那些年我与c++的叫板（一）--string类自实现

引子：我们学习了c++中的string类，那我们能不能像以前数据结构一样自己实现string类呢？以下是cplusplus下的string类，我们参考参考！

废话不多说，直接代码实现：（注意函数之间的复用！）

#define _CRT_SECURE_NO_WARNINGS 1
#pragma once
#include<iostream>
#include<assert.h>
using namespace std;
//一般在类外进行静态区变量赋值
const static size_t npos = -1;
//本string简单实现，代码量小，故直接写在声明中
namespace bit
{
   class string
   {
   public:
       //采用typedef 让iterator保持接口的一致性
       //iterator底层是模版template
       typedef char* iterator;
       typedef const char* const_iterator;

       iterator begin()
       {
           return _str;
       }
       iterator end()
       {
           return _str + _size;
       }
       const_iterator begin() const
       {
           return _str;
       }
       const_iterator end() const
       {
           return _str + _size;
       }

       //构造函数
       string(const char* str = "")
           :_size(strlen(str))
       {
           _str = new char[_size + 1];//为深拷贝，因为如果浅拷贝的话，共用一块空间，那结果可想而知
           _capacity = _size;
           strcpy(_str, str);//注意char * strcpy ( char * destination, const char * source );
       }
       //拷贝构造,可以隐式类型赋值
       string(const string& s)
       {
           _str = new char[s._capacity + 1];
           strcpy(_str, s._str);
           _size = s._size;
           _capacity = s._capacity;
       }
       string& operator=(const string& s)
       {
           if (this != &s)//排除等于自身的情况
           {
               char* tmp = new char[s._capacity + 1];
               strcpy(tmp, s._str);
               delete[]_str;//只析构_str上的资源
               _str = tmp;
               _size = s._size;
               _capacity = s._capacity;
           }
           return *this;
       }
       ~string()
       {
           delete[]_str;
           _str = nullptr;
           _size = _capacity = 0;
       }
       const char* c_str() const
       {
           return _str;
       }
       size_t size() const
       {
           return _size;
       }
       char& operator[](size_t pos)
       {
           assert(pos < _size);
           return _str[pos];
       }
       const char& operator[](size_t pos) const
       {
           assert(pos < _size);
           return _str[pos];
       }

       void reserve(size_t n)
       {
           if (n > _capacity)
           {
               char* tmp = new char[n + 1];
               strcpy(tmp, _str);
               delete[] _str;

               _str = tmp;
               _capacity = n;
           }
       }
       void insert(size_t pos, char ch)
       {
           assert(pos <= _size);

           if (_size == _capacity)
           {
               size_t newcapacity = _capacity == 0 ? 4 : _capacity * 2;
               reserve(newcapacity);
           }
           size_t end = _size + 1;
           while (end > pos)
           {
               _str[end] = _str[end - 1];
               --end;
           }
           _str[pos] = ch;
           ++_size;
       }
       void insert(size_t pos, const char* str)
       {
           assert(pos <= _size);
           size_t len = strlen(str);
           if (_size + len > _capacity)
           {
               reserve(_size + len);
           }
           size_t end = _size;
           //注意pos=0时，对应的值为size_t类型，要int转
           while (end > (int)pos)
           {
               _str[end+len] = _str[end];
               --end;
           }

           memcpy(_str + pos, str, len);//void * memcpy ( void * destination, const void * source, size_t num );
           _size += len;
       }
       void push_back(char ch)
       {
           insert(_size, ch);
       }
       void append(const char* str)
       {
           insert(_size, str);
       }
       string& operator+=(char ch)
       {
           push_back(ch);
           return *this;
       }
       string& operator+=(const char* str)
       {
           append(str);
           return *this;
       }
       void erase(size_t pos = 0, size_t len = npos)
       {
           assert(pos < _size);

           // len大于前面字符个数时，有多少删多少
           if (len >= _size - pos)
           {
               _str[pos] = '\0';
               _size = pos;
           }
           else
           {
               strcpy(_str + pos, _str + pos + len);
               _size -= len;
           }
       }

       size_t find(char ch, size_t pos = 0)
       {
           for (size_t i = pos; i < _size; i++)
           {
               if (_str[i] == ch)
               {
                   return i;
               }
           }
           return npos;
       }
       size_t find(const char* str, size_t pos = 0)
       {
           char* p = strstr(_str + pos, str);//char * strstr (char * str1, const char * str2 );
           return p - _str;
       }
       void swap(string& s)
       {
           std::swap(_str, s._str);
           std::swap(_size, s._size);
           std::swap(_capacity, s._capacity);
       }
       string substr(size_t pos = 0, size_t len = npos)
       {
           // len大于后面剩余字符，有多少取多少
           if (len > _size - pos)
           {
               string sub(_str + pos);
               return sub;
           }
           else
           {
               string sub;
               sub.reserve(len);
               for (size_t i = 0; i < len; i++)
               {
                   sub += _str[pos + i];
               }
               return sub;
           }
       }
       bool operator<(const string& s) const
       {
           return strcmp(_str, s._str) < 0;
       }
       bool operator>(const string& s) const
       {
           return !(*this <= s);
       }
       bool operator<=(const string& s) const
       {
           return *this < s || *this == s;
       }
       bool operator>=(const string& s) const
       {
           return !(*this < s);
       }
       bool operator==(const string& s) const
       {
           return strcmp(_str, s._str) == 0;
       }
       bool operator!=(const string& s) const
       {
           return !(*this == s);
       }
       void clear()
       {
           _str[0] = '\0';
           _size = 0;
       }
   private:
       // char _buff[16];
       char* _str;
       size_t _size;
       size_t _capacity;
       const static size_t npos;
   };
   istream& operator>> (istream& is, string& str)
   {
       str.clear();
       char ch = is.get();
       while (ch != ' ' && ch != '\n')
       {
           str += ch;
           ch = is.get();
       }
       return is;
   }
   ostream& operator<< (ostream& os, const string& str)
   {
       for (size_t i = 0; i < str.size(); i++)
       {
           os << str[i];
       }
       return os;
   }
}