string类（三）

string类的模拟实现：

1.默认成员变量和函数

首先自定义构造string类的默认成员变量和函数

声明和定义均在头文件（自己创建的string.h）中进行，主函数仅调用函数

#pragma once
#include <iostream>
using namespace std;
#include <string>namespace pzh   //pzh为命名空间名称 
{class string  //pzh::string为自定义的string类的名称{public:string(const char* str = "")  //构造函数   : _size(strlen(str)){_capacity = _size;_str = new char[_capacity + 1];strcpy(_str, str);}~string()  //析构函数{delete[] _str;_str = nullptr;_size = _capacity = 0;}const char* c_str()  //打印字符串函数{return _str;}private:char* _str;size_t _size;size_t _capacity;};void func_str1(){string s1;string s2("hello solity");cout << s1.c_str() << endl;cout << s2.c_str() << endl;}
}

运行结果：

2.string的长度和下表引用

定义size和**[ ]**：

size_t size() const
{return _size;
}char& operator[](size_t pos)
{assert(pos < _size);  //需要引入头文件 #inlcude <assert.h>return _str[pos];
}

测试功能调用：

void func_str()
{string s("hello solity");cout << s.size() << endl;for (size_t i = 0; i < s.size(); ++i){cout << s[i] << " ";}
}

运行结果：

3.字符串拷贝构造

此时如果需要进行字符串复制拷贝，便需要进行构造拷贝函数

string(const string& s)  //拷贝构造: _size(s._size)  //将s的size长度赋值给成员变量_size, _capacity(s._capacity)
{_str = new char[s._capacity + 1];  //加1是给'\0'准备的（深拷贝）strcpy(_str, s._str);
}

调用测试：

void func_str()
{string s1("hello solity");  //sstring s2(s1);  //thiscout << s1.c_str() << endl;cout << s2.c_str() << endl;
}

运行结果：

4. +=赋值拷贝

赋值不止有这种，当然还有**=**号进行赋值拷贝

string& operator=(const string& s)
{if (this != &s){char* tmp = new char[s._capacity + 1];  //先开新空间strcpy(tmp, s._str); //进行拷贝delete[] _str; //释放旧空间(this)_str = tmp;  //把新开空间给旧空间_size = s._size;_capacity = s._capacity;}return *this;
}

测试运行：

void func_str()
{string s1; string s2("hello solity");cout << "Before s1 = " << s1.c_str() << endl;cout << "Before s2 = " << s2.c_str() << endl;s1 = s2;cout << "After s1 = " << s1.c_str() << endl;cout << "After s2 = " << s2.c_str() << endl;
}

输出结果：

5.字符串比较

当需要进行字符串比较的操作时：

bool operator>(const string& s) const
{return strcmp(_str, s._str) > 0;
}bool operator==(const string& s) const
{return strcmp(_str, s._str) == 0;
}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 !(*this > s);
}bool operator!=(const string& s) const
{return !(*this == s);
}

测试运行：

void func_str()
{string s1("hello solity");string s2("hello pzh");string s3("abc");cout << (s1 < s2) << endl;cout << (s1 == s2) << endl;cout << (s1 >= s2) << endl; 
}

输出结果：

6.字符串的增添操作

void reserve(size_t n)
{char* tmp = new char[n + 1];strcpy(tmp, _str);delete[] _str;_str = tmp;_capacity = n;
}void push_back(char ch)  //添加字符
{if (_size + 1 > _capacity){reserve(_capacity * 2);}_str[_size] = ch;++_size;_str[_size] = '\0';
}void append(const char* str)  //添加字符串
{size_t len = strlen(str);if (_size + len > _capacity){reserve(len + _size);}strcpy(_str + _size, str);_size += len;
}

测试运行：

void func_str()
{string s1("hello solity");s1.push_back(' ');cout << s1.c_str() << endl;s1.append("#####################");cout << s1.c_str() << endl;;
}

输出结果：

当然，追加操作这样就显得很臃肿，我们可以尝试更简介的**+=**操作符来进行:

string& operator+=(const char* str)
{append(str);return *this;
}

测试运行：

void func_str()
{string s1("hello solity");s1.push_back(' ');cout << s1.c_str() << endl;s1.append("#####################");cout << s1.c_str() << endl;s1 += "pzh solity";cout << s1.c_str() << endl;
}

输出结果：

7.insert插入操作

void insert(size_t pos, char ch)
{assert(pos <= _size);if (_size + 1 > _capacity){reserve(2 * _capacity);}size_t end = _size;while (end >= pos){_str[end + 1] = _str[end];--end;}_str[pos] = ch;++_size;
}

测试运行：

void func_str()
{string s1("hello solity");cout << "Before s1 = " << s1.c_str() << endl;s1.insert(2, 'a');cout << "After s1 = " << s1.c_str() << endl;
}

输出结果：

8.遍历字符

测试运行：

void func_str()
{string s1("hello solity");for (size_t i = 0; i < s1.size(); ++i){cout << s1[i] << " ";  //输出运算后结果}cout << endl;for (size_t i = 0; i < s1.size(); ++i){s1[i]++;  //对每个字符进行加1操作}for (size_t i = 0; i < s1.size(); ++i){cout << s1[i] << " ";  //输出运算后结果}cout << endl;
}

输出结果：

如果使用范围for进行输出，便需要用到迭代器：

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;
}

测试运行：

void func_str()
{string s("hello solity");string::iterator it = s.begin();while (it != s.end()){cout << *it << " ";++it;}cout << endl;for (auto ch : s){cout << ch << " ";}}

输出结果：

iterator end()
{
return _str + _size;
}

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

测试运行：```c++
void func_str()
{string s("hello solity");string::iterator it = s.begin();while (it != s.end()){cout << *it << " ";++it;}cout << endl;for (auto ch : s){cout << ch << " ";}}

输出结果：

综上，完整的string.h头文件如下：

#pragma once
#include <iostream>
using namespace std;
#include <string>
#include <assert.h>namespace pzh  
{class string{public: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;}string(const char* str = "")  //构造函数   : _size(strlen(str)){_capacity = _size;_str = new char[_capacity + 1];strcpy(_str, str);}~string()  //析构函数{delete[] _str;_str = nullptr;_size = _capacity = 0;}const char* c_str()  //打印字符串函数{return _str;}size_t size() const  //字符串长度{return _size;}char& operator[](size_t pos)  //字符串下表引用{assert(pos < _size);return _str[pos];}string(const string& s)  //拷贝构造: _size(s._size)  //将s的size长度赋值给成员变量_size, _capacity(s._capacity){_str = new char[s._capacity + 1];  //加1是给'\0'准备的（深拷贝）strcpy(_str, s._str);}string& operator=(const string& s){if (this != &s){char* tmp = new char[s._capacity + 1];strcpy(tmp, s._str);delete[] _str;  _str = tmp;_size = s._size;_capacity = s._capacity;delete[] tmp;}return *this;}//不修改成员变量的函数，保险起见统统加constbool operator>(const string& s) const{return strcmp(_str, s._str) > 0;}bool operator==(const string& s) const{return strcmp(_str, s._str) == 0;}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 !(*this > s);}bool operator!=(const string& s) const{return !(*this == s);}void reserve(size_t n){char* tmp = new char[n + 1];strcpy(tmp, _str);delete[] _str;_str = tmp;_capacity = n;}void push_back(char ch){if (_size + 1 > _capacity){reserve(_capacity * 2);}_str[_size] = ch;++_size;_str[_size] = '\0';}void append(const char* str){size_t len = strlen(str);if (_size + len > _capacity){reserve(len + _size);}strcpy(_str + _size, str);_size += len;}string& operator+=(const char* str){append(str);return *this;}void insert(size_t pos, char ch){assert(pos <= _size);if (_size + 1 > _capacity){reserve(2 * _capacity);}size_t end = _size;while (end >= pos){_str[end + 1] = _str[end];--end;}_str[pos] = ch;++_size;}private:char* _str;size_t _size;size_t _capacity;};void func_str(){//...测试功能代码}
}

main.cpp主文件如下：

#define _CRT_SECURE_NO_WARNINGS
#include "string.h"int main()
{pzh::func_str();return 0;
}