how to generate unique namespaces

[er]

hi,

here's why i'm trying to do:

header1.hpp
namespace{ struct A{};}
struct B1{ A a; };

header2.hpp
namespace{ struct A{};}
struct B2{ A a; };

*.cpp
#include <libs/testing_namespa ce/header1.hpp>
#include <libs/testing_namespa ce/header2.hpp>

header2.hpp|5|e rror: redefinition of ‘struct<unnamed >::A’|

i should expect that because the translation unit includes both
header1 and header 2. so then how can i automatically generate unique
namespaces, one for each of header1 and header2?

thanks.

[Ian Collins]

Re: how to generate unique namespaces

er wrote:

hi,
>
here's why i'm trying to do:
>
header1.hpp
namespace{ struct A{};}
struct B1{ A a; };
>
header2.hpp
namespace{ struct A{};}
struct B2{ A a; };
>
*.cpp
#include <libs/testing_namespa ce/header1.hpp>
#include <libs/testing_namespa ce/header2.hpp>
>
header2.hpp|5|e rror: redefinition of ‘struct<unnamed >::A’|
>
i should expect that because the translation unit includes both
header1 and header 2. so then how can i automatically generate unique
namespaces, one for each of header1 and header2?
>

You can't. If you must, use a code generator.

If you automatically generate unique namespaces, how do you use them?

--
Ian Collins.

[er]

Re: how to generate unique namespaces

On Sep 17, 11:04 pm, Ian Collins <ian-n...@hotmail.co mwrote:

er wrote:

hi,

>

here's why i'm trying to do:

>

header1.hpp
namespace{ struct A{};}
struct B1{ A a; };

>

header2.hpp
namespace{ struct A{};}
struct B2{ A a; };

>

*.cpp
#include <libs/testing_namespa ce/header1.hpp>
#include <libs/testing_namespa ce/header2.hpp>

>

header2.hpp|5|e rror: redefinition of ‘struct<unnamed >::A’|

>

i should expect that because the translation unit includes both
header1 and header 2. so then how can i automatically generate unique
namespaces, one for each of header1 and header2?

>
You can't.  If you must, use a code generator.
>
If you automatically generate unique namespaces, how do you use them?
>
--
Ian Collins.

thanks.

yes... you also have to use the unique_namespac e::... throughout the
header, that's not practical.

[James Kanze]

Re: how to generate unique namespaces

On Sep 18, 5:04 am, Ian Collins <ian-n...@hotmail.co mwrote:

er wrote:

here's why i'm trying to do:

header1.hpp
namespace{ struct A{};}
struct B1{ A a; };

header2.hpp
namespace{ struct A{};}
struct B2{ A a; };

*.cpp
#include <libs/testing_namespa ce/header1.hpp>
#include <libs/testing_namespa ce/header2.hpp>

header2.hpp|5|e rror: redefinition of ?struct<unnamed >::A?|

i should expect that because the translation unit includes
both header1 and header 2. so then how can i automatically
generate unique namespaces, one for each of header1 and
header2?

You can't.

For some definition of "unique". Something like:

namespace header1_private { /* ... */ }

is sufficient for a lot of cases. Or for the really paranoid:
corporate_name_ division_name_d epartement_name _header1.

And since nobody has mentionned it: you almost never want an
anonymous namespace in a header. In his case, for example, if
header1.hpp is included in more than one translation unit, he
has undefined behavior, because of a violation of the one
definition rule for B1.

If you must, use a code generator.

Like you do for the include guards?

If you automatically generate unique namespaces, how do you
use them?

As you said, with a code generator:-). As long as everything is
generated by the same code generator, everything is hunky dory.
(This works for include guards because except for the #ifdef and
immediately following #define, you never use the symbol. And
those are automatically inserted by the "code generator" when
you create the file.)

--
James Kanze (GABI Software) email:james.kan ze@gmail.com
Conseils en informatique orientée objet/
Beratung in objektorientier ter Datenverarbeitu ng
9 place Sémard, 78210 St.-Cyr-l'École, France, +33 (0)1 30 23 00 34

[PeterAPIIT@gmail.com]

Re: how to generate unique namespaces

How to merge a namespace with another namespace with different header
like C++ did as namespace std consists of many header file?

Thanks.

[PeterAPIIT@gmail.com]

Re: how to generate unique namespaces

On Sep 18, 9:08 pm, Michael DOUBEZ <michael.dou... @free.frwrote:

PeterAP...@gmai l.com a écrit :
>

How to merge a namespace with another namespace with different header
like C++ did as namespace std consists of many header file?

>
Simply use the same namespace name:
>
a.h
-------
>
namespace myspace
{
struct A {};}
>
-----------------
>
b.h
-------
>
namespace myspace
{
struct B {};}
>
-----------------
>
myspace::A var_a;
myspace::B var_b;
>

A billion thanks for your help.

[er]

Re: how to generate unique namespaces

On Sep 18, 4:55 am, James Kanze <james.ka...@gm ail.comwrote:

On Sep 18, 5:04 am, Ian Collins <ian-n...@hotmail.co mwrote:
>
>
>

er wrote:

here's why i'm trying to do:
header1.hpp
namespace{ struct A{};}
struct B1{ A a; };
header2.hpp
namespace{ struct A{};}
struct B2{ A a; };
*.cpp
#include <libs/testing_namespa ce/header1.hpp>
#include <libs/testing_namespa ce/header2.hpp>
header2.hpp|5|e rror: redefinition of ?struct<unnamed >::A?|
i should expect that because the translation unit includes
both header1 and header 2. so then how can i automatically
generate unique namespaces, one for each of header1 and
header2?

You can't.

>
For some definition of "unique".  Something like:
>
    namespace header1_private { /* ... */ }
>

Yep, that is also what I have turned to. Thanks for this and the other
answers.

is sufficient for a lot of cases.  Or for the really paranoid:
corporate_name_ division_name_d epartement_name _header1.
>
And since nobody has mentionned it: you almost never want an
anonymous namespace in a header.  In his case, for example, if
header1.hpp is included in more than one translation unit, he
has undefined behavior, because of a violation of the one
definition rule for B1.
>

If you must, use a code generator.

>
Like you do for the include guards?
>

If you automatically generate unique namespaces, how do you
use them?

>
As you said, with a code generator:-).  As long as everything is
generated by the same code generator, everything is hunky dory.
(This works for include guards because except for the #ifdef and
immediately following #define, you never use the symbol.  And
those are automatically inserted by the "code generator" when
you create the file.)
>
--
James Kanze (GABI Software)             email:james.ka. ..@gmail.com
Conseils en informatique orientée objet/
                   Beratung in objektorientier ter Datenverarbeitu ng
9 place Sémard, 78210 St.-Cyr-l'École, France, +33 (0)1 30 23 00 34