Changing namespaces

[Blue Ocean]

Forgive me for asking so many questions so quickly. I am simply
asking as they come up unanswered in my book.

Can you change namespaces half way through a file? For instance, if
you want to use std and then half way through switch to your own:
{
...
using namespace std;
cout << "doing polygons";
using namespace polygon;
cout << poly1;
...
}

I know that this is a ridiculous example. Why would anyone define an
outstream for a 3D object with the name cout. But, suppose they did,
would this code snippet work, or do you have to use just one namespace
per file and be explicit about the use of other namespaces?

[John Harrison]

"Andre Kostur" <nn******@kostu r.net> wrote in message
news:Xn******** *************** ********@207.35 .177.134...

"Sharad Kala" <no************ ******@yahoo.co m> wrote in
news:2l******** ****@uni-berlin.de:

"John Harrison" <jo************ *@hotmail.com> wrote in message
news:opsas0q1jt 212331@andronic us...

On Thu, 08 Jul 2004 05:32:45 GMT, Russell Hanneken <[e-mail] >
wrote:

> John Harrison wrote:
>> On Wed, 07 Jul 2004 22:20:42 GMT, Russell Hanneken
>> <[e-mail] >

[snip]

I think I'm really going to have to look this up in the standard,
which is always a scary prospect. But here's a guess, your version of
the code injects all the std namespace names into the scope of main,
but ::string ignores any names within the scope of main and just
looks directly at the global scope. I could be utterly wrong.

I think you are right.
Section 3.4.3/4
A name prefixed by the unary scope operator :: (5.1) is looked up in
global scope, in the translation unit where it is used. The name shall
be declared in global namespace scope or shall be a name whose
declaration is visible in global scope because of a using-directive
(3.4.3.2). The use of :: allows a global name to be referred to even
if its identifier has been hidden (3.3.7).

I stand corrected. Personally it seems kinda weird, but thems the
breaks. I wonder why the decision was made that using the "::" scope
operation still goes through the "search path"... I would have figured
that by saying "::" you _meant_ global only...

Isn't the point is that there isn't a search path? Once you use 'using
namespace xxx;' within the global namespace all the names in xxx *are*
global.

john

[Andre Kostur]

"John Harrison" <jo************ *@hotmail.com> wrote in
news:2l******** ****@uni-berlin.de:

"Andre Kostur" <nn******@kostu r.net> wrote in message
news:Xn******** *************** ********@207.35 .177.134...

"Sharad Kala" <no************ ******@yahoo.co m> wrote in
news:2l******** ****@uni-berlin.de:

>
> "John Harrison" <jo************ *@hotmail.com> wrote in message
> news:opsas0q1jt 212331@andronic us...
>> On Thu, 08 Jul 2004 05:32:45 GMT, Russell Hanneken <[e-mail] >
>> wrote:
>>
>> > John Harrison wrote:
>> >> On Wed, 07 Jul 2004 22:20:42 GMT, Russell Hanneken
>> >> <[e-mail] >
> [snip]
>>
>> I think I'm really going to have to look this up in the standard,
>> which is always a scary prospect. But here's a guess, your version of >> the code injects all the std namespace names into the scope of main, >> but ::string ignores any names within the scope of main and just
>> looks directly at the global scope. I could be utterly wrong.
>>
>
> I think you are right.
> Section 3.4.3/4
> A name prefixed by the unary scope operator :: (5.1) is looked up in
> global scope, in the translation unit where it is used. The name shall > be declared in global namespace scope or shall be a name whose
> declaration is visible in global scope because of a using-directive
> (3.4.3.2). The use of :: allows a global name to be referred to even
> if its identifier has been hidden (3.3.7).

I stand corrected. Personally it seems kinda weird, but thems the
breaks. I wonder why the decision was made that using the "::" scope
operation still goes through the "search path"... I would have figured
that by saying "::" you _meant_ global only...

Isn't the point is that there isn't a search path? Once you use 'using
namespace xxx;' within the global namespace all the names in xxx *are*
global.

I would have figured that the "search path" would be used for unqualified
names. Much like specifying an executable in Windows or Unix. Just type
the name, and it searches $PATH for the executable. But if you specify a
full pathname to the file (like /program), then you mean just the
executable in the root directory and no other.