c++ string 自己构造string

mystring.h头文件

#pragma once

class MyString
{
private:
	char * m_str;
public:
	MyString();
	MyString(size_t length, char ch);
	MyString(const char * cch);
	MyString(const char * cch, int length);

	const char * c_str() const;
	~MyString();

};

mystring.cpp

#include "mystring.h"
#include <iostream>

MyString::MyString()
{
	m_str = new char('\0');
}

MyString::MyString(size_t length, char ch)
{
	m_str = new char[length + 1];
	for (size_t i = 0; i < length; i++)
		m_str[i] = ch;
	m_str[length] = '\0';
}

MyString::MyString(const char * cch)
{
	size_t length = 0;
	const char *pStr = cch;
	while ('\0' != *pStr)
	{
		length++;
		pStr++;
	}
	m_str = new char[length + 1];
	for (size_t i = 0; i < length; i++)
		m_str[i] = cch[i];
	m_str[length] = '\0';
}

MyString::MyString(const char * cch, int length)
{
	int nlen = 0;
	const char *str = cch;
	while ('\0' != *str)
	{
		nlen++;
		str++;
	}
	nlen = nlen < length ? nlen : length;
	m_str = new char[nlen + 1];
	for (int i = 0; i < nlen; i++)
		m_str[i] = cch[i];
	m_str[nlen] = '\0';
}

const char * MyString::c_str() const
{
	return m_str;
}
MyString::~MyString()
{
	if (NULL != m_str)
	{
		delete [] m_str;
	}		
}