string的模拟实现

#pragma once
#include<iostream>
#include<assert.h>
namespace Z {
	class string {
	public:
		


		string(const char* str="");//""就是\0的意思

		~string();
		}

#define  _CRT_SECURE_NO_WARNINGS 1
#include"string.h"
namespace Z {

	//string::string()
	//	:_size(0)
	//	, _capacity(0)
	//	, _str(new char [1] {'\0'})
	//{

	//}
	string::string(const char* str)
		:_size(strlen(str))//都用模板的话要和定义顺序对齐，所以这里只使用一个模板
	{
		_capacity = _size;
		_str = new char[_size + 1];//永远多开一个空间要存'\0'
		strcpy(_str, str);
	}
	string::~string() {
		delete[]_str;
		_str = nullptr;
		_size = 0;
		_capacity = 0;


	}

void string::reserve(int n)
{
	if (n > _capacity) {
		char* tmp = new char[n + 1];//多开一个放'\0'
		strcpy(tmp, _str);
		delete(_str);
		_str = tmp;
		_capacity = n;



	}



}

void string::push_back(char ch) {
	if (_size == _capacity) {
		reserve(_capacity==0?4:_size * 2);
	}
	_str[_size] = ch;
	_size++;
	

}
void string::append(const char* str) {
	int newcapacity;
	if (_size + strlen(str) > _capacity) {
		 newcapacity = _capacity * 2;



	}
	if (newcapacity < _size + strlen(str)) {
		newcapacity = _size + strlen(str);
	}
	reserve(newcapacity);
	strcpy(_str + _size, str);
	_size = _size + strlen(str);
}

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

		append(str);
		return *this;
	}

char& operator[](size_t i) {
	assert(i < _size);
		return _str[i];


}

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


	}

		//迭代器的遍历
		iterator begin() {
			return _str;
		}
		iterator end() {
			return _str+_size;
		}
		const reverse_iterator begin()const {
			return _str;
		}
		const reverse_iterator end()const {
			return _str + _size;
		}