重载运算符函数及其注意事项

  1 #include "stdafx.h"
  2 #include <string>
  3 
  4 class CMyString
  5 {
  6 public:
  7     CMyString(char* pData = NULL);
  8     CMyString(const CMyString& str);
  9     ~CMyString(void);
 10 
 11     CMyString& operator = (const CMyString& str);
 12 
 13     void Print();
 14       
 15 private:
 16     char* m_pData;
 17 };
 18 
 19 CMyString::CMyString(char *pData)
 20 {
 21     if(pData == NULL)
 22     {
 23         m_pData = new char[1];
 24         m_pData[0] = '';
 25     }
 26     else
 27     {
 28         int length = strlen(pData);
 29         m_pData = new char[length + 1];
 30         strcpy(m_pData, pData);
 31     }
 32 }
 33 
 34 CMyString::CMyString(const CMyString &str)
 35 {
 36     int length = strlen(str.m_pData);
 37     m_pData = new char[length + 1];
 38     strcpy(m_pData, str.m_pData);
 39 }
 40 
 41 CMyString::~CMyString()
 42 {
 43     delete[] m_pData;
 44 }
 45 
 46 CMyString& CMyString::operator = (const CMyString& str)
 47 {
 48     if(this == &str)
 49         return *this;
 50 
 51     delete []m_pData;
 52     m_pData = NULL;
 53 
 54     m_pData = new char[strlen(str.m_pData) + 1];
 55     strcpy(m_pData, str.m_pData);
 56 
 57     return *this;
 58 }
 59 
 60 // ====================测试代码====================
 61 void CMyString::Print()
 62 {
 63     printf("%s", m_pData);
 64 }
 65 
 66 void Test1()
 67 {
 68     printf("Test1 begins:
");
 69 
 70     char* text = "Hello world";
 71 
 72     CMyString str1(text);
 73     CMyString str2;
 74     str2 = str1;
 75 
 76     printf("The expected result is: %s.
", text);
 77 
 78     printf("The actual result is: ");
 79     str2.Print();
 80     printf(".
");
 81 }
 82 
 83 // 赋值给自己
 84 void Test2()
 85 {
 86     printf("Test2 begins:
");
 87 
 88     char* text = "Hello world";
 89 
 90     CMyString str1(text);
 91     str1 = str1;
 92 
 93     printf("The expected result is: %s.
", text);
 94 
 95     printf("The actual result is: ");
 96     str1.Print();
 97     printf(".
");
 98 }
 99 
100 // 连续赋值
101 void Test3()
102 {
103     printf("Test3 begins:
");
104 
105     char* text = "Hello world";
106 
107     CMyString str1(text);
108     CMyString str2, str3;
109     str3 = str2 = str1;
110 
111     printf("The expected result is: %s.
", text);
112 
113     printf("The actual result is: ");
114     str2.Print();
115     printf(".
");
116 
117     printf("The expected result is: %s.
", text);
118 
119     printf("The actual result is: ");
120     str3.Print();
121     printf(".
");
122 }
123 
124 int _tmain(int argc, _TCHAR* argv[])
125 {
126     Test1();
127     Test2();
128     Test3();
129 
130     return 0;
131 }

剑指offer里面提到，如果让写一个重载运算符函数需要注意的4个事项

1：返回值一定要是引用，也就是自身*this，这样才能保证连续赋值

2:：形参要是引用不能是实例，否则会自身调用复制构造函数，造成浪费，减慢效率，同时为了不修改，应该const 修饰

3：在分配内存之前要释放以前的内存

4：最初一定要判断*this和传入的是否是同一个，如果是同一个，那么直接返回，否则，会delete全部删除