pointers - C++ interview about operator -

here code implementing = assignment class named cmystring, , code right.

cmystring& cmystring::operator =(const cmystring &str) {  if(this == &str)      return *this;   delete []m_pdata;  m_pdata = null;   m_pdata = new char[strlen(str.m_pdata) + 1];  strcpy(m_pdata, str.m_pdata);   return *this;  }  

the instance passed reference, , first 'if' checking whether instance passed in or not. question is: why use &str compare, doesn't str contain address of instance? 1 explain how line works?

also, want make sure this contains address of object: correct?

address-of operator , reference operator different.

the & used in c++ reference declarator in addition being address-of operator. meanings not identical.

int target; int &rtarg = target;  // rtarg reference integer.                       // reference initialized refer target. void f(int*& p);      // p reference pointer 

if take address of reference, returns address of target. using previous declarations, &rtarg same memory address &target.