constructor, copy constructor, and destructor for class string

The prototype of the String class is as follows

Class String
{
Public
String (const char *str=null); constructor function
String (const string &other); Copy constructor
~string (void); Destructors
string& operator= (const String &other); equals operator overloading

Showstring ();

Private
Char *m_data; Pointer
};

String::~string ()
{
    delete [] m_data;//destructor, release address space
}
string::string (const Char *str)
{
    if (str==null)//When the initialization string does not exist, request a space for the m_data to hold ' n ';
      {
        m_data=new char[1];
        *m_data= ' + ';
    }
    else//When the initialization string exists, for m_data to apply the same size space to store the string;
     {
         int Length=strlen (str);
        m_data=new char[length+1];
        strcpy (M_DATA,STR);
    }
}

string::string (const String &other)//copy constructor, function similar to constructor function.
{
int Length=strlen (other.m_data);
M_data=new [length+1];
strcpy (M_data,other.m_data);
}
string& String::operator = (const String &other)
{
if (this==&other)//When the address is the same, return directly;
return *this;

Delete [] m_data;//when the address is not the same, delete the original application of space, re-start construction;

int length= strlen (other.m_data);
M_data=new [length+1];
strcpy (M_data,other.m_data);

return *this;
}

String::showstring ()//Because M_data is a private member, the object can only be accessed through the public member function;

{

cout<<this->m_data<<endl;

}

Main ()
{
String AD;
char * p= "ABCDE";
String B (P);
AD. Showstring ();
Ad=b;
AD. Showstring ();

}

1. The Strcopy function can be a standard library function char *strcpy (char *dest, const char *SRC);

Need #inculde <string.h>

2. Reference Connection:

High quality C++c Programming Guide http://man.chinaunix.net/develop/c&c++/c/c.htm

String function http://www.ggv.com.cn/forum/clib/string/strcpy.html

constructor, copy constructor, and destructor for class string