C++实现String类

  1 #include<iostream>
  2 #include<cstring>
  3 
  4 class String
  5 {
  6     public:
  7         String();
  8         String(const char *str);
  9         String(const String &rhs);
 10         ~String();
 11 
 12         String &operator=(const String &rhs);
 13         String operator+(const String &rhs);
 14         char operator[](const unsigned int index);
 15         bool operator==(const String &rhs);
 16         friend std::ostream &operator<<(std::ostream &out, const String &rhs);
 17     private:
 18         char *m_data;
 19 };
 20 
 21 String::String()
 22 {
 23     std::cout << "default constructor" << std::endl;
 24     m_data = new char[1];
 25     m_data[0] = '\0';
 26 }
 27 
 28 String::String(const char *str)
 29 {
 30     std::cout << "non-default constructor" << std::endl;
 31     if (NULL == str)
 32     {
 33         m_data = new char[1];
 34         m_data[0] = '\0';
 35     }
 36     else
 37     {
 38         m_data = new char[strlen(str)+1];
 39         strcpy(m_data, str);
 40     }
 41 }
 42 
 43 String::String(const String &another)
 44 {
 45     std::cout << "copy constructor" << std::endl;
 46     m_data = new char[strlen(another.m_data)+1];
 47     strcpy(m_data, another.m_data);
 48 }
 49 
 50 bool String::operator==(const String &rhs)
 51 {
 52     std::cout << "bool == " << std::endl;
 53     int result = strcmp(m_data, rhs.m_data);
 54     if (0 == result)
 55         return true;
 56     else
 57         return false;
 58 }
 59 
 60 String &String::operator=(const String &rhs)
 61 {
 62     std::cout << "assign constructor" << std::endl;
 63     if (this == &rhs)
 64         return *this;
 65     delete []m_data;
 66     m_data = new char[strlen(rhs.m_data)+1];
 67     strcpy(m_data, rhs.m_data);
 68     return *this;
 69 }
 70 
 71 String String::operator+(const String &rhs)
 72 {
 73     std::cout << "+" << std::endl;
 74     String newString;
 75     if (NULL == rhs.m_data)
 76         newString = *this;
 77     else if(NULL == m_data)
 78         newString = rhs;
 79     else
 80     {
 81         newString.m_data = new char[strlen(rhs.m_data)+strlen(m_data)+1];
 82         strcpy(newString.m_data, m_data);
 83         strcat(newString.m_data, rhs.m_data);
 84     }
 85     return newString;
 86 }
 87 
 88 char String::operator[](const unsigned int index)
 89 {
 90     std::cout << "[]" << std::endl;
 91     return m_data[index];
 92 }
 93 
 94 std::ostream &operator<<(std::ostream &out, const String &rhs)
 95 {
 96     out << rhs.m_data;
 97     return out;
 98 }
 99 
100 String::~String()
101 {
102     std::cout << "destructor" << std::endl;
103     delete []m_data;
104 }
105 
106 int main(void)
107 {
108     const char *p = "hello, world";
109     String s = "hello, world"; // 构造函数隐式转换 调用非默认构造函数
110     String s1(p); // 调用非默认构造函数
111     String s2 = s1; // 调用非默认构造函数
112     String s3; // 调用默认构造函数
113     s3 = s1; // 调用赋值构造函数
114     String s4 = s3 + s1; // 调用+运算符，同时调用默认构造函数
115     bool flag(s1 == s2); // 调用==运算符
116     std::cout << s << std::endl;
117     std::cout << s1 << std::endl;
118     std::cout << s2 << std::endl;
119     std::cout << s3 << std::endl;
120     std::cout << flag << std::endl;
121     char result = s3[1]; // 调用[]运算符
122     std::cout << result << std::endl;
123     std::cout << s4 << std::endl;
124 
125     return 0;
126 }