[C++STL]C++实现string容器

代码如下:

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

class String
{
public:
	String(const char *str = "")
	{
		assert(str != nullptr);
		_size = strlen(str);
		_str = new char[_size + 1];
		_capacity = _size;
		strcpy(_str, str);
	}

	String(const String &s) :_str(nullptr), _size(0), _capacity(0)
	{
		String tmp(s._str);
		Swap(tmp);
	}

	void Swap(String &s)
	{
		swap(_str, s._str);
		swap(_size, s._size);
		swap(_capacity, s._capacity);
	}

	String &operator=(String s)
	{
		if (this != &s)
		{
			Swap(s);
		}
		return *this;
	}

	~String()
	{
		if (_str != nullptr)
		{
			delete[]_str;
			_str = nullptr;
		}
	}

	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];
	}

	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;
	}

	void reserve(size_t n)
	{
		if (n > _capacity)
		{
			char *tmp = new char[n + 1];
			strcpy(tmp, _str);
			delete[] _str;
			_str = tmp;
			_capacity = n;
		}
	}

	void push_back(const char &ch)
	{
		if (_size == _capacity)
		{
			size_t newCapcity = _capacity == 0 ? 15 : 2 * _capacity;
			reserve(newCapcity);
		}
		_str[_size++] = ch;
		_str[_size] = '\0';
	}

	void resize(size_t n, const char &ch = '\0')
	{
		if (n > _capacity)
		{
			reserve(n);
		}

		if (n > _size)
			memset(_str + _size, ch, (n - _size) * sizeof(char));

		_size = n;
		_str[_size] = '\0';
	}

	void append(const char *str)
	{
		int len = strlen(str);
		if (_size + len > _capacity)
		{
			reserve(_size + len);
		}
		memcpy(_str + _size, str, sizeof(char)*len);

		_size += len;
		_str[_size] = '\0';
	}

	String &operator+=(const String &str)
	{
		append(str._str);
		return *this;
	}

	String &operator+=(const char *str)
	{
		append(str);
		return *this;
	}

	String &operator+=(const char ch)
	{
		push_back(ch);
		return *this;
	}

	void insert(size_t pos, const char &ch)
	{
		assert(pos <= _size);
		if (_size == _capacity)
		{
			size_t newCapacity = _capacity == 0 ? 15 : 2 * _capacity;
			reserve(newCapacity);
		}

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

		_str[pos] = ch;
		++_size;
	}

	void insert(size_t pos, const char *str)
	{
		assert(pos <= _size);
		int len = strlen(str);
		if (_size + len >= _capacity)
		{
			reserve(_size + len);
		}
		size_t end = _size + len;
		while (end > pos + len - 1)
		{
			_str[end] = _str[end - len];
			--end;
		}
		memcpy(_str + pos, str, sizeof(char)*len);
		_size += len;
	}

	void erase(size_t pos, size_t len)
	{
		assert(pos < _size);
		if (pos + len >= _size)
		{
			_size = pos;
			_str[_size] = '\0';
		}
		else
		{
			size_t start = pos + len;
			while (start <= _size)
			{
				_str[pos++] = _str[start];
				++start;
			}
			_size -= len;
		}
	}

	size_t find(const char &ch, size_t pos = 0)
	{
		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 = 0)
	{
		char *ptr = strstr(_str, str);
		if (ptr != nullptr)
		{
			return ptr - _str;
		}
		return npos;
	}


private:
	char *_str;
	size_t _size;
	size_t _capacity;
	static const size_t npos;
};

const size_t String::npos = -1;

String  operator+(const String &str1, const String &str2)
{
	String tmp = str1;
	tmp += str2;
	return tmp;
}

String  operator+(const String &str1, const char *str2)
{
	String tmp = str1;
	tmp += str2;
	return tmp;
}

String operator+(const char &ch, const String &str1)
{
	String tmp = str1;
	tmp += ch;
	return tmp;
}

ostream &operator<<(ostream &out, const String &str)
{
	for (const auto &ch : str)
	{
		cout << ch;
	}
	return out;
}


istream &operator>>(istream &in, String &str)
{
	char ch;
	while (ch = getchar())
	{
		if (ch == ' ' || ch == '\n' || ch == '\t')
		{
			break;
		}
		str += ch;
	}
	return in;
}
           

测试代码如下:

#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include "String.h"
 using namespace std;

int main()
 {
	String str = ("Hello Wecccccccc");
	cout << str << endl;
	String str1 = str;
	cout << str1 << endl;
	for (int i = 0; i < str1.size(); i++)
	{
		cout << str[i] << " ";
	}
	cout << endl;

	for (const auto&ch : str)
	{
		cout << ch << " ";
	}
	cout << endl;

	String::iterator it = str.begin();
	while (it != str.end())
	{
		cout << *it << " ";
		it++;
	}
	cout << endl;
	cout << "str size = " << str.size() << " " << "str capacity = " << str.capacity() << endl;
	str.reserve(20);
	cout << "str size = " << str.size() << " " << "str capacity = " << str.capacity() << endl;

	str.push_back('N');
	str.push_back('N');
	str.push_back('N');
	str.push_back('N');
	str.push_back('N');

	cout << str << endl;

	String str3 = "Weccccc";
	str3.resize(3);
	cout << str3 << endl;
	str3.resize(5, 'a');
	cout << str3 << endl;
	str3.resize(10, 'b');
	cout << str3 << endl;
	str3.append(" hello");
	cout << str3 << endl;

	String str4 = "We";
	String str5 = "cccccccc";
	str4 += str5;
	cout << str4 << endl;
	cout << str4 + str5 << endl;
	String str6;
	str6 = 'W' + str4+"123";
	cout << str6 << endl;


	String str7 = "abc";
	str7.insert(0, '1');
	cout << str7 << endl;
	str7.insert(1, '2');
	cout << str7 << endl;
	str7.insert(5, "35");
	cout << str7 << endl;

	str7.erase(0, 2);
	cout << str7 << endl;
	str7.erase(4, 1);
	cout << str7 << endl;
	str7.erase(1, 2);
	cout << str7 << endl;

	int pos = str7.find('3');
	cout << pos << endl;
	pos = str7.find('b');
	cout << pos << endl;

	return 0;
 }
           

测试结果: