class - How does return by reference work in C++ classes? -

in c++, if type:

int x=5; int &y=x; 

then y act alias memory location original x stored , can proven/tested printing memory location of both, x , y

the output of similar program below:

x @ location: 0x23fe14 y @ location: 0x23fe14 

but classes?

when member function declared return type reference , function uses this pointer, function returning?

for example:

#include <iostream> class simple {     int data; public:     // ctor     simple():         data(0)         {}      // getter function     int& getter_data()     {   return this->data;    }      // modifier functions     simple& add(int x=5)     {   this->data += x;         return *this;     }     simple& sub(int x=5)     {   this->data -= x;         return *this;     } };  int main() {   simple obj;     obj.add().sub(4);  ////////// how & why working? /////////     std::cout<<obj.getter_data();     getchar(); } 

why possible execute command in highlighted line?

what kind of data obj.add() returning sub()?

when member-function returns simple& initialized *this (*this being instance of simple) semantics same own "reference example"; reference initialized instance of type.

you initializing returned reference object itself.

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the below snippets semantically equivalent:

obj.add ().sub (4); 

simple& ref = obj.add ();  ref.sub (4); // `ref` `obj`,              // address of `ref` , `obj` same