C++ string类简单实现

#include<iostream>
#include<cstring>

using namespace std;

class MyString
{
friend ostream &operator<<( ostream &, const MyString & );

public:
MyString(const char *s);
MyString( );
MyString(const MyString &);
~MyString();

MyString &operator +=(const MyString &);
MyString operator +(const MyString &);
MyString &operator = (const MyString &right);
MyString &operator = (const char *);
MyString &operator =(int );

char &operator [](int subscript) ;
int getlength();
char *str;
int length;

};

ostream & operator<<( ostream &os, const MyString &s )
{
os << s.str;
return os;

}

MyString::MyString()
:length(0)
{ cout<<"Default constructtion is called:"<<endl;
str = new char[1];
str[0]='\0';
}

MyString::MyString(const char *s)
:length(strlen(s))
{

cout<<"construct function is called:"<<endl;
str=new char[length+1];
strcpy(str,s);

}

MyString::~MyString()
{ cout<<"Desconstruction is called:"<<endl;
delete []str;
str=NULL;

}

MyString::MyString(const MyString ©)
{
length=copy.length;
strcpy(str,copy.str);

}

MyString & MyString::operator =(const MyString &right)
{
if(this==&right)
return *this;
else
{ delete []str;
str = new char[strlen(right.str)+1];

length=right.length;
strcpy(str,right.str);
return *this;
}
}

MyString &MyString::operator +=(const MyString &right)
{ int newlength = length+right.length;
char *p = new char[newlength+1];
strcpy(p,str);
strcat(p,right.str);
delete [] str;

strcpy(str,p);
length=newlength;
delete [] p;
p=NULL;

cout<<"+= is be called!"<<endl;
return *this;
}

MyString & MyString::operator =(const char *s)
{ char *p = new char[strlen(s)+1];
strcpy(p,s);
delete [] str;
strcpy(str,p);
length=strlen(s);

return *this;
}

MyString MyString::operator +(const MyString &right)
{
MyString p;
delete p.str;

p.str = new char[strlen(str)+strlen(right.str)+1];
p.length=length+right.length;
strcpy(p.str,str);
strcat(p.str,right.str);

return p;

}

MyString & MyString::operator =(int num)
{ char a[30];
itoa(num,a,10);
strcpy(str,a);
length=strlen(a);
return *this;
}

char & MyString::operator [](int subscript)
{
if(subscript > 0 || subscript < strlen(str))
return str[subscript-1];
else
{
cout<<"str:"<<subscript<<"out of range..."<<endl;

}
}

int main()
{
MyString s("xupeng");
MyString p("xjw");
cout<<s.str<<endl;
cout<<s[3]<<endl;
cout<<p.str<<endl;

cout<<s+p<<endl;
cout<<p.str<<endl;

return 0;
}