【C++STL精讲】string的模拟实现
文章目录
- 💐专栏导读
- 💐文章导读
- 🌷定义string类
- 🌷构造函数
- 🌷拷贝构造函数
- 🌷赋值重载
- 🌷析构函数
- 🌷[]操作符重载
- 🌷比较运算符重载
- 🌷c_str、size、capacity
- 🌷resize与reserve
- 🌷添加数据 - push_back、append、+=重载
- 🌷insert
- 🌷erase
- 🌷find
- 🌷swap
- 🌷clean
- 🌷迭代器
- 🌷>> 与 << 重载
- 🌷完整源码
💐专栏导读
🌸作者简介:花想云,在读本科生一枚,致力于 C/C++、Linux 学习。
🌸本文收录于 C++系列,本专栏主要内容为 C++ 初阶、C++ 进阶、STL 详解等,专为大学生打造全套 C++ 学习教程,持续更新!
🌸相关专栏推荐:C语言初阶系列 、C语言进阶系列 、数据结构与算法
💐文章导读
本章我们将参照STL源码
,来模拟实现string
类,但不一定非要与库中完全相同。我们将其中重要的、常用的接口进行模拟实现,旨在加深string
类的学习与记忆。
🌷定义string类
为了区别于标准库
中的string
类,我们使用自己的命名空间
,在自己命名空间中模拟实现string
类。
string
类包含这三个基本成员
:
char* _str
字符数组;size_t _size
大小;size_t _capacity
容量;
此外还需声明一个static
成员npos
,npos
为将来实现的某些成员函数的缺省值
,值位-1
;
namespace hxy
{class string{public://...private:char* _str;size_t _size;size_t _capacity;//类中进行声明static const size_t npos;}//类外定义nposconst size_t string::npos = -1;
}
🌷构造函数
string
类提供两种构造方法:
直接构造
;
string str;
传字符串构造
;
string str("hello world");
- 对于传字符串构造的情况,我们可以实现用
const char* str
来接收它; - 对于直接构造的情况,我们可以用
缺省值
来解决;
//构造函数string(const char* str = "") //使用缺省值:_size(strlen(str)){_capacity = _size == 0 ? 3 : _size; //_capacity初始值不能为0_str = new char[_capacity + 1]; //为'\\0'预留位置strcpy(_str, str);}
注意
_capacity
的值不能初始化为0
,因为扩容时可能出现0*n=0
的情况。
🌷拷贝构造函数
我们还会遇到用string
类对象进行构造的情况:
string s1;string s2(s1);
拷贝构造虽然不写,编译器会自动实现,但是自动实现的拷贝构造为浅拷贝
,对于string
类中,成员变量会申请资源
的情况,浅拷贝是行不通的,所以需要我们自己实现。
//拷贝构造string(const string& s):_size(s._size), _capacity(s._capacity){_str = new char[_capacity + 1];strcpy(_str, s._str);}
🌷赋值重载
string s1;string s2 = s1;
//赋值重载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;}return *this;}
🌷析构函数
//析构函数~string(){delete[] _str;_str = nullptr;_size = _capacity = 0;}
🌷[]操作符重载
注意应对cons
t对象与非const对象
须实现不同的重载函数。
//用于const对象只读const char& operator[](size_t pos) const{assert(pos < _size);return _str[pos];}//用于普通对象可读可写char& operator[](size_t pos){assert(pos < _size);return _str[pos];}
🌷比较运算符重载
//比较运算符重载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);}
🌷c_str、size、capacity
c_str
:返回C风格的字符串。size
:返回_size;capacity
:返回_capacity;
const char* c_str(){return _str;}size_t size() const{return _size;}size_t capacity() const{return _capacity;}
🌷resize与reserve
resize
:扩容并初始化;reserve
:只扩容;
void resize(size_t n, char ch = '\\0'){if (n < _size){_str[n] = '\\0';_size = n;}else if (n > _size){if (n > _capacity){reserve(n);}size_t i = _size;while (i < n){_str[i] = ch;++i;}_size = n;_str[_size] = '\\0';}}void reserve(size_t n){if (n > _capacity){char* tmp = new char[n + 1];strcpy(tmp, _str);delete _str;_str = tmp;_capacity = n;}}
🌷添加数据 - push_back、append、+=重载
push_back
:尾插一个字符;append
:尾插一个字符串;+=
:尾插一个字符或字符串;
void push_back(char ch){//考虑扩容if (_size + 1 > _capacity){reserve(_capacity * 2);}_str[_size] = ch;_size++;_str[_size] = '\\0';}void append(const char* str){size_t len = strlen(str);//考虑扩容if (_size+len > _capacity){reserve(_size + len);}strcpy(_str + _size, str);_size += len;}string& operator+=(char ch){push_back(ch);return *this;}string& operator+=(const char* str){append(str);return *this;}
🌷insert
insert
:在pos
位置插入一个字符或字符串;
string& insert(size_t pos, char ch){assert(pos <= _size);if (_size + 1 > _capacity){reserve(_capacity * 2);}size_t end = _size + 1;while (end > pos){_str[end] = _str[end - 1];end--;}_str[pos] = ch;++_size;return *this;}string& insert(size_t pos, const char* str){assert(pos <= _size);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 - 1){_str[end] = _str[end - len];end--;}strncpy(_str + pos, str, len);_size += len;return *this;}
🌷erase
erase
:删除pos
位置向后的n
个字符;
string& 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;}return *this;}
🌷find
find
:从pos
位置开始向后查找指定字符或字符串,并返回起始位置的下标。
size_t find(char ch, size_t pos = npos){assert(pos < _size);for (size_t i = pos; i < _size; ++i){if (_str[i] == ch){return i;}}return npos;}size_t find(const char* str, size_t pos = npos){assert(pos < _size);char* p = strstr(_str, str);if (p == nullptr){return npos;}else{return p - str;}}
🌷swap
swap
:交换两个对象的内容;
void swap(string& s){std::swap(_str, s._str);std::swap(_size, s._size);std::swap(_capacity, s._capacity);}
🌷clean
clean
:清理数据;
void clean(){_str[0] = '\\0';_size = 0;}
🌷迭代器
有了迭代器
,我们就能对自己实现的类使用范围for
了。
//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;}
🌷>> 与 << 重载
注意这两个函数须定义在类外
。
ostream& operator<<(ostream& out, const string& str){for (auto ch : str){out << ch;}return out;}istream& operator>>(istream& in, string& str){str.clean();char ch = in.get();char buff[128]; //避免因频繁扩容导致效率过低size_t i = 0;while (ch != ' ' && ch != '\\n'){buff[i++] = ch;if (i == 127){buff[127] = '\\0';str += buff;i = 0;}ch = in.get();}if (i != 0){buff[i] = '\\0';str += buff;}return in;}
🌷完整源码
#pragma once
#include<assert.h>
#include<iostream>namespace hxy
{class string{public://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;}//构造函数string(const char* str = "") //使用缺省值:_size(strlen(str)){_capacity = _size == 0 ? 3 : _size; //_capacity初始值不能为0_str = new char[_capacity + 1]; //为'\\0'预留位置strcpy(_str, str);}//拷贝构造string(const string& s):_size(s._size), _capacity(s._capacity){_str = new char[_capacity + 1];strcpy(_str, s._str);}//赋值重载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;}return *this;}//析构函数~string(){delete[] _str;_str = nullptr;_size = _capacity = 0;}const char* c_str(){return _str;}//用于const对象只读const char& operator[](size_t pos) const{assert(pos < _size);return _str[pos];}//用于普通对象可读可写char& operator[](size_t pos){assert(pos < _size);return _str[pos];}size_t size() const{return _size;}size_t capacity() const{return _capacity;}//比较运算符重载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);}void resize(size_t n, char ch = '\\0'){if (n < _size){_str[n] = '\\0';_size = n;}else if (n > _size){if (n > _capacity){reserve(n);}size_t i = _size;while (i < n){_str[i] = ch;++i;}_size = n;_str[_size] = '\\0';}}void reserve(size_t n){if (n > _capacity){char* tmp = new char[n + 1];strcpy(tmp, _str);delete _str;_str = tmp;_capacity = n;}}void push_back(char ch){//考虑扩容if (_size + 1 > _capacity){reserve(_capacity * 2);}_str[_size] = ch;_size++;_str[_size] = '\\0';}void append(const char* str){size_t len = strlen(str);//考虑扩容if (_size+len > _capacity){reserve(_size + len);}strcpy(_str + _size, str);_size += len;}string& operator+=(char ch){push_back(ch);return *this;}string& operator+=(const char* str){append(str);return *this;}string& insert(size_t pos, char ch){assert(pos <= _size);if (_size + 1 > _capacity){reserve(_capacity * 2);}size_t end = _size + 1;while (end > pos){_str[end] = _str[end - 1];end--;}_str[pos] = ch;++_size;return *this;}string& insert(size_t pos, const char* str){assert(pos <= _size);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 - 1){_str[end] = _str[end - len];end--;}strncpy(_str + pos, str, len);_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{strcpy(_str + pos, _str + pos + len);_size -= len;}return *this;}void swap(string& s){std::swap(_str, s._str);std::swap(_size, s._size);std::swap(_capacity, s._capacity);}size_t find(char ch, size_t pos = npos){assert(pos < _size);for (size_t i = pos; i < _size; ++i){if (_str[i] == ch){return i;}}return npos;}size_t find(const char* str, size_t pos = npos){assert(pos < _size);char* p = strstr(_str, str);if (p == nullptr){return npos;}else{return p - str;}}void clean(){_str[0] = '\\0';_size = 0;}private:char* _str;size_t _size;size_t _capacity;static const size_t npos;};//定义nposconst size_t string::npos = -1;ostream& operator<<(ostream& out, const string& str){for (auto ch : str){out << ch;}return out;}istream& operator>>(istream& in, string& str){str.clean();char ch = in.get();char buff[128];size_t i = 0;while (ch != ' ' && ch != '\\n'){buff[i++] = ch;if (i == 127){buff[127] = '\\0';str += buff;i = 0;}ch = in.get();}if (i != 0){buff[i] = '\\0';str += buff;}return in;}
}