文章目录

• string的介绍
• string的模拟实现
• • string类的成员变量
  • Member functions
  • • constructor（构造函数）
    • destructor（析构函数）
    • operator=(给创建出来的对象赋值)
  • Iterators（迭代器）
  • • begin
    • end
  • Capacity
  • • size
    • capacity
    • reserve
    • resize
    • clear
  • Element access
  • • operator[]
  • Modifiers
  • • operator+=
    • append
    • push_back
    • insert
    • erase
    • swap
  • String operations
  • • c_str
    • find
  • Member constants
  • • npos
  • Non-member function overloads
  • • operator>>
    • operator<<
  • 比较运算符重载
• 完整版string类代码
• • string.h
  • test.cpp

string的介绍

string是C++ STL库中一个重要的容器，它分为以下几个部分（将在vs编译器下实现）
Member function

Iterators

Capacity

Element access

Modifiers

String operations

Member constants

Non-member function overloads

在大家了解了string的每个部分的成员函数之后，我们就要去模拟实现每个部分之中在日常中经常使用到的一些成员函数。

string的模拟实现

string类的成员变量

Member functions

constructor（构造函数）

在这里我们主要实现构造函数常用的三种也就是图中的（1），（2），（4）


其中一写函数的注释代码，是代码优化前的写法，大家可以用来做参考和理解。

destructor（析构函数）

operator=(给创建出来的对象赋值)

在这里我们只实现第一种。

Iterators（迭代器）

在这里我们只实现了正向迭代器

由图片可以看出起始迭代器就只是一个被重新定义的指针。

begin

end

end和begin相似

Capacity

size

capacity

reserve

resize

resize功能和reserve一样但是多了个初始化和缩容

clear

Element access

operator[]

都是返回pos位置的字符

Modifiers

operator+=

这里只实现了（2）和（3）两个版本

append

push_back

insert

在这里指定位置插入函数就实现了2个常用的版本

erase

swap

String operations

c_str

find

Member constants

npos

Non-member function overloads

operator>>

operator<<

比较运算符重载

完整版string类代码

string.h

#pragma once
namespace lzy
{class string{public:typedef char* iterator;typedef const char* const_iterator;iterator begin(){return _str;}const_iterator begin()const{return _str;}iterator end(){return _str + _size;}const_iterator end()const{return _str + _size;}//string sstring():_str(new char[1]), _size(0), _capacity(0){_str[0] = '\0';}//创建一个空类//string("hello world")string(const char* s):_size(strlen(s)), _capacity(_size){_str = new char[_size + 1];strcpy(_str, s);}//用字符串初始化创建一个类//string s1(s2)string(const string& s)//:_size(s._size):_size(0), _capacity(0){/*_str = new char[_size+1];strcpy(_str, s._str);*/string temp(s._str);swap(temp);}//用类初始化创建一个类~string(){delete[] _str;}//s1 = s2 = s3//s1 = s1void swap(string& s){std::swap(_str, s._str);std::swap(_size, s._size);std::swap(_capacity, s._capacity);}//const string& operator=(const string& s)//{//	if (&s != this)//	{//		//重新为数组开辟一块空间，不管空间是否足够//		delete[] _str;//		_str = new char[s._size + 1];//		//开始为这块新开辟的空间赋值//		for (int i = 0; i <= s._size; i++)//		{//			_str[i] = s._str[i];//		}//		_size = s._size;//		_capacity = s._capacity;//	}//	return *this;//}const string& operator=(string s){//if (&s != this)//{//	//重新为数组开辟一块空间，不管空间是否足够//	delete[] _str;//	_str = new char[s._size + 1];//	//开始为这块新开辟的空间赋值//	for (int i = 0; i <= s._size; i++)//	{//		_str[i] = s._str[i];//	}//	_size = s._size;//	_capacity = s._capacity;//}/*swap(_str, s._str);swap(_size, s._size);swap(_str, s._str);*/swap(s);return *this;}const char* c_str() const{return _str;}size_t size()const{return _size;}size_t capacity()const{return _capacity;}//s[i] 可修改char& operator[](size_t pos){//越界访问就报错assert(pos < _size);return *(_str + pos);}//s[i] const对象不可修改const char& operator[](size_t pos)const{// 越界访问就报错assert(pos < _size);return *(_str + pos);}void reserve(size_t n){if (n > _capacity){char* temp = new char[n + 1];strcpy(temp, _str);delete[] _str;_str = temp;_capacity = n;}}void resize(size_t n, char x = '\0'){if (n > _capacity){char* temp = new char[n + 1];memset(temp, x, n + 1);strcpy(temp, _str);delete[] _str;_str = temp;_capacity = n;_size = n;}else{_size = n;_str[_size] = '\0';}}//尾插入一个字符void push_back(char ch){if (_size == _capacity){//增容/*size_t newcapacity = _capacity == 0 ? 4 : _capacity * 2;char* temp= new char[newcapacity+1];strcpy(temp, _str);delete[] _str;_str = temp;_capacity = newcapacity;*/reserve(_capacity == 0 ? 4 : _capacity * 2);}_str[_size] = ch;_size++;_str[_size] = '\0';}//尾插入一段字符串void append(const char* s){size_t length = strlen(s);//判断空间是否足够if (_size + length > _capacity){增容//char* temp = new char[_size + length+1];//strcpy(temp, _str);//delete[] _str;//_str = temp;//_capacity = _size;///*for (int i = 0; i //	_str[i + _size] = s[i];//}*///	//增容reserve(_size + length);//	for (int i = 0; i < length; i++)//	{//		_str[i + _size] = s[i];//	}//	_size += length;//	//}//else//{//	for (int i = 0; i //		_str[i + _size] = s[i];//	}//	_size += length;//	_str[_size] = '\0';}strcpy(_str + _size, s);_size += length;}string& operator+=(char ch){push_back(ch);return *this;}string& operator+=(const char* s){append(s);return *this;}size_t find(char ch) const{for (size_t i = 0; i < _size; i++){if (_str[i] == ch){return i;}}return npos;}size_t find(const char* s, size_t pos = 0){char* temp = strstr(_str + pos, s);if (temp == nullptr){return npos;}return temp - _str;}string& insert(char ch, size_t pos){if (_size == _capacity){//增容/*size_t newcapacity = _capacity == 0 ? 4 : _capacity * 2;char* temp = new char[newcapacity + 1];strcpy(temp, _str);delete[] _str;_str = temp;_capacity = newcapacity;*/reserve(_capacity == 0 ? 4 : _capacity * 2);}size_t end = _size + 1;while (pos < end){_str[end] = _str[end - 1];--end;}_str[pos] = ch;_size++;//_str[_size] = '\0';return *this;}string& insert(const char* s, size_t pos){assert(pos <= _size);size_t len = strlen(s);if (_size + len > _capacity){//增容/*size_t newcapacity = _size + len;char* temp = new char[newcapacity + 1];strcpy(temp, _str);delete[] _str;_str = temp;_capacity = newcapacity;*/reserve(_size + len);}size_t end = _size + len;while (pos + len < end){_str[end] = _str[end - len];--end;}//_str[pos] = ch;strcpy(_str + pos, s);_size += len;return *this;}string& erase(size_t pos, size_t len = npos){assert(pos <= _size);if (len == npos || pos + len > _size){_str[pos] = '\0';_size = pos;}else{//_str[pos] = '\0';strcpy(_str + pos, _str + pos + len);_size -= len;}return *this;}void clear(){_str[0] = '\0';_size = 0;}private:char* _str;size_t _size;size_t _capacity;static size_t npos;};size_t string::npos = -1;bool operator<(const string& s1, const string& s2){size_t begin1 = 0, begin2 = 0;while (begin1 < s1.size() && begin2 < s2.size()){if (s1[begin1] > s2[begin2]){return false;}else if (s1[begin1] < s2[begin2]){return true;}else{begin1++;begin2++;}}return begin2 < s2.size() ? true : false;}bool operator==(const string& s1, const string& s2){return strcmp(s1.c_str(), s2.c_str());}bool operator>(const string& s1, const string& s2){return !(s1 < s2 || s1 == s2);}bool operator<=(const string& s1, const string& s2){return !(s1 > s2);}bool operator>=(const string& s1, const string& s2){return !(s1 < s2);}ostream& operator<<(ostream& out, const string& s){///*out << s.c_str();*/不能这么写for (auto e : s){out << e;}return out;}istream& operator>>(istream& in, string& s){s.clear();char ch = in.get();while (ch != '\n'){//s += ch;s += ch;ch = in.get();}return in;}void test_string1(){string s1;string s2("hello world");string s3(s2);s1 = s2;s2 = s2;cout << s1.c_str() << endl;cout << s1.size() << endl;//cout << s1[s1.size() - 1] << endl;cout << s1[s1.size()] << endl;}void test_string2(){string s1;s1.push_back('H');s1.append("ell");s1.append("o world");string::iterator it = s1.begin();while (it != s1.end()){cout << *it << " ";it++;}//s1.reserve(1000);//s1.resize(100);/*s1 += ' ';s1 += "hello mom";*/}void test_string3(){string s1;/*s1.push_back('H');s1.append("ell");s1.append("o world");*/s1.insert('H', s1.size());s1.insert("ell", s1.size());s1.insert("o world", s1.size());string::iterator it = s1.begin();while (it != s1.end()){cout << *it << " ";it++;}cout << endl;cout << s1.find('H') << endl;cout << s1.find("world") << endl;//s1.erase(0);s1.erase(5, 1);//s1.erase(0, 6);it = s1.begin();while (it != s1.end()){cout << *it << " ";it++;}cout << endl;/*string s2(s1);it = s2.begin();while (it != s2.end()){cout << *it << " ";it++;}cout << endl;*/}void test_string4(){string s1("abcd");//string s2("abcd");string s3("abcde");/*cout << (s1 < s2) << endl;cout << (s1 < s3) << endl;*//*cout << (s1 == s3) << endl;cout << (s1 == s2) << endl;*//*s1 += '\0';s1 += "hello";*//*cout << s1 << endl;string s2;cin >> s2;cout << s2;*///s1.clear();cout << s1;}}

test.cpp

#define _CRT_SECURE_NO_WARNINGS 1
#include
using namespace std;
#include
#include
#include"string.h"
int main()
{lzy::test_string1();//lzy::test_string2();//lzy::test_string3();//lzy::test_string4();return 0;
}

vs编译器下的实现