比如<< 因为其左操作数为ostream&类型，是不
可能进行任何修改的。

成员函数运算符重载大体步骤如下：

比如Tclass a
    Tclass b
我们要重载=号
    a = b
1、将需要重载的运算符看做一个函数生成operator函数名
如重载等待=
即operator=
2、分清楚形参
   如果是等号重载很明显如果是成员函数形参是右操作数b原型为及
   Tclass& b
   这个时候第一操作数被隐藏即 *this。
3、分清返回值
为了实现如：a=b=c的级联编程，因为=连接性右到左
则为
a=(b=c)即 a.operator=(b.operator=(c))
那么b=c需要返回一个Tclass&类型，当然最好就是 b直接返回
也就是*this内存空间。
那么分析到这里我们可以写出函数原型和返回如下：


Tclass& operator=( Tclass& b)
{
...........
return *this;
}
具体实现具体分析。


下面是一个关于char*类型类的运算符重载，包括了
1、=操作符重载(深拷贝)
2、+操作符重载
3、前置++ 后置++重载
4、!= ==重载
5、<< 重载
因为涉及到char*类型的类容易引起内存泄露下面是测试程序内存泄露检查
==5613== HEAP SUMMARY:
==5613==     in use at exit: 0 bytes in 0 blocks
==5613==   total heap usage: 9 allocs, 9 frees, 102 bytes allocated
==5613== 
==5613== All heap blocks were freed -- no leaks are possible
==5613== 
==5613== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)
==5613== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)


具体代码如下：

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1. 
   

3. #include<iOStream>
   

4. #include<stdlib.h>
   

5. #include<string.h>
   

7. using namespace std;
   

10. class testop
    

11. {
    

12.         private:
    

13.                 char* mystr;
    

14.                 int len;
    

15.         public:
    

16.                 testop(const char* instr)
    

17.                 {
    

18.                         this->len = strlen(instr)+1;
    

19.                         this->mystr = new char[this->len];
    

20.                         memset(this->mystr,0,this->len);
    

21.                         strcpy(this->mystr,instr);
    

22.                 }
    

23.                 testop()
    

24.                 {
    

25.                         this->len = 0;
    

26.                         this->mystr = NULL;
    

27.                 }
    

28.                 testop(const testop& b)//copy 构造函数深拷贝
    

29.                 {
    

30.                         this->len = b.len;
    

31.                         this->mystr = new char[b.len];
    

32.                         memset(this->mystr,0,this->len);
    

33.                         strcpy(this->mystr,b.mystr);
    

34.                 }
    

35.                 void printmystr()
    

36.                 {
    

37.                         cout<<this->mystr<<endl;
    

38.                 }
    

40.                 ~testop()
    

41.                 {
    

42.                         delete [] this->mystr;
    

43.                 }
    

44.                 //操作符重载 + 使用成员函数
    

45.                 testop operator+(const testop& b)
    

46.                 {
    

47.                         testop temp;
    

48.                         temp.len = this->len + b.len;
    

49.                         temp.mystr = new char[temp.len];
    

50.                         memset(temp.mystr,0,temp.len);
    

51.                         strcat(strcat(temp.mystr,this->mystr),b.mystr);
    

52.                         return temp;
    

53.                 }
    

54.                 //操作符重载 = 使用成员函数 深拷贝
    

55.                 testop& operator=(const testop& b)
    

56.                 {
    

57.                         if(this->mystr != NULL)//必须先释放内存
    

58.                         {
    

59.                                 delete [] this->mystr;
    

60.                         }
    

61.                         this->len = b.len;
    

62.                         this->mystr = new char[this->len];
    

63.                         memset(this->mystr,0,this->len);
    

64.                         strcpy(this->mystr,b.mystr);
    

65.                         return *this;
    

66.                 }
    

67.                 //操作符重载前置(++),使用成员函数 支持链试编程
    

69.                 testop& operator++()
    

70.                 {
    

71.                          this->len = this->len+this->len;
    

72.                          char* temp = new char[this->len];
    

73.                          memset(temp,0,this->len);
    

74.                          strcat(strcat(temp,this->mystr),this->mystr);
    

75.                          delete [] this->mystr;
    

76.                          this->mystr = new char[this->len];
    

77.                          strcpy(this->mystr,temp);
    

78.                          delete [] temp;
    

79.                          return *this;
    

80.                 }
    

82.                 //操作符重载后置(++),使用成员函数 不支持链试编程 因为返回的为一个匿名对象
    

84.                 testop operator++(int)
    

85.                 {
    

86.                     testop tempop = *this;
    

87.                         this->len = this->len+this->len;
    

88.                         char* temp = new char[this->len];
    

89.                         memset(temp,0,this->len);
    

90.                         strcat(strcat(temp,this->mystr),this->mystr);
    

91.                         delete [] this->mystr;
    

92.                         this->mystr = new char[this->len];
    

93.                         strcpy(this->mystr,temp);
    

94.                         delete [] temp;
    

95.                         return tempop;
    

96.                 }
    

99.                 //操作符重载 << 必须使用友元函数 支持链试编程
    

100.                 friend ostream& operator<<(ostream& out,testop& b);
     

101.                 //操作符重载 == 使用成员函数
     

102.                 bool operator==(testop& b)
     

103.                 {
     

104.                         if(this->len == b.len && !strcmp(this->mystr,b.mystr))
     

105.                         {
     

106.                                 return true;
     

107.                         }
     

108.                         else
     

109.                         {
     

110.                                 return false;
     

111.                         }
     

112.                 }
     

113.                 //操作符重载 != 使用成员函数
     

114.                 bool operator!=(testop& b)
     

115.                 {
     

116.                         if((*this) == b )
     

117.                         {
     

118.                                 return false;
     

119.                         }
     

120.                         else
     

121.                         {
     

122.                                 return true;
     

123.                         }
     

124.                 }
     

126. };
     

128. ostream& operator<<(ostream& out,testop& b) // 友元函数
     

129. {
     

130.         out<<b.mystr;
     

131.         return out;
     

132. }
     

137. int main()
     

138. {
     

139.         testop c("ab");
     

140.         cout<<c<<endl;
     

141.         c++;
     

142.         ++c;
     

143.         cout<<"c:"<<c<<endl;
     

144.         testop a=c;
     

145.         cout<<"a:"<<a<<endl;
     

146.         if(a == c)
     

147.         {
     

148.                 cout<<"相等"<<endl;
     

149.         }
     

150.         a = c+a;
     

151.         cout<<"a=c+a:"<<a<<endl;
     

152.         if(a !=c )
     

153.         {
     

154.                 cout<<"不相等"<<endl;
     

155.         }
     

157. }

结果如下：
gaopeng@boGon:~/cplusnew/操作符重载$ ./a.out 
ab
c:abababab
a:abababab
相等
a=c+a:abababababababab
不相等

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