【CPP】STL容器模拟实现篇之string

全版本string

#pragma once
#include <iostream>
#include <cstring>
#include <assert.h>
#include <list>
using namespace std;
namespace king
{class string{public:const static size_t npos = -1; // const static 可在类内声明同时初始化private:char *_str;size_t _size;size_t _capacity;public:// 无参构造// string()//     : _str(new char[1]), _size(0), _capacity(0)// {//     _str[0] = '\0';// }// 有参不缺省构造// string(const char *str)// {//     // 处理空指针//     if (str == nullptr)//     {//         _size = 0;//         _capacity = 0;//         _str = new char[1];//     }//     // 处理非法结尾//     size_t max_len = 1024 * 1024;//     size_t len = strnlen(str, max_len);//     if (len == max_len)//     {//         _size = len;//         _capacity = len;//         _str = new char[len + 1];//         memcpy(_str, str, len);//         _str[len] = '\0';//     }//     // 正常//     _size = strlen(str);//     _capacity = _size;//     _str = new char[_capacity + 1];//     strcpy(_str, str);// }// 全缺省构造函数string(const char *str = ""){_size = strlen(str);_capacity = _size;_str = new char[_capacity + 1];strcpy(_str, str);/*strncpy_size = strlen(str);_capacity = _size;_str = new char[_capacity + 1];strncpy(_str, str, _size);_str[_size] = '\0';*/}// string s1(s);string(const string &s): _str(new char[s._capacity + 1]), _size(s._size), _capacity(s._capacity){strcpy(_str, s._str);}// 拷贝构造void swap(string &t){::swap(_str, t._str);::swap(_size, t._size);::swap(_capacity, t._capacity);}// string s1(s);string(const string &s): _str(nullptr), _size(0), _capacity(0){string t(s._str);swap(t); // this->swap(t);}// 析构函数~string(){delete[] _str;_str = nullptr;_size = _capacity = 0;}// string s1 = s;string &operator=(const string &s){if (this != &s){// 在析构_str之前 先创建一个临时变量执行new语句// 如果此时出错 程序中止 不会执行delete语句char *tmp = new char[s._capacity + 1];delete[] _str;strcpy(tmp, s._str);_str = tmp;_size = s._size;_capacity = s._capacity;}return *this;}string &operator=(const string &s){if (this != &s){string tmp(s);swap(tmp);}return *this;}string &operator=(string s){swap(s);return *this;}// 移动构造函数string(string &&s) noexcept: _str(s._str), _size(s._size), _capacity(s._capacity){s._str = nullptr;}// 移动赋值运算符string &operator=(string &&s) noexcept{delete[] _str;_str = s._str;_size = s._size;_capacity = s._capacity;s._str = nullptr;return *this;}// c_strconst char *c_str() const{return _str;}// size()size_t size() const{return _size;}// capacity()size_t capacity() const{return _capacity;}// 下标访问char &operator[](size_t pos){assert(pos < _size);return _str[pos];}// 下标访问 constconst char &operator[](size_t pos) const{assert(pos < _size);return _str[pos];}// 迭代器typedef char *iterator;typedef const char *const_iterator;// 头iterator begin(){return _str;}// 尾iterator end(){return _str + _size;}// 头 constconst_iterator begin() const{return _str;}// 尾 constconst_iterator end() const{return _str + _size;}// insert插入字符函数string &insert(size_t pos, char ch){assert(pos <= _size);// 满了就扩容if (_size == _capacity){reserve(_capacity == 0 ? 4 : _capacity * 2);}size_t end = _size + 1;while (end > pos){_str[end] = _str[end - 1];--end;}_str[pos] = ch;++_size;return *this;}// insert插入字符串函数string &insert(size_t pos, const char *str){assert(pos <= _size);// 扩容size_t len = strlen(str);if (_size + len > _capacity){reserve(_size + len);}// 挪动数据size_t end = _size + len;while (end >= pos + len){_str[end] = _str[end - len];--end;}// 拷贝内容strncpy(_str + pos, str, len);_size += len;return *this;}// 删除len个字符void erase(size_t pos, size_t len = npos){assert(pos < _size);if (len == npos || pos + len >= _size){_str[pos] = '\0';_size = pos;}else{strcpy(_str + pos, _str + pos + len);_size -= len;}}// 预留空间void reserve(size_t n){if (n > _capacity){char *tmp = new char[n + 1]; // 开新空间strcpy(tmp, _str);           // 拷贝内容delete[] _str;               // 释放原空间_str = tmp;    // 更新指针指向_capacity = n; // 拷贝容量}}// 预留空间 + 初始化void resize(size_t n, char ch = '\0'){if (n > _size){// 插入数据reserve(n);for (size_t i = _size; i < n; ++i){_str[i] = ch;}_str[n] = '\0';_size = n;}else{// 删除数据_str[n] = '\0';_size = n;}}// 插入字符 push_backvoid push_back(char ch){insert(_size, ch);}// 插入字符串 appendvoid append(const char *str){insert(_size, str);}void append(const string &s){append(s._str);}void append(size_t n, char ch){reserve(_size + n);for (size_t i = 0; i < n; ++i){push_back(ch);}}// +=字符string &operator+=(char ch){push_back(ch);return *this;}// +=字符串string &operator+=(const char *str){append(str);return *this;}// 清空字符串void clear(){_str[0] = '\0';_size = 0;}// find函数查找字符size_t find(char ch, size_t pos = 0) const{assert(pos < _size);for (size_t i = pos; i < _size; ++i){if (ch == _str[i]){return i;}}return npos;}// find函数查找字符串size_t find(const char *sub, size_t pos = 0) const{assert(sub);assert(pos < _size);const char *ptr = strstr(_str + pos, sub);if (ptr == nullptr){return npos;}else{return ptr - _str;}}// substr函数 从pos处取len个字符作为子串返回string substr(size_t pos, size_t len = npos) const{assert(pos < _size);size_t realLen = len;if (len == npos || pos + len > _size){realLen = _size - pos;}string sub;for (size_t i = 0; i < realLen; ++i){sub += _str[pos + i];}return sub;}// 比较大小bool operator>(const string &s) const{return strcmp(_str, s._str) > 0;}// 比较相等bool operator==(const string &s) const{return strcmp(_str, s._str) == 0;}// 判断 >=bool operator>=(const string &s) const{return *this > s || *this == s;}// 判断 <=bool operator<=(const string &s) const{return !(*this > s);}// 判断 <bool operator<(const string &s) const{return !(*this >= s);}// 判断 !=bool operator!=(const string &s) const{return !(*this == s);}};// size_t string::npos = -1;// 流插入// ostream &operator<<(ostream &out, string &s)// {//     out << s._ptr; // 需要声明为友元函数//     return out;// }ostream &operator<<(ostream &out, const string &s){for (size_t i = 0; i < s.size(); ++i)out << s[i];return out;}// 流提取--类比缓冲区 优化代码istream &operator>>(istream &in, string &s){s.clear();char ch;ch = in.get();const size_t N = 32;char buff[N];size_t i = 0;while (ch != ' ' && ch != '\n'){buff[i++] = ch;if (i == N - 1){buff[i] = '\0';s += buff;i = 0;}ch = in.get();}buff[i] = '\0';s += buff;return in;}
}

精简版string

#pragma once
#include <iostream>
#include <cstring>
#include <assert.h>
#include <list>
using namespace std;
namespace king
{class string{public:const static size_t npos = -1; // const static 可在类内声明同时初始化void swap(string &t){::swap(_str, t._str);::swap(_size, t._size);::swap(_capacity, t._capacity);}private:char *_str;size_t _size;size_t _capacity;public:// 全缺省构造函数string(const char *str = ""){_size = strlen(str);_capacity = _size;_str = new char[_capacity + 1];strcpy(_str, str);}// 析构函数~string(){delete[] _str;_str = nullptr;_size = _capacity = 0;}// string s1(s);string(const string &s): _str(nullptr), _size(0), _capacity(0){string t(s._str);swap(t); // this->swap(t);}// 移动构造函数string(string &&s) noexcept: _str(s._str), _size(s._size), _capacity(s._capacity){s._str = nullptr;}string &operator=(string s){swap(s);return *this;}// 移动赋值运算符string &operator=(string &&s) noexcept{delete[] _str;_str = s._str;_size = s._size;_capacity = s._capacity;s._str = nullptr;return *this;}// c_strconst char *c_str() const{return _str;}// size()size_t size() const{return _size;}// capacity()size_t capacity() const{return _capacity;}// 下标访问char &operator[](size_t pos){assert(pos < _size);return _str[pos];}// 下标访问 constconst char &operator[](size_t pos) const{assert(pos < _size);return _str[pos];}// 迭代器typedef char *iterator;typedef const char *const_iterator;// 头iterator begin(){return _str;}// 尾iterator end(){return _str + _size;}// 头 constconst_iterator begin() const{return _str;}// 尾 constconst_iterator end() const{return _str + _size;}// insert插入字符函数string &insert(size_t pos, char ch){assert(pos <= _size);// 满了就扩容if (_size == _capacity)reserve(_capacity == 0 ? 4 : _capacity * 2);size_t end = _size + 1;while (end > pos){_str[end] = _str[end - 1];--end;}_str[pos] = ch;++_size;return *this;}// insert插入字符串函数string &insert(size_t pos, const char *str){assert(pos <= _size);// 扩容size_t len = strlen(str);if (_size + len > _capacity){reserve(_size + len);}// 挪动数据size_t end = _size + len;while (end >= pos + len){_str[end] = _str[end - len];--end;}// 拷贝内容strncpy(_str + pos, str, len);_size += len;return *this;}// 删除len个字符void erase(size_t pos, size_t len = npos){assert(pos < _size);if (len == npos || pos + len >= _size){_str[pos] = '\0';_size = pos;}else{strcpy(_str + pos, _str + pos + len);_size -= len;}}// 预留空间void reserve(size_t n){if (n > _capacity){char *tmp = new char[n + 1]; // 开新空间strcpy(tmp, _str);           // 拷贝内容delete[] _str;               // 释放原空间_str = tmp;    // 更新指针指向_capacity = n; // 拷贝容量}}// 预留空间 + 初始化void resize(size_t n, char ch = '\0'){if (n > _size){// 插入数据reserve(n);for (size_t i = _size; i < n; ++i){_str[i] = ch;}_str[n] = '\0';_size = n;}else{// 删除数据_str[n] = '\0';_size = n;}}// 插入字符 push_backvoid push_back(char ch){insert(_size, ch);}// 插入字符串 appendvoid append(const char *str){insert(_size, str);}void append(const string &s){append(s._str);}void append(size_t n, char ch){reserve(_size + n);for (size_t i = 0; i < n; ++i){push_back(ch);}}// +=字符string &operator+=(char ch){push_back(ch);return *this;}// +=字符串string &operator+=(const char *str){append(str);return *this;}// 清空字符串void clear(){_str[0] = '\0';_size = 0;}// find函数查找字符size_t find(char ch, size_t pos = 0) const{assert(pos < _size);for (size_t i = pos; i < _size; ++i){if (ch == _str[i]){return i;}}return npos;}// find函数查找字符串size_t find(const char *sub, size_t pos = 0) const{assert(sub);assert(pos < _size);const char *ptr = strstr(_str + pos, sub);if (ptr == nullptr){return npos;}else{return ptr - _str;}}// substr函数 从pos处取len个字符作为子串返回string substr(size_t pos, size_t len = npos) const{assert(pos < _size);size_t realLen = len;if (len == npos || pos + len > _size){realLen = _size - pos;}string sub;for (size_t i = 0; i < realLen; ++i){sub += _str[pos + i];}return sub;}// 比较大小bool operator>(const string &s) const{return strcmp(_str, s._str) > 0;}// 比较相等bool operator==(const string &s) const{return strcmp(_str, s._str) == 0;}// 判断 >=bool operator>=(const string &s) const{return *this > s || *this == s;}// 判断 <=bool operator<=(const string &s) const{return !(*this > s);}// 判断 <bool operator<(const string &s) const{return !(*this >= s);}// 判断 !=bool operator!=(const string &s) const{return !(*this == s);}};ostream &operator<<(ostream &out, const string &s){for (size_t i = 0; i < s.size(); ++i)out << s[i];return out;}// 流提取--类比缓冲区 优化代码istream &operator>>(istream &in, string &s){s.clear();char ch;ch = in.get();const size_t N = 32;char buff[N];size_t i = 0;while (ch != ' ' && ch != '\n'){buff[i++] = ch;if (i == N - 1){buff[i] = '\0';s += buff;i = 0;}ch = in.get();}buff[i] = '\0';s += buff;return in;}
}

测试函数

#include "mini_string.hpp"
namespace king
{// 构造、下标访问void test_string1(){// 构造string s1("hello world");string s2; // 若使用无参构造1.0无法输出// c_strcout << s1.c_str() << endl;cout << s2.c_str() << endl;// 下标访问for (size_t i = 0; i < s1.size(); ++i){cout << s1[i] << " ";}cout << endl;// 下标访问constfor (size_t i = 0; i < s1.size(); ++i){s1[i]++;cout << s1[i] << " ";}}// 迭代器void test_string2(){// 迭代器访问string s1("hello world");string::iterator it = s1.begin();while (it != s1.end()){*it += 1;cout << *it << " ";++it;}cout << endl;// 迭代器--范围forfor (auto ch : s1){cout << ch << " ";}cout << endl;}// 拷贝构造void test_string3(){string s1("hello world");string s2(s1);cout << s1.c_str() << endl;cout << s2.c_str() << endl;s2[0] = 'x';cout << s1.c_str() << endl;cout << s2.c_str() << endl;string s3("111111111111111111111111111111");s1 = s3;// 默认的赋值存在的问题：// 1.s1._str指向空间的地址丢失// 2.对同一块空间析构两次cout << s1.c_str() << endl;cout << s3.c_str() << endl;s1 = s1;cout << s1.c_str() << endl;cout << s3.c_str() << endl;}// 两个swap函数// 增加字符void test_string5(){string s1("hello");cout << s1.c_str() << endl;s1.push_back('x');cout << s1.c_str() << endl;cout << s1.capacity() << endl;s1 += 'y';s1 += 'z';s1 += 'z';s1 += 'z';s1 += 'z';s1 += 'z';s1 += 'z';cout << s1.c_str() << endl;cout << s1.capacity() << endl;}// 增加字符串void test_string6(){string s1("hello");cout << s1.c_str() << endl;s1 += ' ';s1.append("world");s1 += "bit hello";cout << s1.c_str() << endl;}// 插入字符、字符串void test_string7(){string s1("hello");cout << s1.c_str() << endl;s1.insert(5, '#');cout << s1.c_str() << endl;s1.insert(0, '#');cout << s1.c_str() << endl;s1.insert(2, "world");cout << s1.c_str() << endl;s1.insert(0, "world ");cout << s1.c_str() << endl;}// 删除字符、字符串void test_string8(){string s1("hello");s1.erase(1, 10);cout << s1.c_str() << endl;string s2("hello");s2.erase(1);cout << s2.c_str() << endl;string s3("hello");s3.erase(1, 2);cout << s3.c_str() << endl;}// 流插入、流提取void test_string9(){string s1("hello");cout << s1 << endl;cout << s1.c_str() << endl;s1 += '\0';s1 += "world";cout << s1 << endl;cout << s1.c_str() << endl;string s3, s4;cin >> s3 >> s4;cout << s3 << s4 << endl;}// find、substrvoid DealUrl(const string &url){size_t pos1 = url.find("://");if (pos1 == string::npos){cout << "非法url" << endl;return;}string protocol = url.substr(0, pos1);// 从网址首部取pos1个字符作为子串cout << protocol << endl;size_t pos2 = url.find('/', pos1 + 3);if (pos2 == string::npos){cout << "非法url" << endl;return;}string domain = url.substr(pos1 + 3, pos2 - pos1 - 3);cout << domain << endl;string uri = url.substr(pos2 + 1);cout << uri << endl<< endl;}void test_string10(){string url1 = "https://cplusplus.com/reference/string/string/";string url2 = "ftp://ftp.cs.umd.edu/pub/skipLists/skiplists.pdf";DealUrl(url1);DealUrl(url2);}// resize函数：开空间 + 初始化void test_string11(){string s1;s1.resize(20);string s2("hello");s2.resize(20, 'x');s2.resize(10);}// vs对于string类的优化void test_string12(){std::string s0;std::string s1("111111");std::string s2("11111111111111111111111111111111111111111");cout << sizeof(s0) << endl; // 40cout << sizeof(s1) << endl; // 40cout << sizeof(s2) << endl; // 40// 理论上：sizeof(s) == 12// 实  际：string还有第4个成员变量// 不同vs版本不同 此VS2022下：char _buff[28]//_size <  28 :字符串存放在_buff数组中//_size >= 28 :            _str指向的堆空间上}
}void test_string4()
{string s1("hello world");string s2("xxxxxxx");// s1.swap(s2);// 模拟实现string类的成员函数：void swap(string& t)//==>   原string类的成员函数：void std::string::swap(string & str);// 作用：交换类的成员变量（_str交换地址）s1.swap(s2);// 全局域的swap函数：/*template <class T>void std::swap(T & a, T & b);{T c(a);a = b;b = a;}*/// 作用：经历了拷贝构造+赋值运算 a b 的_str指向空间的地址均被更新std::swap(s1, s2);::swap(s1, s2);
}int main()
{king::test_string1();return 0;
}