copy constructors; why can access private data?

[thomas]

guys, I defined a copy constructor like this.

--code--
FiveTuple::FiveTuple(const FiveTuple &fv_tuple){
source_ip_ = fv_tuple.source_ip_;
dest_ip_ = fv_tuple.dest_ip_;
source_port_ = fv_tuple.source_port_;
dest_port_ = fv_tuple.dest_port_;
ip_protocol_ = fv_tuple.ip_protocol_;
}
--code--

It works.

but the source_ip_, dest_ip_, etc are all private;
How can the copy constructor access private data of fv_tuple directly?

 

[Alf P. Steinbach]

* thomas:

guys, I defined a copy constructor like this.

--code--
FiveTuple::FiveTuple(const FiveTuple &fv_tuple){
source_ip_ = fv_tuple.source_ip_;
dest_ip_ = fv_tuple.dest_ip_;
source_port_ = fv_tuple.source_port_;
dest_port_ = fv_tuple.dest_port_;
ip_protocol_ = fv_tuple.ip_protocol_;
}

You should use a memory initializer list in order to support future
class-type IP addresses, and since apparently this copy constructor does
nothing more or less than the compiler-generated one would do, you
shouldn't really define it in the first place.

--code--

It works.

but the source_ip_, dest_ip_, etc are all private;
How can the copy constructor access private data of fv_tuple directly?

It's a (special) member function.

Member functions have access to private instance data of instances of
the class they're member functions of.


Cheers, & hth.,

- Alf

 

[Jeff Schwab]

guys, I defined a copy constructor like this.

--code--
FiveTuple::FiveTuple(const FiveTuple &fv_tuple){
source_ip_ = fv_tuple.source_ip_;
dest_ip_ = fv_tuple.dest_ip_;
source_port_ = fv_tuple.source_port_;
dest_port_ = fv_tuple.dest_port_;
ip_protocol_ = fv_tuple.ip_protocol_;
}
--code--

It works.

but the source_ip_, dest_ip_, etc are all private;
How can the copy constructor access private data of fv_tuple directly?

Private to the type, not the object.

 

[Martin York]

guys, I defined a copy constructor like this.

--code--
FiveTuple::FiveTuple(const FiveTuple &fv_tuple){
source_ip_ = fv_tuple.source_ip_;
dest_ip_ = fv_tuple.dest_ip_;
source_port_ = fv_tuple.source_port_;
dest_port_ = fv_tuple.dest_port_;
ip_protocol_ = fv_tuple.ip_protocol_;}

--code--

It works.

but the source_ip_, dest_ip_, etc are all private;
How can the copy constructor access private data of fv_tuple directly?

A class is a friend of itself.
Thus one object of class X is able to access the private members of
another object of class X.