What does *& stand for

[gpraghuram]

Hi ,
In one of the code i saw a declartion like this

virtual void check(Base*& ptr);
 

I cant make out what this *& means and this is ina c++ code
Can somebody throw some light on this
Raghuram

[hariharanmca]

Hi ,
In one of the code i saw a declartion like this

virtual void check(Base*& ptr);
 

I cant make out what this *& means and this is ina c++ code
Can somebody throw some light on this
Raghuram

It may be a Virtual pointer declaration (but i am not sure about that).

[JosAH]

Hi ,
In one of the code i saw a declartion like this

virtual void check(Base*& ptr);
 

I cant make out what this *& means and this is ina c++ code
Can somebody throw some light on this
Raghuram

Base: the type
Base*: a pointer to the type
Base*&: a reference to a pointer of the type
ptr: this is the name of the parameter.

It's a virtual member function with a parameter as decsribed above, and it
doesn't return anything (void).

kind regards,

Jos

[hariharanmca]

Base: the type
Base*: a pointer to the type
Base*&: a reference to a pointer of the type
ptr: this is the name of the parameter.

It's a virtual member function with a parameter as decsribed above, and it
doesn't return anything (void).

kind regards,

Jos

okay, Good to know. But is it possible to explain with any small example?

Thank you.

[gpraghuram]

Base: the type
Base*: a pointer to the type
Base*&: a reference to a pointer of the type
ptr: this is the name of the parameter.

It's a virtual member function with a parameter as decsribed above, and it
doesn't return anything (void).

kind regards,

Jos

I think i shuld have put my question more clearly.
I have doubt only about the *& in the parameter.
How it can be described?

Raghuram

[gsi]

Hi,

It depends on the context used,

1. When used in a lvalue or rvalue context the reference and dereference operator's cancel out each other
eg. *&b = *&a; //same as a=b

2. When used in as a function argument same as above, cancel out each other,
eg, foo(*&a);//function call same as foo(a);

3. When used in as a function parameter, indicates that the pointer argument from a caller is taken in as a reference.

eg, virtual void check(Base*& ptr); // check takes in a Base pointer as a reference.

Thanks,
gsi.

[agvaniya]

I think i shuld have put my question more clearly.
I have doubt only about the *& in the parameter.
How it can be described?

Raghuram

in this context it means that parameter to your function can be treated as a pointer for any given purpose with the added value that any change made to it within function will be reflected outside as well. example:

void f(char*& str) { 
   str = new char[10]; 
   strcpy(str,"hello"); 
}
 
void g() {
   char* my_str = NULL;
   f(my_str);
   cout << my_str << endl;
   delete[] my_str;
}
 

calling g() will print: hello
since the pointer my_str was changed within f()

[JosAH]

I think i shuld have put my question more clearly.
I have doubt only about the *& in the parameter.
How it can be described?

Raghuram

Did you actually *read* my reply? It exactly describes what '*&' means in that
particular context.

kind regards,

Jos

[JosAH]

okay, Good to know. But is it possible to explain with any small example?

Thank you.

Nah, it's just a reference to a pointer instead of a pointer value, call by value vs
call by rereference and all that. The fact that a (reference of) a pointer is passed
doesn't add anything new or interesting to those two parameter passing methods.

kind regards,

Jos

[hariharanmca]

Nah, it's just a reference to a pointer instead of a pointer value, call by value vs
call by rereference and all that. The fact that a (reference of) a pointer is passed
doesn't add anything new or interesting to those two parameter passing methods.

kind regards,

Jos

Just asking to remember my self.
It's okay, But i got it in #7.

[gpraghuram]

Jos,
i understod fully after reading the example.

Thanks jos,agvaniya and gsi for a good explanation.

Thanks a lot
Raghuram

[arunmib]

Hi,

It depends on the context used,

1. When used in a lvalue or rvalue context the reference and dereference operator's cancel out each other
eg. *&b = *&a; //same as a=b

2. When used in as a function argument same as above, cancel out each other,
eg, foo(*&a);//function call same as foo(a);

Thanks,
gsi.

I am sorry, I am not able to follow completely.....Why do I need to do it this way? I mean there must be some purpose or advantage in some particular situation for using this way right... I am kind of lost :-(

[Banfa]

I am sorry, I am not able to follow completely.....Why do I need to do it this way? I mean there must be some purpose or advantage in some particular situation for using this way right... I am kind of lost :-(

You don't need to do it that way most likely wouldn't want to. gsi is was merely giving an example of how the C++ interpreter could interpret those characters if it came across them.

It is a waste of characters and obsfucates (confuses) the code.