c++ new string数组问题

今天考虑一个问题：

      string *p = new string[5];

      p[0] = "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa";

      p[2] = "bb";

new操作时是需要知道类型的大小的。但new string[5]时怎么知道string的大小的呢？ 感觉很奇怪。

      经过思考，认为原因如下：

      1.  new string[5]会调用string的默认构造函数。所以会有5个空字符串被创建。

       2. string 的=操作会重新new char[], 更新原来的string内部的char*。

       另外，string的实现参考：

#include <iostream>
#include <string.h>
using namespace std;
class MyString
{
	char* m_str;
	int m_nLength;
	void _InitString();
	
public:
	//1. 默认构造函数
	MyString();
	// 2. 带参构造函数
	MyString( unsigned int length, const char& ch );
	MyString(const char* str);
	MyString( const char* str, unsigned int length );
	MyString( const MyString& str, unsigned int index, unsigned int length );
	// 3. 拷贝构造函数
	MyString( const MyString& s );
	//4.析构函数
	~MyString();

	// 5. 追加字符串函数
	MyString& append( const MyString& _str );
	MyString& append( const char* str );
	MyString& append( const MyString& str, unsigned int index, unsigned int len );
	MyString& append( const char* str, unsigned int num );
	MyString& append( unsigned int num, char ch );
	/*
	// 6. 赋值函数
	MyString& assign( const MyString& str );
	MyString& assign( const char* str );
	MyString& assign( const char* str, unsigned int num );
	MyString& assign( const MyString& str, unsigned int index, unsigned int len );
	// 	
	// 7. 返回字符串指针函数
	const char* c_str() const;
	// 8. 字符串比较函数
	int MyString::compare( const MyString& str );
	int compare( const char* str );
	int compare( unsigned int index, unsigned int length, const MyString& str );
	
	// 9. 拷贝函数
	unsigned int copy( char* str, unsigned int num, unsigned int index  );
	
	// 	10. 查找函数
	unsigned int find( const MyString& str, unsigned int index );
	unsigned int find( const char* str, unsigned int index );
	unsigned int find( char ch, unsigned int index );
	
	// 		 11. 替换函数
	void replace(const char* findString, const char* replaceString);
	
	// 12. 返回子串
	MyString substr( unsigned int index, unsigned int num  );
	
	// 	// 13. 交换字符串函数
	void swap(MyString& from );
	
	// 14. 其他函数
	void clear();
	unsigned int length() const;
	unsigned int size() const;
	// 15. 重载运算符
	// 1). 比较运算
	friend bool operator==(const MyString& c1, const MyString& c2);
	friend bool operator!=(const MyString& c1, const MyString& c2);
	// 	
	// 2). 追加运算
	friend MyString operator+(const MyString& s1, const MyString& s2 );
	friend MyString operator+(const char* s, const MyString& s2 );
	// 3). 输入输出运算
	friend ostream& operator<<( ostream& os, const MyString& s );
	friend istream& operator>>( istream& is, MyString& s );
	// 	
	// 4). 赋值运算
	MyString& operator=( const MyString& s );
	MyString& operator=( const char* s );
	char& operator[]( unsigned int index );
	*/
	//显示结果
	void Show()
	{
		cout<<m_str<<endl;
	}
	
};

MyString::MyString()
{
	m_str=new char[1];
	m_str[0]=0;
	int m_nLength=0;
}
MyString::~MyString()
{
	delete []m_str;
	m_str=NULL;
}
MyString::MyString( unsigned int length, const char& ch )
{
	m_nLength=length;
	m_str=new char[m_nLength+1];
	for (int i=0;i<m_nLength;++i)
	{
		m_str[i]=ch;
	}
	m_str[m_nLength]=0;

}
MyString::MyString(const char* str)
{
	if (NULL==str)
	{
		m_str=new char[1];
		m_str[0]=0;
		int m_nLength=0;
	}
	else
	{
		m_str=new char[strlen(str)+1];
		strcpy(m_str,str);
	    m_nLength=strlen(str);
	}
	
}
MyString::MyString( const char* str, unsigned int length )
{
	if (NULL==str)
	{
		m_str=new char[1];
		m_str[0]=0;
		int m_nLength=0;
	}
	else
	{
		m_nLength=length;
		m_str=new char[m_nLength+1];
		strncpy(m_str,str,m_nLength);
		m_str[m_nLength]=0;
	}
}
MyString::MyString( const MyString& str, unsigned int index, unsigned int length )
{
	m_nLength=length;
	m_str=new char[m_nLength+1];
	strncpy(m_str,str.m_str+index,m_nLength);
	m_str[m_nLength]=0;
}
MyString::MyString( const MyString& s )
{
	m_str= new char[strlen(s.m_str)+1];
	strcpy(m_str,s.m_str);
}
/*
MyString::MyString& append( const MyString& _str )
{

}
*/
MyString& MyString::append( const char* str )
{
	if (NULL==str)
	{
		m_str=new char[1];
		m_str[0]=0;		
	}
	else
	{
		strcat(m_str,str);
	}
	return *m_str;
}


MyString& MyString::append( const MyString& _str )
{
	char*p=new char[strlen(m_str)+strlen(_str.m_str)+1];
	strcpy(p,m_str);
	strcat(p,_str.m_str);
    p[strlen(m_str)+strlen(_str.m_str)]=0;
	delete []m_str;
	m_str=p;
	return *this;
}

MyString& MyString::append( const char* str )
{
	char*p=new char[strlen(m_str)+strlen(str)+1];
	strcpy(p,m_str);
	strcat(p,str);
	p[strlen(m_str)+strlen(str)]=0;
	delete []m_str;
	m_str=p ;
	
	return *this;
}
MyString& MyString::append( const MyString& str, unsigned int index, unsigned int len )
{
	char*p=new char[strlen(m_str)+strlen(str.m_str)-index+1];
	strcpy(p,m_str);
	strncat(p,str.m_str+index,len);
	p[strlen(m_str)+strlen(str.m_str)-index]=0;
	delete []m_str;
	m_str=p;
	return *this;
}
MyString& MyString::append( const char* str, unsigned int num )
{
	char*p=new char[num+1];
	strncpy(p,str,num);
   p[num]=0;
	delete []m_str;
	m_str=p;

	return*this;
}
MyString& MyString::append( unsigned int num, char ch )
{
	char*p=new char[num+1];
	for(int i=0;i<num;++i)
	{
		p[i]=ch;
	}
	p[num]=0;
	delete []m_str;
	m_str=p;

	return *this;
}
MyString& MyString::assign( const MyString& str )
{
<span style="color:#FF0000;">	char*p=new char[strlen(str.m_str)+1];
	strcpy(p,str.m_str);
    p[strlen(str.m_str)]=0;
	delete []m_str;
	m_str=p;
	return *this;</span>
}
MyString& MyString::assign( const char* str )
{
	char*p=new char[strlen(str)+1];
	strcpy(p,str);
	p[strlen(str)]=0;
	delete []m_str;
	m_str=p;
	return *this;
}
MyString& MyString::assign( const char* str, unsigned int num )
{
	char*p=new char[num+1];
	strncpy(p,str,num);
	p[num]=0;
	delete []m_str;
	m_str=p;
	return *this;
}
MyString& MyString::assign( const MyString& str, unsigned int index, unsigned int len )
{
	char*p=new char[len+1];
	strncpy(p,str.m_str+index,len);
	p[len]=0;
	delete []m_str;
	m_str=p;
	return *this;
}