• string cow方法实现

    1. #include 
    2. #include 
    3.  
    4. using std::cout;
    5. using std::endl;
    6.  
    7. class String
    8. {
    9. public:
    10.     //String s1;
    11.     String()
    12.     : _pstr(new char[5]() + 4)//1 '\0'   2-5 RefCount  int
    13.     {
    14.         cout << "String()" << endl;
    15.         initRefCount();
    16.     }
    17.  
    18.     //String s1("hello");
    19.     String(const char *pstr)
    20.     : _pstr(new char[strlen(pstr) + 5]() + 4)
    21.     {
    22.         cout << "String(const char *)" << endl;
    23.         strcpy(_pstr, pstr);
    24.         initRefCount();
    25.     }
    26.     //String s2(s1);
    27.     String(const String &rhs)
    28.     : _pstr(rhs._pstr)//浅拷贝
    29.     {
    30.         cout << "String(const String &)" << endl;
    31.         increaseRefCount();
    32.     }
    33.  
    34.     //String s3("world");
    35.     //s3 = s1
    36.     String &operator=(const String &rhs)
    37.     {
    38.         if(this != &rhs)//1、自复制
    39.         {
    40.             //2、释放左操作
    41.             release();
    42.  
    43.             //3、深拷贝(浅拷贝)
    44.             _pstr = rhs._pstr;
    45.             increaseRefCount();
    46.         }
    47.         return *this;//4、返回*this
    48.     }
    49. private:
    50.     class CharProxy
    51.     {
    52.     public:
    53.         CharProxy(String &self, size_t idx)
    54.         : _self(self)
    55.         , _idx(idx)
    56.         {
    57.  
    58.         }
    59.         char &operator=(const char &ch);//写操作
    60.         friend std::ostream &operator<<(std::ostream &os, const CharProxy &rhs);
    61.     private:
    62.         String &_self;//此时String是不完整类型
    63.         size_t _idx;
    64.     };
    65. public:
    66.     //下边访问运算符
    67.     //s3[0] = 'H'
    68.     //cout <<"s1[0] = " << s1[0] << endl;
    69.     CharProxy operator[](size_t idx)//String *this
    70.     {
    71.         return CharProxy(*this, idx);
    72.     }
    73. #if 0
    74.     char &operator[](size_t idx)
    75.     {
    76.         if(idx < this->size())
    77.         {
    78.             if(getRefCount() > 1)//考虑共享问题
    79.             {
    80.                 char *ptmp = new char[size() + 5]() + 4;
    81.                 strcpy(ptmp, _pstr);
    82.                 decreaseRefCount();
    83.  
    84.                 _pstr = ptmp;
    85.                 initRefCount();
    86.             }
    87.             return _pstr[idx];
    88.         }
    89.         else
    90.         {
    91.             static char charnull = '\0';
    92.             return charnull;
    93.         }
    94.     }
    95. #endif
    96.     //s3
    97.     ~String()
    98.     {
    99.         cout << "~String()" << endl;
    100.         release();
    101.     }
    102.  
    103. public:
    104.     const char *c_str() const
    105.     {
    106.         return _pstr;
    107.     }
    108.  
    109.     int getRefCount() const
    110.     {
    111.         return *(int *)(_pstr - 4);
    112.     }
    113.  
    114. private:
    115.     size_t size() const
    116.     {
    117.         return strlen(_pstr);
    118.     }
    119.  
    120.     void initRefCount()
    121.     {
    122.         *(int *)(_pstr - 4) = 1;
    123.     }
    124.  
    125.     void increaseRefCount()
    126.     {
    127.         ++*(int *)(_pstr - 4);
    128.     }
    129.  
    130.     void decreaseRefCount()
    131.     {
    132.         --*(int *)(_pstr - 4);
    133.     }
    134.  
    135.     void release()
    136.     {
    137.         decreaseRefCount();
    138.         if(0 == getRefCount())
    139.         {
    140.             delete [] (_pstr - 4);
    141.         }
    142.     }
    143.  
    144.     friend std::ostream &operator<<(std::ostream &os, const String &rhs);
    145.     friend std::ostream &operator<<(std::ostream &os, const String::CharProxy &rhs);
    146. private:
    147.     char *_pstr;
    148. };
    149.  
    150. std::ostream &operator<<(std::ostream &os, const String &rhs)
    151. {
    152.     if(rhs._pstr)
    153.     {
    154.         os << rhs._pstr;
    155.     }
    156.  
    157.     return os;
    158. }
    159.  
    160. //CharProxy里面的函数
    161. //s3[0] = 'H'
    162. char &String::CharProxy::operator=(const char &ch)
    163. {
    164.     if(_idx < _self.size())
    165.     {
    166.         if(_self.getRefCount() > 1)//考虑共享问题
    167.         {
    168.             char *ptmp = new char[_self.size() + 5]() + 4;
    169.             strcpy(ptmp, _self._pstr);
    170.             _self.decreaseRefCount();
    171.  
    172.             _self._pstr = ptmp;
    173.             _self.initRefCount();
    174.         }
    175.         _self._pstr[_idx] = ch;//真正的赋值操作
    176.  
    177.         return _self._pstr[_idx];
    178.     }
    179.     else
    180.     {
    181.         static char charnull = '\0';
    182.         return charnull;
    183.     }
    184.  
    185. }
    186.  
    187. //双友元的设置
    188. std::ostream &operator<<(std::ostream &os, const String::CharProxy &rhs)
    189. {
    190.     os << rhs._self._pstr[rhs._idx];
    191.  
    192.     return os;
    193. }
    194. void test()
    195. {
    196.     String s1("hello");
    197.     String s2(s1);
    198.     cout << "s1 = " << s1 << endl;
    199.     cout << "s2 = " << s2 << endl;
    200.     cout << "s1.getRefCount() = " << s1.getRefCount() << endl;
    201.     cout << "s2.getRefCount() = " << s2.getRefCount() << endl;
    202.     printf("s1'address : %p\n", s1.c_str());
    203.     printf("s2'address : %p\n", s2.c_str());
    204.  
    205.     cout << endl;
    206.     String s3("world");
    207.     cout << "s3 = " << s3 << endl;
    208.     cout << "s3.getRefCount() = " << s3.getRefCount() << endl;
    209.     printf("s3'address : %p\n", s3.c_str());
    210.  
    211.     cout << endl << "使用s3 = s1进行赋值操作"  << endl;
    212.     s3 = s1;
    213.     cout << "s1 = " << s1 << endl;
    214.     cout << "s2 = " << s2 << endl;
    215.     cout << "s3 = " << s3 << endl;
    216.     cout << "s1.getRefCount() = " << s1.getRefCount() << endl;
    217.     cout << "s2.getRefCount() = " << s2.getRefCount() << endl;
    218.     cout << "s3.getRefCount() = " << s3.getRefCount() << endl;
    219.     printf("s1'address : %p\n", s1.c_str());
    220.     printf("s2'address : %p\n", s2.c_str());
    221.     printf("s3'address : %p\n", s3.c_str());
    222.  
    223.     cout << endl << "对s3[0]执行写操作" << endl;
    224.     s3[0] = 'H';//'h' = 'H' char = char// CharProxy = char//"hello"
    225.     s3.operator[](0).operator=('H');
    226.     cout << "s1 = " << s1 << endl;
    227.     cout << "s2 = " << s2 << endl;
    228.     cout << "s3 = " << s3 << endl;
    229.     cout << "s1.getRefCount() = " << s1.getRefCount() << endl;
    230.     cout << "s2.getRefCount() = " << s2.getRefCount() << endl;
    231.     cout << "s3.getRefCount() = " << s3.getRefCount() << endl;
    232.     printf("s1'address : %p\n", s1.c_str());
    233.     printf("s2'address : %p\n", s2.c_str());
    234.     printf("s3'address : %p\n", s3.c_str());
    235.  
    236.     cout << endl << "对s1[0]执行读操作" << endl;
    237.     cout << "s1[0] = " << s1[0] << endl;//cout << CharProxy//CharProxy -> char
    238.     cout << "s1 = " << s1 << endl;
    239.     cout << "s2 = " << s2 << endl;
    240.     cout << "s3 = " << s3 << endl;
    241.     cout << "s1.getRefCount() = " << s1.getRefCount() << endl;
    242.     cout << "s2.getRefCount() = " << s2.getRefCount() << endl;
    243.     cout << "s3.getRefCount() = " << s3.getRefCount() << endl;
    244.     printf("s1'address : %p\n", s1.c_str());
    245.     printf("s2'address : %p\n", s2.c_str());
    246.     printf("s3'address : %p\n", s3.c_str());
    247.  
    248. }
    249. int main(int argc, char **argv)
    250. {
    251.     test();
    252.     return 0;
    253. }
    254.  
    1. #include 
    2. #include 
    3. #include 
    4.  
    5. using std::cout;
    6. using std::endl;
    7. using std::vector;
    8.  
    9. class String 
    10. {
    11. public:
    12.     String()
    13.    // : _pstr(nullptr)//后面操作的时候，需要判空
    14. 	: _pstr(new char[1]())
    15.     {
    16.         cout << "String()" << endl;
    17.     }
    18.  
    19.     //String s1("hello")
    20.     String(const char *pstr)
    21.     : _pstr(new char[strlen(pstr) + 1]())
    22.     {
    23.         cout << "String(const char *)" << endl;
    24.         strcpy(_pstr, pstr);
    25.     }
    26.  
    27.     //String s2(s1);
    28.     String(const String &rhs)
    29.     : _pstr(new char[strlen(rhs._pstr) +1]())
    30.     {
    31.         cout << "String(const String &)" << endl;
    32.         strcpy(_pstr, rhs._pstr);
    33.     }
    34.  
    35.     ~String()
    36.     {
    37.         cout << "~String()" << endl;
    38.         if(_pstr)
    39.         {
    40.             delete [] _pstr;
    41.             _pstr = nullptr;
    42.         }
    43.     }
    44.  
    45.     //String s1;
    46.     //s1 = s1;
    47.     String &operator=(const String &rhs)
    48.     {
    49.         cout << "String &operator=(const String &)" << endl;
    50.         if(this != &rhs)
    51.         {
    52.             delete [] _pstr;
    53.             _pstr = nullptr;
    54.  
    55.             _pstr = new char[strlen(rhs._pstr) + 1]();
    56.             strcpy(_pstr, rhs._pstr);
    57.         }
    58.         return  *this;
    59.     }
    60.  
    61.     // s1 = "hello";
    62.     String &operator=(const char *pstr)
    63.     {
    64.         cout << "String &operator=(const char *)" << endl;
    65.         String tmp(pstr);
    66.         *this = tmp;
    67.  
    68.         return *this;
    69.     }
    70.  
    71.     //s1 += s2;
    72.     String &operator+=(const String &rhs)
    73.     {
    74.         cout << "String &operator+=(const String &)" <
    75.         String tmp;
    76.         if(tmp._pstr)
    77.         {
    78.             delete [] tmp._pstr;//防止内存泄漏
    79.         }
    80.         tmp._pstr = new char[strlen(_pstr) + 1]();
    81.         strcpy(tmp._pstr, _pstr);
    82.         delete [] _pstr;
    83.         _pstr = nullptr;
    84.         _pstr = new char[strlen(rhs._pstr) + strlen(tmp._pstr) + 1]();
    85.         strcpy(_pstr, tmp._pstr);
    86.         strcat(_pstr, rhs._pstr);
    87.  
    88.         return *this;
    89.     }
    90.  
    91.     //s1 += "hello"
    92.     String &operator+=(const char *pstr)
    93.     {
    94.         cout << "String &operator+=(const char *)" << endl;
    95.         String tmp(pstr);
    96.         *this += tmp;
    97.  
    98.         return *this;
    99.     }
    100.  
    101.     //const String s1("helo");
    102.     //s1[0]
    103.     char &operator[](std::size_t index)//index > = 0
    104.     {
    105.         if(index < size())
    106.         {
    107.             return _pstr[index];
    108.         }
    109.         else
    110.         {
    111.             static char nullchar = '\0';
    112.             return nullchar;
    113.         }
    114.     }
    115.  
    116.     const char &operator[](std::size_t index) const
    117.     {
    118.         if(index < size())
    119.         {
    120.             return _pstr[index];
    121.         }
    122.         else
    123.         {
    124.             static char nullchar = '\0';
    125.             return nullchar;
    126.         }
    127.  
    128.     }
    129.  
    130.     std::size_t size() const
    131.     {
    132.         return strlen(_pstr);
    133.     }
    134.  
    135.     const char* c_str() const
    136.     {
    137.         return _pstr;
    138.     }
    139.  
    140.     friend bool operator==(const String &, const String &);
    141.     friend bool operator!=(const String &, const String &);
    142.  
    143.     friend bool operator<(const String &, const String &);
    144.     friend bool operator>(const String &, const String &);
    145.     friend bool operator<=(const String &, const String &);
    146.     friend bool operator>=(const String &, const String &);
    147.  
    148.     friend std::ostream &operator<<(std::ostream &os, const String &s);
    149.     friend std::istream &operator>>(std::istream &is, String &s);
    150.  
    151. private:
    152.     char * _pstr;
    153.  
    154. };
    155.  
    156. bool operator==(const String &lhs, const String &rhs)
    157. {
    158.     return !strcmp(lhs._pstr, rhs._pstr);
    159. }
    160.  
    161. bool operator!=(const String &lhs, const String &rhs)
    162. {
    163.     return strcmp(lhs._pstr, rhs._pstr);
    164. }
    165.  
    166. bool operator<(const String &lhs, const String &rhs)
    167. {
    168.     return strcmp(lhs._pstr, rhs._pstr) < 0;
    169. }
    170.  
    171. bool operator>(const String &lhs, const String &rhs)
    172. {
    173.     return strcmp(lhs._pstr, rhs._pstr) > 0;
    174. }
    175. bool operator<=(const String &lhs, const String &rhs)
    176. {
    177.     return strcmp(lhs._pstr, rhs._pstr) <= 0;
    178. }
    179. bool operator>=(const String &lhs, const String &rhs)
    180. {
    181.     return strcmp(lhs._pstr, rhs._pstr) >= 0;
    182. }
    183.  
    184. std::ostream &operator<<(std::ostream &os, const String &rhs)
    185. {
    186.     if(rhs._pstr)
    187.     {
    188.         os << rhs._pstr;
    189.     }
    190.  
    191.     return os;
    192. }
    193.  
    194. //String s1("hello")
    195. //cin >> s1;
    196. std::istream &operator>>(std::istream &is, String &rhs)
    197. {
    198.     if(rhs._pstr)
    199.     {
    200.         delete [] rhs._pstr;
    201.         rhs._pstr = nullptr;
    202.     }
    203.  
    204.     //动态获取从键盘输入数据的长度
    205.     vector<char> buffer;
    206.     char ch;
    207.     while((ch = is.get()) != '\n')
    208.     {
    209.         buffer.push_back(ch);
    210.     }
    211.  
    212.     rhs._pstr = new char[buffer.size() + 1]();
    213.     strncpy(rhs._pstr, &buffer[0], buffer.size());
    214.  
    215.     return is;
    216. }
    217.  
    218. String operator+(const String &lhs, const String &rhs)
    219. {
    220.     cout << "String operator+(const String &, const String &)" << endl;
    221.  
    222.     String tmp(lhs);
    223.     tmp += rhs;
    224.  
    225.     return tmp;
    226. }
    227. String operator+(const String &lhs, const char *pstr)
    228. {
    229.     cout << "String operator+(const String &, const char *)"<< endl;
    230.     String tmp(lhs);
    231.     tmp += pstr;
    232.  
    233.     return tmp;
    234.  
    235. }
    236. String operator+(const char *pstr, const String &rhs)
    237. {
    238.     cout << "String operator+(const char*, const String &)" << endl;
    239.     String tmp(pstr);
    240.     tmp += rhs;
    241.  
    242.     return tmp;
    243.  
    244. }
    245.  
    246.  
    247. void test()
    248. {
    249.     String s1;
    250.     /* std::cin >> s1; */
    251.     cout << "s1 = " << s1 << endl;
    252.  
    253.     cout << endl << endl;
    254.     String s2 = "hello";
    255.     cout << "s2 = " << s2 << endl;
    256.  
    257.     cout << endl << "1111" <<  endl;
    258.     s2 = "world"; //error
    259.     cout << "s2 = " << s2 << endl;
    260.  
    261.     cout << endl << endl;
    262.     s2 = s2;
    263.     cout << "s2 = " << s2 << endl;
    264.  
    265.     cout << endl << endl;
    266.     String s3 = "wuhan";
    267.     s3 += " welcome to string word";
    268.     cout << "s3 = " << s3 << endl;
    269.  
    270. }
    271. int main(int argc, char **argv)
    272. {
    273.     test();
    274.     return 0;
    275. }
    276.

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  • 原文地址：https://blog.csdn.net/INGNIGHT/article/details/133501336