C++ ─── string的完整模拟实现

本博客实现了string的常见接口实现

下面是用到的一些函数，供大家回顾复习

string.h

cpp 复制代码

#define _CRT_SECURE_NO_WARNINGS 1
#pragma once
#include<iostream>
#include<assert.h>
using namespace std;

namespace bit
{
	class string
	{
	public:
		typedef char* iterator;
		typedef const char* const_iterator;

		iterator begin();
		iterator end();

		const_iterator begin() const;
		const_iterator end() const;

		//string();
		string(const char* str = "");
		string(const string& s);
		string& operator=(const string& s);
		~string();

		const char* c_str() const;

		size_t size() const;
		size_t capacity() const;
		char& operator[](size_t pos);
		const char& operator[](size_t pos) const;

		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);//在pos前面插入
		void insert(size_t pos, const char* str);
		void erase(size_t pos = 0, size_t len = npos);//从pos开始删除

		size_t find(char ch, size_t pos = 0);
		size_t find(const char* str, size_t pos = 0);

		void swap(string& s);
		string substr(size_t pos = 0, size_t len = npos);

		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;
		void clear();
	private:
		//char _buff[16];
		char* _str;

		size_t _size;
		size_t _capacity;

		//	  
		//	const static size_t npos = -1;

		//	 ֧
		//	const static double N = 2.2;

		const static size_t npos;
	};

		istream& operator>> (istream& is, string& str);
		ostream& operator<< (ostream& os, const string& str);
}

string.cpp

cpp 复制代码

#define _CRT_SECURE_NO_WARNINGS 1
#include"string.h"

namespace bit
{
	const size_t string::npos = -1;//重要
	string::iterator string::begin()
	{
		return _str;
	}
	string::iterator string::end()
	{
		return _str + _size;
	}

	string::const_iterator string::begin() const
	{
		return _str;
	}
	string::const_iterator string::end() const
	{
		return _str + _size;
	}

	//string();
	string::string(const char* str)
		:_size(strlen(str))
	{
		_str = new char[_size + 1];//为'\0'也开位置
		strcpy(_str, str);
		_capacity = _size;
	}
	//s1(s2)
	string::string(const string& s)
	{
		_str = new char[s._capacity+1];
		strcpy(_str, s._str);
		_size = s._size;
		_capacity = s._capacity;
	}
	//s3=s1;
	//s1=s1;
	string& 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;
	}
	string::~string()
	{
		delete[] _str;
		_str = nullptr;
		_size = _capacity = 0;
	}
	const char* string::c_str() const
	{
		return _str;
	}
	size_t string::size() const
	{
		return _size;
	}
	size_t string::capacity() const
	{
		return _capacity;
	}
	char& string::operator[](size_t pos)
	{
		assert(pos < _size);
		return _str[pos];
	}
	const char& string::operator[](size_t pos) const
	{
		assert(pos < _size);
		return _str[pos];
	}
	void string::reserve(size_t n)
	{
		if (n > _capacity)
		{
			char* tmp = new char[n + 1];
			strcpy(tmp, _str);//复制字符串最后是'\0'
			delete[] _str;
			_str = tmp;
			_capacity = n;
		}
	}

	void string::push_back(char ch)//等价与+=(char ch)
	{
		if (_size == _capacity)
		{
			size_t newcapacity = _capacity == 0 ? 4 : _capacity * 2;
			reserve(newcapacity);
		}
		_str[_size++] = ch;
		_str[_size] = '\0';

	}
	void string::append(const char* str)//等价与+=(const char* ch)
	{
		size_t len = strlen(str);
		if (_size == _capacity)
		{
			size_t newcapacity = _capacity + len;
			reserve(newcapacity);
		}
		//直接从str末尾加入字符串
		strcpy(_str + _size, str);
		_size += len;

	}
	string& string::operator+=(char ch)
	{
		push_back(ch);
		return (*this);
	}
	string& string::operator+=(const char* str)
	{
		append(str);
		return (*this);
	}
	void string::insert(size_t pos, char ch)
	{
		assert(pos < _size + 1);
		if (_size == _capacity)
		{
			size_t newcapacity = _capacity == 0 ? 4 : _capacity * 2;
			reserve(newcapacity);
		}
		//此处有坑pos为无符号整形，end为有符号，在比较时有符号会被转成无符号，如果pos==0就会发生问题
		size_t end = _size + 1;//pos==0时,end最后为0,不会为-1（在无符号整形中-1为无穷大）
		while (end > pos)
		{
			_str[end] = _str[end - 1];
			--end;
		}
		_str[end] = ch;
		_size++;
	}
	void string::insert(size_t pos, const char* str)
	{
		size_t len = strlen(str);
		assert(pos < _size + len);
		if (_size == _capacity)
		{
			size_t newcapacity = _capacity + len;
			reserve(newcapacity);
		}
		//此处有坑pos为无符号整形，end为有符号，在比较时有符号会被转成无符号，如果pos==0就会发生问题
		size_t end = _size + len;//pos==0时,end最后为0
		while (end > pos)
		{
			_str[end] = _str[end - len];
			--end;
		}
		_size += len;
		//while (len)
		//{
		//	_str[end + len - 1] = str[len-1];
		//	--len;
		//}
		memcpy(_str + pos, str, len);
	}
	void string::erase(size_t pos, size_t len)
	{
		assert(pos < _size);
		if (len > _size - pos)
		{
			_str[pos] = '\0';
			_size = pos;
		}
		else
		{
			strcpy(_str + pos, _str + pos + len);
			_size -= len;
		}
	}
	size_t string::find(char ch, size_t pos)
	{
		for (size_t i = pos; i < _size; ++i)
		{
			if (_str[i] == ch)
			{
				return i;
			}
		}
		return npos;//找不到返回-1
	}
	size_t string::find(const char* str, size_t pos)
	{
		char* p = strstr(_str + pos, str);
		return  p - _str;
	}
	//s1.swap(s2);
	void string::swap(string& s)//只需要交换s1和s2
	{
		std::swap(_str,s._str);
		std::swap(_size,s._size);
		std::swap(_capacity,s._capacity);
	}
	string string::substr(size_t pos, size_t len)
	{
		// len大于后面剩余字符，有多少取多少
		if (len > _size - pos)
		{
			string sub(_str + pos);
			return sub;
		}
		else
		{
			string sub;
			sub.reserve(len);
			for (size_t i = 0; i < len; i++)
			{
				sub += _str[pos + i];
			}
			return sub;
		}
	}
	bool string::operator<(const string& s) const
	{
		return strcmp(_str, s._str) < 0;
	}
	bool string::operator>(const string& s) const
	{
		return !(*this <= s);
	}
	bool string::operator<=(const string& s) const
	{
		return *this < s || *this == s;
	}
	bool string::operator>=(const string& s) const
	{
		return !(*this < s) ;
	}
	bool string::operator==(const string& s) const
	{
		return strcmp(_str, s._str) == 0;
	}
	bool string::operator!=(const string& s) const
	{
		return !(*this == s);
	}
	void string::clear()
	{
		_str[0] = '\0';
		_size = 0;
	}

	istream& operator>> (istream& is, string& str)
	{
		str.clear();
		char ch = is.get();
		while (ch != ' ' && 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;
	}
}

test.cpp

cpp 复制代码

#define _CRT_SECURE_NO_WARNINGS 1
#include"string.h"

void test_string1()
{
	bit::string s1("hello csdn");
	bit::string s2;
	std::cout << s1.c_str() << std::endl;
}
void test_string2()
{
	bit::string s1("hello csdn");
	s1[0] = 'X';
	std::cout << s1.c_str() << std::endl;
}
void test_string3()
{
	bit::string s1("hello csdn");
	for (size_t i = 0; i < s1.size(); ++i)
	{
		std::cout << s1[i] << " ";
	}
	std::cout << std::endl;

	bit::string::iterator it1 = s1.begin();
	while (it1 != s1.end())
	{
		std::cout << *it1 << " ";
		++it1;
	}
	std::cout << std::endl;

	for (auto& e : s1)
	{
		e++;
		std::cout << e << " ";
	}
	std::cout << std::endl;

	bit::string s2;
	std::cout << s1.c_str() << std::endl;
	std::cout << s2.c_str();

}
void test_string4()
{
	bit::string s1("hello csdn");
	cout << s1.capacity()<<endl;
	s1.reserve(30);
	cout <<s1.c_str()<< s1.capacity() << endl;

	s1.push_back('s');
	cout << s1.c_str() << s1.capacity() << endl;

	const char* str1 = "tr";
	s1.append(str1);
	cout << s1.c_str() << s1.capacity() << endl;

	s1.append(" 666老毕");
	cout << s1.c_str() << s1.capacity() << endl;
}
void test_string5()
{
	bit::string s1("hello csdn");
	cout << s1.c_str() << endl;
	s1.insert(0,'x');
	cout << s1.c_str() << endl;

	s1.insert(0, "666");
	cout << s1.c_str() << endl;

	s1.erase(0,3);
	cout << s1.c_str() << endl;
}
void test_string6()
{
	bit::string s1("hello csdn");
	size_t ret = s1.find('o');
	if (ret != -1)
	{
		cout << ret << endl;
	}
	size_t ret2 = s1.find("cs");
	if (ret2 != -1)
	{
		cout << ret2 << endl;
	}
}
void test_string7()
{
	bit::string s1("hello csdn");
	bit::string s2("hello");
	cout << s1.c_str() << endl;
	cout << s2.c_str() << endl;
	s1.swap(s2);
	cout << s1.c_str() << endl;
	cout << s2.c_str() << endl;
}
void test_string8()
{
	bit::string url("https://gitee.com/ailiangshilove/cpp-class/blob/master/%E8%AF%BE%E4%BB%B6%E4%BB%A3%E7%A0%81/C++%E8%AF%BE%E4%BB%B6V6/string%E7%9A%84%E6%8E%A5%E5%8F%A3%E6%B5%8B%E8%AF%95%E5%8F%8A%E4%BD%BF%E7%94%A8/TestString.cpp");
	size_t pos1 = url.find(':');
	bit::string url1 = url.substr(0, pos1 - 0);
	cout << url1.c_str() << endl;

	size_t pos2 = url.find('/', pos1 + 3);
	bit::string url2 = url.substr(pos1 + 3, pos2 - (pos1 + 3));
	cout << url2.c_str() << endl;

	bit::string url3 = url.substr(pos2 + 1);
	cout << url3.c_str() << endl;
}

void test_string9()
{
	bit::string s1("hello world");
	cout << s1 << endl;

	cin >> s1;
	cout << s1 << endl;
	bit::string s3(s1);
	cout << s3 << endl;
	bit::string s2("hello BiMenghao");
	s3 = s2;
	cout << s3 << endl;
}
int main()
{
	test_string9();
	return 0;
}