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]

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]

On Sep 17, 11:04*pm, Ian Collins <[e-mail] 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]

On Sep 18, 5:04 am, Ian Collins <[e-mail] 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:ja******* **@gmail.com
Conseils en informatique orientée objet/
Beratung in objektorientier ter Datenverarbeitu ng
9 place Sémard, 78210 St.-Cyr-l'École, France, [phone]

[PeterAPIIT]

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

Thanks.

[PeterAPIIT]

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]

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

On Sep 18, 5:04 am, Ian Collins <[e-mail] 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. [e-mail]
Conseils en informatique orientée objet/
* * * * * * * * * *Beratung in objektorientier ter Datenverarbeitu ng
9 place Sémard, 78210 St.-Cyr-l'École, France, [phone]