武功高手在异界:一个关于复制构造函数的问题?

#include <iostream>
#include <string.h>
using namespace std;
class String
{
public:
String();
String(const char *const);
String(const String &);
~String();
char & operator[](unsigned short offset);
char operator[](unsigned short offset) const;
String operator+(const String&);
void operator+=(const String&);
String & operator= (const String &);
unsigned short GetLen()const { return itsLen; }
const char * GetString() const { return itsString; }

private:
String (unsigned short); // private constructor
char * itsString;
unsigned short itsLen;
};
String::String()
{
itsString = new char[1];
itsString[0] = '\0';
itsLen=0;
}
String::String(const String & rhs)
{
itsLen=rhs.GetLen();
itsString=new char[itsLen+1];
for(unsigned short i=0;i<itsLen;i++)
itsString[i]=rhs[i];
itsString[itsLen]='\0';
cout<<"the time constructor:"<<endl;
}
String::String(unsigned short len)
{
itsString = new char[len+1];
for (unsigned short i = 0; i<=len; i++)
itsString[i] = '\0';
itsLen=len;
}
String::String(const char * const cString)
{
itsLen = strlen(cString);
itsString = new char[itsLen+1];
for (unsigned short i = 0; i<itsLen; i++)
itsString[i] = cString[i];
itsString[itsLen]='\0';

}
String::~String ()
{
delete [] itsString;
itsLen = 0;
}
String& String::operator=(const String & rhs)
{
if (this == &rhs)
return *this;
delete [] itsString;
itsLen=rhs.GetLen();
itsString = new char[itsLen+1];
for (unsigned short i = 0; i<itsLen;i++)
itsString[i] = rhs[i];
itsString[itsLen] = '\0';
return *this;
}
char & String::operator[](unsigned short offset)
{
if (offset > itsLen)
return itsString[itsLen-1];
else
return itsString[offset];
}
char String::operator[](unsigned short offset) const
{
if (offset > itsLen)
return itsString[itsLen-1];
else
return itsString[offset];
}
String String::operator+(const String& rhs)
{
unsigned short totalLen = itsLen + rhs.GetLen();
String temp(totalLen);
unsigned short i;
for ( i= 0; i<itsLen; i++)
temp[i] = itsString[i];
for (unsigned short j = 0; j<rhs.GetLen(); j++, i++)
temp[i] = rhs[j];
temp[totalLen]='\0';
return temp;
}
void String::operator+=(const String& rhs)
{
unsigned short rhsLen = rhs.GetLen();
unsigned short totalLen = itsLen + rhsLen;
String temp(totalLen);
unsigned short i;
for (i = 0; i<itsLen; i++)
temp[i] = itsString[i];
for (unsigned short j = 0; j<rhs.GetLen(); j++, i++)
temp[i] = rhs[i-itsLen];
temp[totalLen]='\0';
*this = temp;
}