Picking const vs. non-const member functions upon a call

[cheeser]

Hello all,

Please see the question in the code below...

Thanks!
Dave
#include <iostream>

using namespace std;

class foo
{
public:
foo(int d) : data(d) {}
void print() const {cout << "const" << endl;}
void print() {cout << "non-const" << endl;}

private:
int data;
};

int main()
{
foo a(42);

// The call below calls the non-const print();
// I want the const print() to be called!
// a.print();

// Here's one way to do it. Is there a more elegant way?
// Making a const is not within the scope of my question!
static_cast<con st foo>(a).print() ;

return 0;
}

[John Carson]

"cheeser" <ch**********@y ahoo.com> wrote in message
news:vo******** ****@news.super news.com

Mike, Jonathan and Robert,

I merely wanted to verify that it is not possible (without
undesirable casts or other things of that ilk) to invoke a const
method from a non-const object if there is also a non-const method of
the same name. I do not have a specific application at hand; I just
wanted confirmation that my understnading that it can't be done is
correct. You have provided that confirmation. For this I offer my
thanks.

A good evening to all,
Dave

Same name yes, if the arguments can differ.

class foo
{
public:
foo(int d) : data(d) {}
void print(int a=0) const {cout << "const" << endl;}
void print() {cout << "non-const" << endl;}
private:
int data;
};
int main()
{
foo a(42);
const foo b(43);

a.print(); // non-const
a.print(0); // const
b.print(); // const
return 0;
}
--
John Carson
1. To reply to email address, remove donald
2. Don't reply to email address (post here instead)

[Kevin Goodsell]

cheeser wrote:

// The call below calls the non-const print();
// I want the const print() to be called!
// a.print();

// Here's one way to do it. Is there a more elegant way?
// Making a const is not within the scope of my question!
static_cast<con st foo>(a).print() ;

Here's an alternative, but I don't know if I'd consider it any more elegant:

const foo &ca = a;
ca.print();

I believe that will do what you are asking.

-Kevin
--
My email address is valid, but changes periodically.
To contact me please use the address from a recent posting.

[Gianni Mariani]

John Carson wrote:

"cheeser" <ch**********@y ahoo.com> wrote in message
news:vo******** ****@news.super news.com

Mike, Jonathan and Robert,

I merely wanted to verify that it is not possible (without
undesirable casts or other things of that ilk) to invoke a const
method from a non-const object if there is also a non-const method of
the same name.

Here are a couple of other suggestions.

class foo
{
public:
foo(int d) : data(d) {}
void print() const {cout << "const" << endl;}
void print() {cout << "non-const" << endl;}
void cprint() const { print(); }
private:
int data;
};
int main()
{
foo a(42);
const foo & b(a);

a.print(); // non-const
b.print(); // const
a.cprint(); // const
return 0;
}

[cheeser]

"Kevin Goodsell" <us************ *********@never box.com> wrote in message
news:ie******** ********@newsre ad4.news.pas.ea rthlink.net...

cheeser wrote:

// The call below calls the non-const print();
// I want the const print() to be called!
// a.print();

// Here's one way to do it. Is there a more elegant way?
// Making a const is not within the scope of my question!
static_cast<con st foo>(a).print() ;

Here's an alternative, but I don't know if I'd consider it any more

elegant:
const foo &ca = a;
ca.print();

I believe that will do what you are asking.

-Kevin
--
My email address is valid, but changes periodically.
To contact me please use the address from a recent posting.

Ahh, there it is! I had a feeling there had to be a way, but my mind just
didn't get on the right track... Thanks man...

[Jerry Coffin]

In article <vo************ @news.supernews .com>, ch**********@ya hoo.com
says...

[ ... ]

// The call below calls the non-const print();
// I want the const print() to be called!
First of all, if you care much about this, it's probably a good clue
that your design has major problems.
// a.print();

// Here's one way to do it. Is there a more elegant way?
// Making a const is not within the scope of my question!
static_cast<con st foo>(a).print() ;

You have (at least) a few other choices, such as temporarily creating a
reference to a const object, but they all come out the same. If a
member function is overloaded based on const-ness, then the const
overload should only be selected when you invoke it on (a reference or
pointer to) a const object. Therefore, if you want to invoke the const
member function, you need to treat the object as const, either through a
cast (as you've already mentioned) or by referring to the object via a
pointer or reference to const.

--
Later,
Jerry.

The universe is a figment of its own imagination.

[jeffc]

"cheeser" <ch**********@y ahoo.com> wrote in message
news:vo******** ****@news.super news.com...

#include <iostream>

using namespace std;

class foo
{
public:
foo(int d) : data(d) {}
void print() const {cout << "const" << endl;}
void print() {cout << "non-const" << endl;}

private:
int data;
};

int main()
{
foo a(42);

// The call below calls the non-const print();
// I want the const print() to be called!
// a.print();

// Here's one way to do it. Is there a more elegant way?
// Making a const is not within the scope of my question!
static_cast<con st foo>(a).print() ;

I don't know what the "scope" of your question is, but the obvious answer to
me would be to define
const foo a(42);
But if that's not what you want, I think you should question if you really
want a const and non-const version of the same function.

[jeffc]

"Jonathan Mcdougall" <jo************ ***@DELyahoo.ca > wrote in message
news:N6******** ************@we ber.videotron.n et...

My question was : why do you want that? Perhaps we could find
another way. Post some real code with your real design with
some real problems.

Why are you guys badgering this guy? He already said there is no point
other than knowing whether or not it can be done.

[cpp_weenie]

"Kevin Goodsell" <us************ *********@never box.com> wrote in message
news:ie******** ********@newsre ad4.news.pas.ea rthlink.net...

cheeser wrote:

// The call below calls the non-const print();
// I want the const print() to be called!
// a.print();

// Here's one way to do it. Is there a more elegant way?
// Making a const is not within the scope of my question!
static_cast<con st foo>(a).print() ;

Here's an alternative, but I don't know if I'd consider it any more

elegant:
const foo &ca = a;
ca.print();

I believe that will do what you are asking.

-Kevin
--
My email address is valid, but changes periodically.
To contact me please use the address from a recent posting.

In fact, here's the full extent of possibilities:

#include <iostream>

using namespace std;

class foo
{
public:
void bar() {cout << "bar()" << endl;}
void bar() const {cout << "bar() const " << endl;}
void bar() volatile {cout << "bar() volatile" << endl;}
void bar() const volatile {cout << "bar() const volatile" << endl;}
};

int main()
{
foo p;
const foo &c = p;
volatile foo &v = p;
const volatile foo &cv = p;

p.bar();
c.bar();
v.bar();
cv.bar();

return 0;
}