文章目录
- 🚀1.构造与析构函数
- 🚀2.迭代器
- 🚀3.获取
- 🚀 4.内存修改
- 🚀5. 插入
- 🚀6. 删除
- 🚀7. 查找
- 🚀8. 交换swap
- 🚀9. 截取substr
- 🚀10. 比较符号重载
- 🚀11. 清除
- 🚀12.流插入与流提取
大家好!本文会模拟一个基本的string类,帮助我们更好的理解string的内置函数的实现与规则。
先在.h文件声明每个需要实现的函数,需要实现的成员:
namespace bit
{class string{public://1. 构造函数string(const char* tmp= "");string(const string& tmp);string&operator=(const string& s);~string();//2. 迭代器typedef char* iterator;typedef const char* const_iterator;iterator begin();iterator end();const_iterator begin() const;const_iterator end() const;//3. 获取size_t size() const;char& operator[](size_t pos);const char& operator[](size_t pos) const;//4. 内存修改void reserve(size_t n);//5. 插入string& operator+=(char ch);string& operator+=(const char* str);void push_back(char c);void append(const char* tmp);void insert(int pos, char c);void insert(int pos, const char* tmp);//6. 删除void erase(size_t pos = 0, size_t len = npos);//7. 查找size_t find(char ch, size_t pos = 0);size_t find(const char* str, size_t pos = 0);//8. 交换swapvoid swap(string& s);//9. 截取substrstring substr(size_t pos = 0, size_t len = npos);//10. 比较符号重载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;//11. 清除void clear();private:char* _ptr;size_t _capacity;size_t _size;const static size_t npos = -1;};//12.流插入与流提取istream& operator>> (istream& is, string& str);ostream& operator<< (ostream& os, const string& str);
}
备注(重要):npos是 const static修饰的变量,它实际上不在类中,其在.h声明后,必须在.cpp的全局域(如果有命名空间限定则在命名空间中)定义赋值。这里在.h给予一个缺省值也能到达定义的效果,但是仅限整形!!,double类型或者其他的任何类型都不能在声明时给缺省值
接下来在另一个.cpp后缀的文件中一步一步的剖析实现。
注意
:
- 在.h声明的函数的形参如果有缺省值,.cpp去实现的函数的形参是不带缺省值的
- 我这边模拟的string是放在命名bit里面的,在.cpp去实现时,也要放在bit内实现(就是把实现的函数全部用命名空间bit包起来)
🚀1.构造与析构函数
//1. 构造函数string(const char* tmp= "");string(const string& tmp);string&operator=(const string& s);~string();
- string::string(const char* tmp):
string::string(const char* tmp) :_size(strlen(tmp))
{_ptr = new char[_size + 1];_capacity = _size;strcpy(_ptr,tmp);
}
备注:其中运用到初始化列表的知识,可以到C++入门 类和对象:深入构造函数,static成员,友元函数这个链接了解了解。
2. string(const string& tmp):
string::string(const string& tmp)
{string s(tmp);swap(s);
}
备注:这是一个比较流氓的写法,生成一个临时的 s去拷贝tmp,然后直接用swap函数交换s里面的内容,完成了拷贝tmp里的内容,同时s在到了生命周期也自动的将释放之前在_ptr指针指向的空间 (注:这个swap函数是我们实现的string内置的函数,它的实现在后文,作用就是交换private里面的三个成员参数:_ptr _capacity _size )
- string& operator=(const string& s)
string& string::operator=(const string& s){string s(tmp);swap(s);
}
备注:赋值重载用的方法与拷贝构造(上一个实现的函数)相同。
4. ~string():
string::~string()
{delete[] _ptr;_capacity = _size = 0;
}
备注:释放_ptr指向的空间
🚀2.迭代器
typedef char* iterator;
typedef const char* const_iterator;
iterator string::begin()
{return _ptr;
}
iterator string::end()
{return _ptr+ _size;
}
const_iterator string::begin() const
{return _ptr;
}
const_iterator string::end() const
{return _ptr+ _size;
}
备注: begin()返回首元素的指针,end()返回尾元素下一个位置的指针,当然也要多实现一个const的版本,以适应const string类型。
🚀3.获取
//3. 获取size_t string::size() const{return _size;}size_t string::capacity() const{return _capacity;}char& string::operator[](size_t pos){return _ptr[pos];}const char& string::operator[](size_t pos) const{return _ptr[pos];}
备注:其中运用到运算符重载的知识,可以到这个链接了解了解。C++入门 类和对象:深入构造函数,static成员,友元函数
🚀 4.内存修改
//4. 内存修改
void string::reserve(size_t n)
{if(n > _capacity){iterator tmp = _ptr;_ptr = new char[n+1];_capacity = n;strcpy(ptr, tmp);delete[] _tmp;}
}
备注:用tmp保存原先_ptr指向的空间,_ptr去开新空间,之后拷贝,再释放tmp。这个函数我们不会太经常使用它,但是其他的内部函数经常使用。
🚀5. 插入
//5. 插入void push_back(char c);void append(const char* tmp);void insert(int pos, char c);void insert(int pos, const char* tmp);string& operator+=(char ch);string& operator+=(const char* str);
不同的插入函数代表不同的职能,可以到这个链接去了解C++入门 string类(第一章):string类对象的构造,string类对象的访问即遍历,string类对象的增与删。
push_back:
void string::push_back(char c)
{if(size() == capacity()){int new_capacity = _capacity==0? 4: _capacity*2;reserve(new_capacity);}_ptr[_size] = c;_size++;_ptr[_size] = '\0';
}
备注:先判断是否扩容,再赋值,注意 下标为 _size 位置的是 ‘\0’ ,别忘了在最后补上 ‘\0’
append:
void string::append(const char* tmp)
{int len = strlen(tmp);if(size()+ len >= capacity()){reserve(size()+ len);}strcpy(_ptr+_size,tmp);_size+=len;
}
备注:不用考虑’ \0’的问题,tmp内自带一个’\0’
insert:
void string::insert(int pos, char c)
{if(size() == capacity()){int new_capacity = _capacity==0? 4: _capacity*2;reserve(new_capacity);}int end = size();while(end >= pos){_ptr[end+1] = _ptr[end];}_size++;_ptr[pos] = c;
}
void string::insert(int pos, const char* tmp)
{int len = strlen(tmp);if(size()+ len >= capacity()){reserve(size()+ len);}int end = size() +len;while(end>= pos+len){_prt[end] = _ptr[len-len]}memcpy(_ptr+pos,tmp,len);_size +=len;
}
备注:插入字符串的时,图例:
且不能使用strcpy了,strcpy会同\0一起拷贝,所以这里用memcpy
operator+=:
string& string::operator+=(char ch)
{push_back(ch);
}
string& string::operator+=(const char* str)
{append( str);
}
备注:复用push_back与append
🚀6. 删除
void string::erase(size_t pos , size_t len )
{if(pos+len >= size()){ptr[pos] = '\0';_size = pos+1;}else{strcpy(_ptr+pos,_ptr+pos+len);_size -= len;}
}
备注:从pos开始,删除长度大于size的,直接在pos下标赋值’\0’ ; 除此之外,都将_ptr+pos+len后的字符拷贝到_ptr+pos位置。
🚀7. 查找
//7. 查找size_t find(char ch, size_t pos ){for(int i = 0; i< size();i++){if(ch == _ptr[i])return i;}return npos;}size_t find(const char* str, size_t pos){char* p = strstr(_ptr + pos, str);return p - _ptr;}
备注:查找字符串是直接复用库里的strstr函数。
🚀8. 交换swap
//8. 交换swapvoid swap(string& s){std::swap(s._ptr, _ptr);std::swap(s._size, _size);std::swap(s._capacity, _capacity);}
备注:本质是交换private的三个参数。
🚀9. 截取substr
//9. 截取substrstring substr(size_t pos, size_t len){if(pos+len >= size()){string tmp(_ptr+pos);return tmp;}else{string tmp(_ptr+pos);tmp[len+1] = '\0';tmp._size() = len;return tmp;}}
🚀10. 比较符号重载
//10. 比较符号重载
bool string::operator<(const string& s) const
{return strcmp(this->_ptr, s._ptr)<0 ;
}
bool string::operator>(const string& s) const
{return strcmp(this->_ptr, s._ptr) > 0;
}bool string::operator<=(const string& s) const
{return strcmp(this->_ptr, s._ptr) <= 0;}
bool string::operator>=(const string& s) const
{return strcmp(this->_ptr, s._ptr) >= 0;
}bool string::operator==(const string& s) const
{return !strcmp(this->_ptr, s._ptr);
}
bool string::operator!=(const string& s) const
{return strcmp(this->_ptr, s._ptr);
}
备注:复用的是库里的strcmp函数。一个一个字符比较,不相等就返回结果,字符大小的判断咨询ASCll码
🚀11. 清除
//11. 清除void string::clear(){_size = 0;_ptr[0] = '\0';}
备注:clear同样也可以复用erase去实现
🚀12.流插入与流提取
//12.流插入与流提取istream& operator>> (istream& is, string& str){str.clear();char ch = get();while(ch != '\0'){str+=ch;get();}return is;}ostream& operator<< (ostream& os, const string& str){for (size_t i = 0; i < str.size(); i++){os << str[i];}return os;}
备注:流插入与流提取不是成员函数,实现在类外。 >>重载用到get函数,取得一个输入的字符并尾插到str,当这个字符是换行’\n’时,就不再获取。
全部代码:
//.h
#pragma once
#define _CRT_SECURE_NO_WARNINGS 1
#include <iostream>
#include <cstring>
#include<string>
using namespace std;
namespace bit
{class string{public://构造函数//string();string(const char* tmp= "");string(const string& tmp);string&operator=(const string& s);~string();//迭代器typedef char* iterator;typedef const char* const_iterator;iterator begin();iterator end();const_iterator begin() const;const_iterator end() const;//获取size_t size() const;size_t capacity() const;char& operator[](size_t pos);const char& operator[](size_t pos) const;//内存修改void reserve(size_t n);//插入string& operator+=(char ch);string& operator+=(const char* str);void push_back(char c);void append(const char* tmp);void insert(int pos, char c);void insert(int pos, const char* tmp);//删除void erase(size_t pos = 0, size_t len = npos);//查找size_t find(char ch, size_t pos = 0);size_t find(const char* str, size_t pos = 0);//交换swapvoid swap(string& s);//截取substrstring substr(size_t pos = 0, size_t len = npos);//比较符号重载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;//清除void clear();private:char* _ptr;size_t _capacity;size_t _size;const static size_t npos = -1;};//流插入与流提取istream& operator>> (istream& is, string& str);ostream& operator<< (ostream& os, const string& str);
}//.cpp
#include "string.h"namespace bit
{//构造函数//string();string::string(const char* tmp) :_size(strlen(tmp)){_ptr = new char[_size + 1];_capacity = _size;strcpy(_ptr,tmp);}string::~string(){delete[] _ptr;_capacity = _size = 0;}string& string::operator=(const string& s){//方法1 : 传统方法if (this != &s){char* tmp = new char[s._capacity + 1];strcpy(tmp, s._ptr);delete[] _ptr;_ptr = tmp;_size = s._size;_capacity = s._capacity;}//新派方法,使用swap直接拷贝//string tmp_s(s._ptr);//this->swap(tmp_s);return *this;}string::string(const string& tmp) {//方法1 : 传统方法/*_size = tmp._size ;_capacity = tmp._capacity;_ptr = new char[_capacity + 1];strcpy(_ptr, tmp._ptr);*///方法2 :新派方法,使用swap直接拷贝string tmp_s(tmp._ptr);this->swap(tmp_s);}//迭代器string::iterator string::begin(){return _ptr;}string::iterator string::end(){return _ptr+_size;}string::const_iterator string::begin() const{return _ptr;}string::const_iterator string::end() const{return _ptr + _size;}//获取size_t string::size() const{return _size;}size_t string::capacity() const{return _capacity;}char& string::operator[](size_t pos){return _ptr[pos];}const char& string::operator[](size_t pos) const{return _ptr[pos];}//内存修改void string::reserve(size_t n){if (n > _capacity){iterator tmp = _ptr;_ptr = new char[n + 1];_capacity = n;strcpy(_ptr, tmp);delete[] tmp;}} /*void string::print(){int i = 0;while (i != _size){cout << _ptr[i] ;i++;}}*///插入void string::push_back(char c){if (_size == _capacity){int new_capacity = _capacity == 0 ? 4 : _capacity * 2;reserve(new_capacity);}_ptr[_size] = c;_size++;_ptr[_size] = '\0';}void string::append(const char* tmp){int len = strlen(tmp);if (size() + len >= capacity()){reserve(size() + len);}strcpy(_ptr + _size, tmp);_size += len;}void string::insert(int pos, char c){if (_size == _capacity){int new_capacity = _capacity == 0 ? 4 : _capacity * 2;reserve(new_capacity);}size_t end = _size;while ((int)end >= pos){_ptr[end + 1] = _ptr[end];end--;}_ptr[pos] = c;_size++;}void string::insert(int pos, const char* tmp){int len = strlen(tmp);if (_size + len >= _capacity){reserve(size() + len);}int end = (int)_size + len;while (end >= pos + len){_ptr[end] = _ptr[end - len];end--;}memcpy(_ptr + pos, tmp, len);_size += len;}string& string::operator+=(char ch){this->push_back(ch);return *this;}string& string::operator+=(const char* str){this->append(str);return *this;}//删除void string::erase(size_t pos, size_t len){if (pos + len >= _size){_ptr[pos] = '\0';_size = pos;}else{strcpy(_ptr + pos, _ptr + pos+len);_size -= len;}}//查找size_t string::find(char ch, size_t pos ){for (int i = pos; i < _size; i++){if (ch == _ptr[i]){return i;}}return npos;}size_t string::find(const char* str, size_t pos ){char* p = strstr(_ptr + pos, str);return p - _ptr;}void string::swap(string& s){std::swap(s._ptr, _ptr);std::swap(s._size, _size);std::swap(s._capacity, _capacity);}string string::substr(size_t pos , size_t len){if (pos + len >= _size){string tmp(_ptr + pos);return tmp;}else{string tmp(_ptr + pos);tmp._size = len;tmp._ptr[len] = '\0';return tmp;}}bool string::operator<(const string& s) const{return strcmp(this->_ptr, s._ptr)<0 ;}bool string::operator>(const string& s) const{return strcmp(this->_ptr, s._ptr) > 0;}bool string::operator<=(const string& s) const{return strcmp(this->_ptr, s._ptr) <= 0;}bool string::operator>=(const string& s) const{return strcmp(this->_ptr, s._ptr) >= 0;}bool string::operator==(const string& s) const{return !strcmp(this->_ptr, s._ptr);}bool string::operator!=(const string& s) const{return strcmp(this->_ptr, s._ptr);}void string::clear(){_size = 0;_ptr[0] = '\0';}istream& operator>> (istream& is, string& str){str.clear();char ch = is.get();while ( 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;}}
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