string类的模拟实现的一些改进

上回我们完成了string类的模拟实现，不过之前写的传统写法本篇，我们将要对其进行一些改进，写成参考的是现代写法，这样写可以提高可读性。

上回我们写好的string类

//string.h

#pragma once#define _CRT_SECURE_NO_WARNINGS 1
#pragma once
#include<iostream>
#include<assert.h>
using namespace std;namespace STring
{class string{public:typedef char* iterator;typedef const char* const_iterator;iterator begin();iterator end();const_iterator begin() const;const_iterator end() const;//string();string(const char* str = "");string(const string& s);string& operator=(const string& s);~string();const char* c_str() const;size_t size() const;char& operator[](size_t pos);const char& operator[](size_t pos) const;void reserve(size_t n);void push_back(char ch);void append(const char* str);string& operator+=(char ch);string& operator+=(const char *str);void insert(size_t pos, char ch);void insert(size_t pos, const char* str);void erase(size_t pos = 0, size_t len = npos);size_t find(char ch, size_t pos = 0);size_t find(const char* str, size_t pos = 0);void swap(string& s);string substr(size_t pos = 0, size_t len = npos);bool operator<(const string& s) const;bool operator>(const string& s) const;bool operator<=(const string& s) const;bool operator>=(const string& s) const;bool operator==(const string& s) const;bool operator!=(const string& s) const;void clear();private:// char _buff[16];char* _str;size_t _size;size_t _capacity;//  //const static size_t npos = -1;// ֧//const static double N = 2.2;const static size_t npos;};istream& operator>> (istream& is, string& str);ostream& operator<< (ostream& os, const string& str);
}

//string.cpp

#include"string.h"
namespace STring
{const size_t string::npos = -1;string::iterator string::begin(){return _str;}string::const_iterator string::begin() const{return _str;}string::iterator string::end(){return _str + _size;}string::const_iterator string::end() const{return _str+_size;}string:: string(const char* str):_size(strlen(str)){_str = new char[_size+1];_capacity = _size+1;strcpy(_str, str);}string::string(const string& s){_str = new char[s._capacity];strcpy(_str, s._str);_size = s._size;_capacity = s._capacity;}string::~string(){delete[] _str;_str = nullptr;_size = _capacity = 0;}const char* string::c_str() const{return _str;}size_t string :: size() const{return _size;}void string::reserve(size_t n){if (n > _capacity){char* tmp = new char[n + 1];strcpy(tmp, _str);delete[] _str;_str = tmp;_capacity = n;}}void string::push_back(char ch){if (_size == _capacity){size_t newcapacity = _capacity == 0 ? 4 : _capacity * 2;reserve(newcapacity);}_str[_size] = ch;_str[_size + 1] = '\0';++_size;}void string::append(const char* str){size_t len = strlen(str);if (_size + len > _capacity){reserve(_size + len);}strcpy(_str + _size, _str);_size += len;insert(_size, _str);}void string::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] + 1;--end;}_str[pos] = ch;++_size;}void string::insert(size_t pos, const char* str){assert(pos <= _size);int len = strlen(str);if (_size + len > _capacity){reserve(_capacity+len);}size_t end = _size + len;while (end > pos+len+1){_str[end] = _str[end - len];--end;}memcpy(_str+pos,str,len);_size += len;}void string::erase(size_t pos, size_t len){assert(pos < _size);if (len >= _size - pos){_str[pos] = '\0';_size = len;}else{strcpy(_str + pos, _str + pos + len);_size = len;}}size_t string::find(char ch, size_t pos){for (size_t i = pos; i < _size; i++){if (_str[i] == ch){return i;}}return npos;}size_t string::find(const char* str, size_t pos){char* p = strstr(_str + pos, str);return p - _str;}void string::swap(string& s){std::swap(_str, s._str);std::swap(_size, s._size);std::swap(_capacity, s._capacity);}string string::substr(size_t pos, size_t len){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[i + pos];}return sub;}}string& string:: operator=(const string& s){if (this != &s){char* tmp = new char[s._capacity];strcpy(tmp, s._str);delete[] _str;_str = tmp;_size = s._size;_capacity = s._capacity;}return *this;}char& string::operator[](size_t pos){if (pos < _size)return _str[pos];}const char& string::operator[](size_t pos) const{if (pos < _size)return _str[pos];}string& string::operator+=(char ch){push_back(ch);return *this;}string& string::operator+=(const char* str){append(str);return *this;}bool string::operator<(const string& s) const{return strcmp(_str, s._str) < 0;}bool string::operator>(const string& s) const{return !(*this <= s);}bool string::operator<=(const string& s) const{return *this < s || *this == s;}bool string::operator>=(const string& s) const{return !(*this < s);}bool string::operator==(const string& s) const{return strcmp(_str, s._str) == 0;}bool string::operator!=(const string& s) const{return !(*this == s);}void string::clear(){_str[0] = '\0';_size = 0;}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;}
}

以下是现代写法对于 传统写法的改进

一、push_back

传统写法：

void string::push_back(char ch)
{if (_size == _capacity){size_t newcapacity = _capacity == 0 ? 4 : _capacity * 2;reserve(newcapacity);}_str[_size] = ch;_str[_size + 1] = '\0';++_size;
}

现代写法：

	void string::push_back(char ch){insert(_size, ch);}

二、append

传统写法：

	void string::append(const char* str){size_t len = strlen(str);if (_size + len > _capacity){reserve(_size + len);}strcpy(_str + _size, _str);_size += len;insert(_size, _str);}

现代写法：

	void string::append(const char* str){insert(_size, str);}