STRING的底层实现

string.h

cpp 复制代码

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

namespace bittersweet
{
	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]{'\0'}), _size(0), _capacity(0)
		{ }
		string(const char* str)
		{
			_size = strlen(str);
			_capacity = _size;
			_str = new char[_capacity + 1];
			strcpy(_str, str);
		}
		string(const string& s)
		{
			_str = new char[s._capacity+1];
			strcpy(_str, s._str);
			_size = s._size;
			_capacity = s._capacity;
		}
		void swap(string& s)
		{

		}
		string(const string& s)
		{
			string tmp(s._str);
			swap(_str, ._str);
			swap(_size, tmp._size);
			swap(_capacity, tmp._capacity);
		}
		string& operator=(const string& s)
		{
			if (this == &s)
			{
				return *this;
			}
			delete[] _str;
			_str = new char[s._capacity + 1];
			strcpy(_str, s._str);
			_size = s._size;
			_capacity = s._capacity;
			return *this;
		}
		~string()
		{
			delete[] _str;
			_str = nullptr;
			_size = _capacity = 0;
		}
		const char* c_str() const
		{
			return _str;
		}
		void clear()
		{
			_str[0] = '\0';
			_size = 0;
		}
		size_t size() const
		{
			return _size;
		}
		size_t capacity() const
		{
			return _capacity;
		}
		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 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);
		void insert(size_t pos, const char* str);
		void erase(size_t pos, size_t len = npos);
		size_t find(char ch, size_t pos = 0);
		size_t find(const char* str, size_t pos = 0);
		string substr(size_t pos = 0, size_t len = npos);
	private:
		char* _str;
		size_t _size;
		size_t _capacity;
		const static size_t npos;
	};
	const  size_t string::npos = -1;
	ostream& operator<<(ostream& out, const string& s);
	istream& operator>>(istream& in, string& s);
}

string.c

cpp 复制代码

#include"string.h"
namespace bittersweet
{
	void string::reserve(size_t n)
	{
		if (n > _capacity)
		{
			char* tmp = new char[n + 1];
			strcpy(tmp, _str);
			delete[] _str;
			_str = tmp;
			_capacity = n;
		}
	}
	void string::push_back(char ch)
	{
		if (_size == _capacity)
		{
			reserve(_capacity == 0 ? 4 : _capacity * 2);
		}
		_str[_size] = ch;
		++_size;
		_str[_size] = '\0';
	}
	string& string::operator+=(char ch)
	{
		push_back(ch);
		return *this;
	}
	void string::append(const char* str)
	{
		size_t len = strlen(str);
		if (_size + len > _capacity)
		{
			reserve(_size + len > 2 * _capacity ? _size + len : 2 * _capacity);
		}
		strcpy(_str + _size, str);
		_size += len;
	}
	string& string::operator+=(const char* str)
	{
		append(str);
		return *this;
	}
	void string::insert(size_t pos, char ch)
	{
		assert(pos <= _size);
		if (_size == _capacity)
		{
			reserve(_capacity == 0 ? 4 : _capacity * 2);
		}
		size_t end = _size + 1;
		while (end >= (int)pos)
		{
			_str[end + 1] = _str[end];
			--end;
		}
		_str[pos] = ch;
		++_size;
	}
	void string::insert(size_t pos, const char* str)
	{
		assert(pos <= _size);
		size_t len = strlen(str);
		if (len == 0)
			return;
		if (_size + len > _capacity)
		{
			reserve(_size + len > 2 * _capacity ? _size + len : 2 * _capacity);
		}
		size_t end = _size + len;
		while (end >= pos+len)
		{
			_str[end] = _str[end - len];
			end--;
		}
		for (size_t i = 0; i < len; i++)
		{
			_str[pos + i] = str[i];
		}
		_size += len;
	}
	void string::erase(size_t pos, size_t len )
	//缺省参数只能在声明的时候给，不能在定义的时候给
	{
		if (len >= _size - pos)
		{
			_str[pos] = '\0';
			_size = pos;
		}
		else
		{
			for (size_t i = pos + len; i <= _size; i++)
			{
				_str[i - len] = _str[i];
			}
			_size -= len;
		}
	}
	size_t string::find(char ch, size_t pos)
	{
		assert(pos < _size);
		for (size_t i = pos; i < _size; i++)
		{
			if (_str[i] == ch)
				return i;
		}
		return npos;
	}
	size_t string::find(const char* str, size_t pos )
	{
		assert(pos < _size);

		const char* ptr = strstr(_str+pos, str);
		if (ptr == nullptr)
		{
			return npos;
		}
		else
		{
			return ptr - _str;
		}
	}
	string string::substr(size_t pos, size_t len)
	{
		assert(pos < _size);
		if (len > _size)
		{
			len = _size - pos;
		}
		string sub;
		sub.reserve(len);
		for (size_t i = 0; i < len;i++)
		{
			sub += _str[pos + i];
		}
		return sub;
	}
	ostream& operator<<(ostream& out, const string& s)
	{
		for (auto ch : s)
		{
			out << ch;
		}
		return out;
	}
	istream& operator<<(istream& in, string& s)
	{
		s.clear();
		char ch;
		ch = in.get();
		while (ch != ' ' && ch != '\n')
		{
			s += ch;

			ch = in.get();
		}
		return in;
	}
}