运算符重载自赋值

Question

can anyone please explain the below function.

  AddressBook& operator =(const AddressBook& bok);///add this two to your struct
    bool operator ==(const AddressBook& bok);///

/***************************************************************************************/
    ///anywhere outside main add this definitions

    bool AddressBook::operator ==(const AddressBook& bok)
    {
        return (firstname==bok.firstname&&lastname==bok.lastname&&addr==bok.addr&&phone==bok.phone);
    }

    AddressBook& AddressBook::operator=(const AddressBook& bok)
    {
        if(*this==bok)
            return *this;
        else
        {
            firstname=bok.firstname;
            lastname=bok.lastname;
            addr=bok.addr;
            phone=bok.phone;
        }
         return *this;
    }

Answer 1

There are two functions here. Both of them overloading operators .
The comparison operator for equality operator== will in this case compare two objects of type AddressBook . It will return true (saying two addressbook objects are equal) when they match in firstname , lastname , addr and phone .
The assignment operator will allow you to assign an AddressBook object to another, and it will copy over the values.

if (*this = bok)
    return *this;

in this case checks if you assign an object to itself. In a class this pointy to the instance of the object. In this case the left hand side of the = operator. If they are the same (Meaning their address in memory is the same), then nothing is copied.
The = operator returns the value assigned. That is why things like

a = b = 7;

are valid. b = 7 assigns 7 to b. The operator returns the value 7. Then that return of 7 is assigned to a. The return value of that operation is discarded.
It is also the unfortunate reason why things like

int a = 5, b = 7;
if(a = b) // assignment, not comparison!
{ /*Do things*/ }

are valid. a is assigned the value of b , the return of the assignment-operation (the value of b , 7) is then used as the condition, which evaluates true. Even if you do want such a thing, it is bad style and should be written in two lines.
All operators in c and c++ are function calls.