visual c++ - Operator= overloading in C++ -

The C ++ primer book has a code for the C-style character array, and shows how

= article 15.3 operator = in the operator.

  string & amp; String :: operator = (Const four * sobj) {// sobj is an empty pointer, if (! Sobj) {_size = 0; Remove [] _string; _string = 0; } And {_size = strlen (sobj); Remove [] _string; _string = new four [_size + 1]; Streakpie (_string, SOBJ); } Return * This; }   
 Now I would like to know that any reference  string & amp;  Why is it necessary to return,  
  zero string :: operator = (const char * sobj) {// sobj is an empty indicator, if (! Sobj) {_size = 0 ; Remove [] _string; _string = 0; } And {_size = strlen (sobj); Remove [] _string; _string = new four [_size + 1]; Streakpie (_string, SOBJ); }}   
 
 Please help.    
 
 
 It supports the following idioms:  
  String A, B; Const char * c; // Set some interesting a = b = c;   
 To work for this, a proper object or context must be returned to assign  b = c  to  a  ; It is actually  a = (b = c)  according to the C ++ operator priority rules.  
 If you take back the pointer  this , then you have to write  a = * (b = c) , which does not mean the desired meaning.