question1 赋值运算操作符

Posted 2020-10-08 Emma_U

注意的问题书上讲的很详细了

下面是代码实现，但是VS有一个问题，strcpy安全性较低，虽然可以通脱编译，但是运行会报错，提示用strcpy_s()替代，但是，这里用strcpy()替代也不行，

  1 //题目：如下为类型CMyString的声明，请为该类型添加赋值运算符
  2 //以下为完整代码和测试用例
  3 #pragma warning(disable:4996)
  4 #include <iostream>
  5 #include <cstring>
  6 using namespace std;
  7 class CMyString {
  8 public:
  9     CMyString(char* pData = nullptr);
 10     CMyString(const CMyString& str);
 11     ~CMyString(void);
 12     // operator "="
 13     CMyString& operator =(const CMyString& str);
 14     void print();//用来输出测试结果
 15 private:
 16     char*m_pData;
 17 };
 18 
 19 //the defination of the constructor fun
 20 CMyString::CMyString(char* pData)
 21 {
 22     if (pData == nullptr)
 23         m_pData = new char[1];
 24     m_pData[0] = ‘\0‘;
 25 }
 26 
 27 CMyString::CMyString(const CMyString& str)
 28 {
 29     int len = strlen(str.m_pData);
 30     m_pData = new char[len + 1];
 31     //m_pData(str.m_pData);
 32     strcpy(m_pData, str.m_pData);
 33     
 34 }
 35 
 36 CMyString::~CMyString()
 37 {
 38     //delete m_pData[];
 39     delete[]m_pData;
 40 }
 41 
 42 CMyString& CMyString:: operator =(const CMyString &str)
 43 {
 44     if (this == &str);
 45     return *this;
 46     
 47     delete[]m_pData;
 48     m_pData = nullptr;
 49 
 50     m_pData = new char[strlen(str.m_pData) + 1];
 51     strcpy(m_pData, str.m_pData);
 52     return *this;
 53     
 54 }
 55 
 56 void CMyString:: print()
 57 {
 58     cout << m_pData << endl;
 59 }
 60 //测试用例
 61 
 62 void test1()
 63 {
 64     char* str = "Hello World!";
 65     CMyString str1(str);
 66     CMyString str2;
 67     str2 = str1;//call CMystring& operator=(const CMyString& str)
 68     cout << " str is : " << str << endl;
 69     //cout << "str2 is : " << str2.print() << endl;//没有重载<<运算符，还不能用
 70     cout << "after 赋值" <<"str2 is : "<< endl;
 71     str2.print();
 72  }
 73 
 74 void test2()//赋值给自己
 75 {
 76     char* str = "Hello world!";
 77     CMyString str1(str);
 78     str1=str1;
 79     cout << " str is : " << str << endl;
 80     
 81     cout << "after 赋值" << "str1 is : " << endl;
 82     str1.print();
 83 
 84 }
 85 
 86 void test3()//连续赋值
 87 {
 88     char* str = "Hello World!";
 89     CMyString str1(str);
 90     CMyString str2, str3;
 91     str3 = str2 = str1;
 92     cout << "str1 is : " << endl;
 93     str1.print();
 94     cout << "str2 is : " << endl;
 95 
 96     str2.print();
 97     cout << "str3 is : " << endl;
 98     str3.print();
 99 }
100 
101 
102 int main()
103 {
104     test1();
105     test2();
106     test3();
107     system("pause");
108     return 0;
109 }