【C++】模拟实现string

 

目录

🌞专栏导读

🌛定义string类

 🌛构造函数

🌛拷贝构造函数

🌛赋值函数

🌛析构函数 

🌛[]操作符重载 

🌛c_str、size、capacity函数 

🌛比较运算符重载 

 🌛resize与reserve函数

🌛push_back、append函数 

🌛insert函数 

🌛erase函数

🌛find函数

 🌛swap函数

🌛clean函数

 🌛迭代器

🌛>> 与 << 重载

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🌞专栏导读

🌟作者简介：日出等日落，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，持续更新！

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本章我们将模拟实现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，这里使用自己的命名空间，在自己的命名空间模拟实现string

string类包含这三个基本成员：

• char* _str 字符数组；
• size_t _size 有效字符大小；
• 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 yxb
{class string{public:private:char* _str;size_t _capacity;size_t _size;//类中声明static const size_t npos;};//类外定义const size_t string::npos = -1;
}

 🌛构造函数

//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

拷贝构造虽然编译器会自动实现，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s3(s2)string(const string& s):_size(s._size),_capacity(s._capacity){_str = new char[s._capacity + 1];strcpy(_str, s._str);}

🌛赋值函数

	//s1 = s3   s1 = s1string& 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;_capacity = _size = 0; }

🌛[]操作符重载 

注意应对const对象与非const对象须实现不同的重载函数。

        char& operator[](size_t pos){assert(pos < _size);return _str[pos];}const char& operator[](size_t pos)const{assert(pos < _size);return _str[pos];}

🌛c_str、size、capacity函数 

• 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;}

🌛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);}

 🌛resize与reserve函数

• resize：扩容并初始化；
• reserve：只扩容；

//扩容void reverse(size_t n){if (n > _capacity){char* tmp = new char[n + 1];strcpy(tmp, _str);delete[] _str;_str = tmp;_capacity = n;}}//扩容+初始化void resize(size_t n, char ch = '\0'){if (n <= _size){//删除数据，保留前n个_size = n;_str[_size] = '\0';}else{if (n > _capacity){reverse(n);}size_t i = _size;while (i < n){_str[i++] = ch;}_size = n;_str[_size] = '\0';}}

🌛push_back、append函数 

• 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){if (_size + 1 > _capacity){reverse(_capacity * 2);}_str[_size] = ch;_size++;_str[_size] = '\0';}void append(const char* str){size_t len = strlen(str);if (_size + len > _capacity){reverse(_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函数 

• insert：在pos位置插入一个字符或字符串；

	void insert(size_t pos, char ch){assert(pos <= _size);if (_size + 1 > _capacity){reverse(2 * _capacity);}size_t end = _size + 1;while (pos < end){_str[end] = _str[end - 1];end--;}_str[pos] = ch;_size++;}void insert(size_t pos, const char* str){assert(pos <= _size);size_t len = strlen(str);if (_size + len > _capacity){reverse(_size + len);}//挪动数据size_t end = _size + len;while ( end > pos +len-1 ){_str[end] = _str[end-len];end--;}//拷贝插入 strncpy(_str + pos, str, len);_size += len;}

🌛erase函数

• erase：删除pos位置向后的n个字符；

	void erase(size_t pos, size_t len = npos){if (len == npos || pos + len >= _size){_str[pos] = '\0';_size = pos;}//0123456789else{strcpy(_str + pos, _str + pos + len);_size -= pos;}}

🌛find函数

• 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函数

	void swap(string& s){std::swap(_str, s._str);std::swap(_size, s._size);std::swap(_capacity, s._capacity);}

🌛clean函数

• clean：清理数据；

	void clean(){_str[0] = '\0';_size = 0;}

 🌛迭代器

	//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;}

🌛完整代码

#pragma once
#include<assert.h>namespace yxb
{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]), _size(0),_capacity(0){_str[0] = '\0';}*/string(const char* str = ""):_size(strlen(str)){_capacity = _size == 0 ? 3 : _size;_str = new char[_capacity + 1];strcpy(_str, str);}//拷贝构造s3(s2)string(const string& s):_size(s._size),_capacity(s._capacity){_str = new char[s._capacity + 1];strcpy(_str, s._str);}//s1 = s3   s1 = s1string& 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;}~string(){delete[] _str;_str = nullptr;_capacity = _size = 0; }const char* c_str(){return _str;}char& operator[](size_t pos){assert(pos < _size);return _str[pos];}const char& operator[](size_t pos)const{assert(pos < _size);return _str[pos];}size_t size()const{return _size;}size_t capacity()const{return _capacity;}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);}//扩容void reverse(size_t n){if (n > _capacity){char* tmp = new char[n + 1];strcpy(tmp, _str);delete[] _str;_str = tmp;_capacity = n;}}//扩容+初始化void resize(size_t n, char ch = '\0'){if (n <= _size){//删除数据，保留前n个_size = n;_str[_size] = '\0';}else{if (n > _capacity){reverse(n);}size_t i = _size;while (i < n){_str[i++] = ch;}_size = n;_str[_size] = '\0';}}void push_back(char ch){if (_size + 1 > _capacity){reverse(_capacity * 2);}_str[_size] = ch;_size++;_str[_size] = '\0';}void append(const char* str){size_t len = strlen(str);if (_size + len > _capacity){reverse(_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;}void insert(size_t pos, char ch){assert(pos <= _size);if (_size + 1 > _capacity){reverse(2 * _capacity);}size_t end = _size + 1;while (pos < end){_str[end] = _str[end - 1];end--;}_str[pos] = ch;_size++;}void insert(size_t pos, const char* str){assert(pos <= _size);size_t len = strlen(str);if (_size + len > _capacity){reverse(_size + len);}//挪动数据size_t end = _size + len;while ( end > pos +len-1 ){_str[end] = _str[end-len];end--;}//拷贝插入 strncpy(_str + pos, str, len);_size += len;}void erase(size_t pos, size_t len = npos){if (len == npos || pos + len >= _size){_str[pos] = '\0';_size = pos;}//0123456789else{strcpy(_str + pos, _str + pos + len);_size -= pos;}}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 swap(string& s){std::swap(_str, s._str);std::swap(_size, s._size);std::swap(_capacity, s._capacity);}void clean(){_str[0] = '\0';_size = 0;}private:char* _str;size_t _capacity;size_t _size;static const size_t npos;};const 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]; //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;}void test_string1(){	string s1;string s2("hello world");cout << s1.c_str() << endl;cout << s2.c_str() << endl;s2[0]++;cout << s2.c_str() << endl;}void test_string2(){string s1;string s2("hello world");cout << s1.c_str() << endl;cout << s2.c_str() << endl;s1 = s2;cout << s1.c_str() << endl;cout << s2.c_str() << endl;}void test_string3(){string s1;string s2("hello world");cout << s1.c_str() << endl;cout << s2.c_str() << endl;string::iterator it = s2.begin();while (it != s2.end()){cout << *it << endl;++it;}}void test_string4(){string s1;string s2("hello world");string s3("hello");cout << s1.c_str() << endl;cout << s2.c_str() << endl;cout << (s3 >= s2) << endl;}void test_string5(){string s1;string s2("hello world");s2.append("yyyyyy");cout << s2.c_str() << endl;}void test_string6(){string s1("hhh ");cout << s1.c_str() << endl;s1.resize(10, 'x');cout << s1.c_str() << endl;s1.resize(100, 'y');cout << s1.c_str() << endl;}void test_string7(){string s1("123456789");cout << s1.c_str() << endl;s1.insert(2, "wwww");cout << s1.c_str() << endl;s1.insert(0, "ss");cout << s1.c_str() << endl;}void test_string8(){string s1("123456789");cout << s1.c_str() << endl;s1.erase(4, 2);cout << s1.c_str() << endl;}void test_string9(){string s1;cin >> s1;cout << s1 << endl;}
}