string的模擬實現

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一、淺拷貝和深拷貝

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1.淺拷貝

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2.深拷貝

如果一個類中涉及到資源的管理，其拷貝構造函數、賦值運算符重載以及析構函數必須要顯式給出
一般情況都是按照 深拷貝 提供

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3.寫時拷貝

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二、定義string的成員變量

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三、string的接口實現

1.string的默認成員函數

（1）構造函數實現

這種短小頻繁調用的函數，可以直接定義到類里面，默認是 inline

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（2）析構函數實現

這里要注意一下判斷 str是否為空

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（3）拷貝構造函數

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（4）賦值運算符重載

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2.string的迭代器實現

string中迭代器iterator就是一個指針。所以我們直接使用typedef實現
begin（）和end（） 本質上都是 指針

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3.string的容量操作函數

size（）、capacity（）、clear（）、empty（）都很簡單！一看就懂！

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接下來是reserve()，只要新容量大于舊容量就發生擴容。

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4.string的訪問操作函數

這部分較為簡單，其實就是 數組的下表訪問[ ] 和 front()與back()

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5.string的修改操作函數

兩個常用的修改函數： push_back()與append()

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+=就是在push_back和append的應用！

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insert有兩種類型，第一種類似于頭插，第二種類似于任意位置插入
二者都需要挪動數據和檢驗數組的擴容問題

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pop_back函數較為簡單！
字符串的刪除函數erase函數類似于尾刪，也可以任意位置刪除
將pos位置后所有字符往前移動len個單位，如果為字符len=1，否則len=字符串長度

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6.string的查找函數

find函數既可以查找字符，也可以查找字符串（用strstr函數）

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7.string的c_str和substr

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8.string的< <= > >= == !=

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9.string的operator>>

注意普通istream對象無法提前空格與\n。這是我們就需要一個函數get()來提取

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四、源代碼總結

1.String.h

代碼如下（示例）：

#define _CRT_SECURE_NO_WARNINGS 1
#pragma once
#include<iostream>
#include<string>
#include<assert.h>
using namespace std;
namespace bit
{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():_str(new char[1]{'\0'}),_size(0),_capacity(0){}*/// 短小頻繁調用的函數，可以直接定義到類里面，默認是inlinestring(const char* str = ""){_size = strlen(str);// _capacity不包含\0_capacity = _size;_str = new char[_capacity + 1];strcpy(_str, str);}// 深拷貝問題// s2(s1)/*string(const string& s){_str = new char[s._capacity + 1];strcpy(_str, s._str);_size = s._size;_capacity = s._capacity;}*/void swap(string& s){std::swap(_str, s._str);std::swap(_size, s._size);std::swap(_capacity, s._capacity);}// s2(s1)// 現代寫法string(const string& s){string tmp(s._str);swap(tmp);}// s2 = s1// s1 = s1/*string& operator=(const string& s){if (this != &s){delete[] _str;_str = new char[s._capacity + 1];strcpy(_str, s._str);_size = s._size;_capacity = s._capacity;}return *this;}*/// s1 = s3;//string& operator=(const string& s)//{//	if (this != &s)//	{//		//string tmp(s._str);//		string tmp(s);//		swap(tmp);//	}//	return *this;//}// s1 = s3;string& operator=(string tmp){swap(tmp);return *this;}~string(){if (_str){delete[] _str;_str = nullptr;_size = _capacity = 0;}}const char* c_str() const{return _str;}void clear(){_str[0] = '\0';_size = 0;}bool empty() const{return _size == 0;}size_t size() const{return _size;}size_t capacity() const{return _capacity;}// 可讀可寫char& front(){return _str[0];}char& back(){return _str[_size - 1];}// 可讀不可寫const char& front()const{return _str[0];}const char& back()const{return _str[_size - 1];}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 copy_on_write(){if (count > 1){深拷貝}}*/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, size_t len = npos);size_t find(char ch, size_t pos = 0);size_t find(const char* str, size_t pos = 0);string substr(size_t pos = 0, size_t len = npos);private://char _buff[16];char* _str = nullptr;size_t _size = 0;size_t _capacity = 0;//static const size_t npos = -1;static const size_t npos;/*static const int N = 10;int buff[N];*/};bool operator<(const string& s1, const string& s2);bool operator<=(const string& s1, const string& s2);bool operator>(const string& s1, const string& s2);bool operator>=(const string& s1, const string& s2);bool operator==(const string& s1, const string& s2);bool operator!=(const string& s1, const string& s2);ostream& operator<<(ostream& out, const string& s);istream& operator>>(istream& in, string& s);
}

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2.String.cpp

代碼如下（示例）：

#include"string.h"namespace bit
{const size_t string::npos = -1;void string::reserve(size_t n){if (n > _capacity){//cout << "reserve:" << n << endl;char* tmp = new char[n + 1];strcpy(tmp, _str);delete[] _str;_str = tmp;_capacity = n;}}void string::push_back(char ch){if (_size == _capacity){reserve(_capacity == 0 ? 4 : _capacity * 2);}_str[_size] = ch;++_size;_str[_size] = '\0';}string& string::operator+=(char ch){push_back(ch);return *this;}void string::append(const char* str){size_t len = strlen(str);if (_size + len > _capacity){// 大于2倍，需要多少開多少，小于2倍按2倍擴reserve(_size + len > 2 * _capacity ? _size + len : 2 * _capacity);}strcpy(_str + _size, str);_size += len;}string& string::operator+=(const char* str){append(str);return *this;}void string::insert(size_t pos, char ch){assert(pos <= _size);if (_size == _capacity){reserve(_capacity == 0 ? 4 : _capacity * 2);}// 挪動數據size_t end = _size + 1;while (end > pos){_str[end] = _str[end - 1];--end;}_str[pos] = ch;++_size;}void string::insert(size_t pos, const char* s){assert(pos <= _size);size_t len = strlen(s);if (_size + len > _capacity){// 大于2倍，需要多少開多少，小于2倍按2倍擴reserve(_size + len > 2 * _capacity ? _size + len : 2 * _capacity);}size_t end = _size + len;while (end > pos + len - 1){_str[end] = _str[end - len];--end;}for (size_t i = 0; i < len; i++){_str[pos + i] = s[i];}_size += len;}void string::erase(size_t pos, size_t len){assert(pos < _size);if (len >= _size - pos){_str[pos] = '\0';_size = pos;}else{for (size_t i = pos + len; i <= _size; i++){_str[i - len] = _str[i];}_size -= len;}}size_t string::find(char ch, size_t pos){assert(pos < _size);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){assert(pos < _size);const char* ptr = strstr(_str + pos, str);if (ptr == nullptr){return npos;}else{return ptr - _str;}}string string::substr(size_t pos, size_t len){assert(pos < _size);// len大于剩余字符長度，更新一下lenif (len > _size - pos){len = _size - pos;}string sub;sub.reserve(len);for (size_t i = 0; i < len; i++){sub += _str[pos + i];}return sub;}bool operator<(const string& s1, const string& s2){return strcmp(s1.c_str(), s2.c_str()) < 0;}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);}bool operator==(const string& s1, const string& s2){return strcmp(s1.c_str(), s2.c_str()) == 0;}bool operator!=(const string& s1, const string& s2){return !(s1 == s2);}ostream& operator<<(ostream& out, const string& s){for (auto ch : s){out << ch;}return out;}// 17：16繼續istream& operator>>(istream& in, string& s){s.clear();const int N = 256;char buff[N];int i = 0;char ch;//in >> ch;ch = in.get();while (ch != ' ' && ch != '\n'){buff[i++] = ch;if (i == N - 1){buff[i] = '\0';s += buff;i = 0;}//in >> ch;ch = in.get();}if (i > 0){buff[i] = '\0';s += buff;}return in;}
}

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