How to hide class member variable

[Marco Segurini]

Hi,

I have a class with some member-functions. I should like to have a way
to add a non-static-member-variabile to the class that be visible by
only one member function.

TIA
Marco.

[Alf P. Steinbach]

* Marco Segurini:

I have a class with some member-functions. I should like to have a way
to add a non-static-member-variabile to the class that be visible by
only one member function.

C++ doesn't directly support that. You can make that member function its
own class that you inherit from, but passing all necessary information up
the chain might entail some run-time inefficiency. Also, it's a lot of
complication for very little gain.

On the other hand, a solution somewhat like that can (just can) be good
medicine for 'mutable'.

And also for resolving e.g. order-of-initialization. It's a very common,
what should I say, meta-pattern. Try it, and if you don't like the result
(I'm sure that I wouldn't, for your case), then just accept the language as
it is, and/or consider _redesigning_ your class.

--
A: Because it messes up the order in which people normally read text.
Q: Why is it such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on usenet and in e-mail?

[Julián Albo]

Marco Segurini wrote:

I have a class with some member-functions. I should like to have a way
to add a non-static-member-variabile to the class that be visible by
only one member function.

Write a class with that variable as private member, put the function in it,
and inherit form him.

--
Salu2

[Isaque]

You can also create a variable private to the function.

class X
{
void fx();
}

void X::fx()
{
int i;
}

if you want to keep its value among calls you should create it as
static.

[John Carson]

"Isaque" <ig******@gmail.com> wrote in message
news:11**********************@g44g2000cwa.googlegr oups.com

You can also create a variable private to the function.

class X
{
void fx();
}

void X::fx()
{
int i;
}

if you want to keep its value among calls you should create it as
static.

The problem with this is that there is only one instance of the variable per
class. Presumably the OP wants one instance per object.
--
John Carson

[red floyd]

John Carson wrote:

"Isaque" <ig******@gmail.com> wrote in message
news:11**********************@g44g2000cwa.googlegr oups.com

You can also create a variable private to the function.

class X
{
void fx();
}

void X::fx()
{
int i;
}

if you want to keep its value among calls you should create it as
static.

The problem with this is that there is only one instance of the variable
per class. Presumably the OP wants one instance per object.

How about:

class X
{
private:
class Y
{
private:
int i;
friend void X::foo();
} y;

public:
void foo();
void bar();
};

void X::foo()
{
// use y.i here safely;

}

void X::bar()
{
// can't use y.i here
}

[John Carson]

"red floyd" <no*****@here.dude> wrote in message
news:uX*****************@newssvr12.news.prodigy.co m

How about:

class X
{
private:
class Y
{
private:
int i;
friend void X::foo();
} y;

public:
void foo();
void bar();
};

void X::foo()
{
// use y.i here safely;

}

void X::bar()
{
// can't use y.i here
}

Looks good to me except that the declaration of foo() needs to precede that
of class Y in order for the code to compile.

--
John Carson