Friends and Namespaces

[Simon]

Hi,

I have a class Foo which defines a friend function Bar. When I place the Bar
function within a namespace, I can no longer access the Foo private data
(i'm guessing it is not recognised as a friend). Could someone explain this
behaviour, as i'm obviously not understanding namespaces properly.

Thanks for your help,
Simon ;o)

//---------------

#include <iostream>

class Foo {
public:
Foo() { foo_int = 101; }
private:
int foo_int;
friend Bar(const Foo& f);
};

namespace mynamespace {
int Bar(const Foo& f) {
return f.foo_int;
}
}

int main() {
Foo f;
std::cout << mynamespace::Bar(f);
return 0;
}

 

[WW]

Hi,

I have a class Foo which defines a friend function Bar. When I place
the Bar function within a namespace, I can no longer access the Foo
private data (i'm guessing it is not recognised as a friend). Could
someone explain this behaviour, as i'm obviously not understanding
namespaces properly. [SNIP]
class Foo {
public:
Foo() { foo_int = 101; }
private:
int foo_int;
friend Bar(const Foo& f);

friend mynamespace::Bar(const Foo& f);

};

namespace mynamespace {
int Bar(const Foo& f) {

[SNIP]

Bar is not called Bar anymore. It is mynamespace::Bar. With your original
libe you gave friendship to a function called Bar, in the global namespace.

 

[tom_usenet]

Hi,

I have a class Foo which defines a friend function Bar. When I place the Bar
function within a namespace, I can no longer access the Foo private data
(i'm guessing it is not recognised as a friend). Could someone explain this
behaviour, as i'm obviously not understanding namespaces properly.

You have to declare friendship to the function in the namespace, not
to a non-existent global one.

Thanks for your help,
Simon ;o)

//---------------

#include <iostream>

class Foo;

namespace mynamespace {
int Bar(const Foo& f);
}

class Foo {
public:
Foo() { foo_int = 101; }
private:
int foo_int;
friend Bar(const Foo& f);

friend mynamespace::Bar(const Foo& f);

};

namespace mynamespace {
int Bar(const Foo& f) {
return f.foo_int;
}
}

int main() {
Foo f;
std::cout << mynamespace::Bar(f);
return 0;
}

Tom

 

[Jonathan Mcdougall]

I have a class Foo which defines a friend function Bar. When I place

friend mynamespace::Bar(const Foo& f);

Just to be accurate, you'll get a bunch of errors since
1) mynamespace is undeclared at this point
2) the Bar declaration has no return value

class Foo;

namespace mynamespace
{
int Bar(const Foo& f);
}

class Foo
{
..
friend int mynamespace::Bar(const Foo &f);
};

...


Jonathan