【C++】STL简介 -- string 的使用及其模拟实现

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提取码：yzpq

namespace std {
	template<class T>
	class string {
	public:
		// string 的各种成员函数
		
	private:
		T* _str;
		size_t _size;
		size_t _capacity;
		//string 的其他成员变量，比如npos
	};
}

union _Bxty { 
    // storage for small buffer or pointer to larger one
    value_type _Buf[_BUF_SIZE];
    pointer _Ptr;
    char _Alias[_BUF_SIZE]; // to permit aliasing
} _Bx;

typedef basic_string<char, char_traits, allocator> string

typedef char* iterator;  //简单理解string中的迭代器

#pragma once

#include <iostream>
#include <string.h>
#include <assert.h>
using namespace std;

namespace thj  //将string的实现放在自己的命名空间域里面，防止与std里面的string冲突
{
	class string
	{
	public:
		//---------------------------member functions-------------------------------//
		//构造
		string(const char* str = "")
		{
			int len = strlen(str);
			_size = _capacity = len;  //capacity记录有效字符的个数
			_str = new char[_capacity + 1];  //留一个空间给'\0'
			strcpy(_str, str);
		}

		//析构
		~string()
		{
			delete[] _str;
			_str = nullptr;
			_size = _capacity = 0;
		}

		//拷贝构造--传统写法
		//string(const string& s)
		//{
		//	_size = s._size;
		//	_capacity = s._capacity;
		//	_str = new char[_capacity + 1];
		//	strcpy(_str, s._str);
		//}

		//拷贝构造--现代写法
		string(const string& s)
			:_str(nullptr)
			, _size(0)
			, _capacity(0)
		{
			string tmp(s._str);
			swap(tmp);
		}

		//赋值重载--传统写法
		//string& operator=(const string& s)
		//{
		//	if (this == &s)  //检查自我赋值
		//		return *this;
		//	delete[] _str;
		//	_size = s._size;
		//	_capacity = s._capacity;
		//	_str = new char[_capacity + 1];
		//	strcpy(_str, s._str);
		//	return *this;
		//}

		//赋值重载--现代写法1
		//string& operator=(const string& s)
		//{
		//	if (this == &s)  //检查自我赋值
		//		return *this;
		//	string tmp(s);
		//	swap(tmp);
		//	return *this;
		//}

		//赋值重载--现代写法2
		string& operator=(string s)
		{
			swap(s);
			return *this;
		}

		//--------------------------------------Tterators------------------------------------//
		typedef char* iterator;  //迭代器
		typedef const char* const_iterator;  //const 迭代器

		iterator begin()
		{
			return _str;
		}

		const_iterator begin() const
		{
			return _str;
		}

		iterator end()
		{
			return _str + _size;
		}

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

		//---------------------------------------Capacity--------------------------------------//
		size_t size() const
		{
			return _size;
		}

		size_t capacity() const
		{
			return _capacity;
		}

		//调整空间大小
		void resize(size_t n, char ch = '\0')
		{
			if (n > _size && n <= _capacity)  //容量不变
			{
				while (_size <= n)
				{
					_str[_size++] = ch;
				}
				_str[_size] = '\0';
			}
			else if (n > _capacity)  //增容
			{
				reserve(n);
				while (_size < n)
				{
					_str[_size++] = ch;
				}
				_str[_size] = '\0';
			}
			else
			{
				_size = n;
				_str[_size] = '\0';
			}
		}

		//预留空间
		void reserve(size_t capacity)
		{
			_capacity = capacity;
			char* tmp = new char[_capacity + 1];
			strcpy(tmp, _str);
			delete[] _str;
			_str = tmp;
		}

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

		bool empty() const
		{
			return _size == 0;
		}

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

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

		void push_back(char c)
		{
			if (_size == _capacity)
			{
				size_t newcapacity = _capacity == 0 ? 5 : _capacity * 2;
				reserve(newcapacity);
			}
			_str[_size++] = c;
			_str[_size] = '\0';
		}

		//尾插一个字符串
		void append(const char* str)
		{
			int len = strlen(str);
			if (_size + len > _capacity)
			{
				reserve(_size + len);
			}
			strcpy(_str + _size, str);
			_size += len;
		}

		//+=一个字符
		string& operator+=(char c)
		{
			push_back(c);
			return *this;
		}

		//+=一个字符串
		string& operator+=(const char* str)
		{
			append(str);
			return *this;
		}

		//插入一个字符
		string& insert(size_t pos, char c)
		{
			assert(pos >= 0 && pos <= _size);
			if (_size + 1 > _capacity)
			{
				size_t newcapacity = _capacity == 0 ? 5 : _capacity * 2;
				reserve(newcapacity);
			}

			size_t end = _size + 1;
			while (end > pos)
			{
				_str[end] = _str[end - 1];
				end--;
			}
			_str[end] = c;
			_size++;
			return *this;
		}

		//插入一个字符串
		string& insert(size_t pos, const char* str)
		{
			assert(pos >= 0 && pos <= _size);
			size_t len = strlen(str);

			if (_size + len > _capacity)
			{
				reserve(_size + len);
			}

			size_t end = _size + 1;
			while (end > pos)
			{
				_str[len + end - 1] = _str[end - 1];
				end--;
			}
			strncpy(_str + pos, str, len);
			_size += len;
			return *this;
		}

		string& erase(size_t pos, size_t n = -1)
		{
			assert(pos >= 0 && pos <= _size);
			if (pos + n >= _size)
			{
				_str[pos] = '\0';
				_size = pos;
			}
			else
			{
				size_t left = pos, right = pos + n;
				while (right <= _size)
				{
					_str[left] = _str[right];
					left++;
					right++;
				}
				_size -= n;
			}
			return *this;
		}

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

		//交换两个字符串
		void swap(string& s)
		{
			std::swap(_str, s._str);
			std::swap(_size, s._size);
			std::swap(_capacity, s._capacity);
		}

		//----------------------------------------String operations-----------------------------//
		const char* c_str() const
		{
			return _str;
		}

		size_t find(char c, size_t pos = 0)
		{
			assert(pos >= 0 && pos <= _size);
			for (size_t i = pos; i < _size; ++i)
			{
				if (_str[i] == c)
					return i;
			}
			return -1;
		}

		size_t rfind(char c, size_t pos = 0)
		{
			assert(pos >= 0 && pos <= _size);
			for (size_t i = _size; i > 0; --i)
			{
				if (_str[i - 1] == c)
					return i;
			}
			return -1;
		}

		size_t find(const char* str, size_t pos = 0)
		{
			assert(pos >= 0 && pos <= _size);
			const char* ptr = strstr(_str + pos, str);
			return ptr == 0 ? -1 : ptr - _str;
		}

		//---------------------------------Non-member function overloads----------------------------//
		friend ostream& operator<<(ostream& out, const string& s);
		friend istream& operator>>(istream& in, string& s);
		friend istream& getline(istream& in, string& s);

	private:
		char* _str;
		size_t _size;
		size_t _capacity;
	};

	//流插入重载
	inline ostream& operator<<(ostream& out, const string& s)
	{
		for (size_t i = 0; i < s._size; ++i)
		{
			out << s._str[i];
		}
		return out;
	}

	//流提取重载
	inline istream& operator>>(istream& in, string& s)
	{
		//char ch = in.get();
		//while (ch != ' ' && ch != '\n')  //cin遇到空格或者换行结束
		//{
		//	s += ch;
		//	ch = in.get();
		//}

		//优化
		char buff[128] = { '\0' };
		size_t i = 0;
		char ch = in.get();
		while (ch != ' ' && ch != '\n')
		{
			if (i == 127)
			{
				s += buff;
				i = 0;
			}
			buff[i++] = ch;
			ch = in.get();
		}

		if (i > 0)
		{
			buff[i] = '\0';
			s += buff;
		}
		return in;
	}

	//读入一行字符
	inline istream& getline(istream& in, string& s)
	{
		char buff[128] = { '\0' };
		size_t i = 0;
		char ch = in.get();
		while (ch != '\n')
		{
			if (i == 127)
			{
				s += buff;
				i = 0;
			}
			buff[i++] = ch;
			ch = in.get();
		}

		if (i > 0)
		{
			buff[i] = '\0';
			s += buff;
		}
		return in;
	}
};

#define _CRT_SECURE_NO_WARNINGS 1

#include "string.h"

void Test_String1()
{
	//构造
	thj::string s1;
	thj::string s2("abcdef");

	//拷贝构造
	thj::string s3 = s2;

	//赋值重载
	s1 = s2;
}

void Test_string2()
{
	thj::string s1("1234");
	thj::string::iterator it = s1.begin();
	for (it; it < s1.end(); ++it)
		(*it)++;
	cout << s1.c_str() << endl;

	const thj::string s2("1234");
	thj::string::iterator it2 = s2.begin();
	for (it2; it2 < s2.end(); ++it2)
		(*it2)++;
	cout << s2.c_str() << endl;
}

void Test_string3()
{
	thj::string s("hello world");
	cout << s.size() << endl;
	cout << s.capacity() << endl;
	cout << s.c_str() << endl;

	//s.resize(5);
	//cout << s.size() << endl;
	//cout << s.capacity() << endl;
	//cout << s.c_str() << endl;

	//s.reserve(15);
	//cout << s.size() << endl;
	//cout << s.capacity() << endl;
	//cout << s.c_str() << endl;

	//s.resize(12, 'x');
	//cout << s.size() << endl;
	//cout << s.capacity() << endl;
	//cout << s.c_str() << endl;

	s.resize(20, 'x');
	cout << s.size() << endl;
	cout << s.capacity() << endl;
	cout << s.c_str() << endl;
}

void Test_string4()
{
	//thj::string s = "hello world";
	//s.push_back('!');
	//cout << s.c_str() << endl;

	//s.append("xxx");
	//cout << s.c_str() << endl;

	//s += "1";
	//cout << s.c_str() << endl;

	//s += "234";
	//cout << s.c_str() << endl;

	//thj::string s1 = "hello w";
	//s1.insert(3, 'x');
	//cout << s1.c_str() << endl;

	//s1.insert(8, 'x');
	//cout << s1.c_str() << endl;

	//s1.insert(0, 'x');
	//cout << s1.c_str() << endl;

	//thj::string s2 = "hello";
	//s2.insert(5, " world");
	//cout << s2.c_str() << endl;

	//s2.insert(2, "xxxxxxxxxxxxxxxxx");
	//cout << s2.c_str() << endl;

	//s2.insert(0, "!!!!!!!!!!");
	//cout << s2.c_str() << endl;

	thj::string s3 = "hello world";
	s3.erase(11, 10);
	cout << s3.c_str() << endl;

	s3.erase(1, 2);
	cout << s3.c_str() << endl;

	s3.erase(0, 4);
	cout << s3.c_str() << endl;
}

void Test_String5()
{
	thj::string s = "abcdefefeeffc";
	cout << s.find('c', 5) << endl;
	cout << s.find('c') << endl;
	cout << s.find("efe") << endl;
	cout << s.find("efe", 5) << endl;
	cout << s.find("efe", 7) << endl;
}

void Test_string6()
{
	thj::string s;
	cin >> s;
	cout << s << endl;

	thj::string s1;
	cin >> s1;
	cout << s1 << endl;

	thj::string s2;
	thj::getline(cin, s2);
	cout << s2 << endl;
}

int main()
{
	//member functions
	//Test_String1();
	//iteratos
	//Test_string2();
	//capacity
	//Test_string3();
	//modify
	//Test_string4();
	//string operations
	//Test_String5();
	//non-mumber function overloads
	Test_string6();

	return 0;
}