Re: [Boost-users] [multi_index] passing 'cons t TYPE' as 'this' argument discards qualifiers

From: JOAQUIN LOPEZ MU?Z (joaquin_at_[hidden])
Date: 2007-12-27 11:59:47

----- Mensaje original -----
De: damny_at_[hidden]
Fecha: Martes, Diciembre 25, 2007 5:17 pm
Asunto: [Boost-users] [multi_index] passing 'cons t TYPE' as 'this' 
argument discards qualifiers
Para: boost-users_at_[hidden]

> merry xmas everyone,

Merry Xmas :)

[...]
> class cClass {
>  private:
>    int att1;
>  public:
>    std::string  nme;  // name
>    int               idf;    // identifier
>    cClass();
>    cClass(std::string nme, int idf);
>    int get_attribute();
> };
> 
[...]
>  mMapByNme::iterator itrNme = locMsg.get<0>().find("name1");
>  mMapByIdf::iterator itrIdf = locMsg.get<1>().find(456);
>  printf( "att1 = %d\n", itrNme->get_attribute() );
[...]
> main.cpp: In function `int main()':
> main.cpp:33: error: passing 'const cClass' as 'this' argument of 
> 'int cClass::get_attribute()' discards qualifiers
> Process terminated with status 1 (0 minutes, 20 seconds)
> 
> any hints how to solve the problem?

The problem here is that elements of a multi_index_container
are immutable, and the iterators ony grant const access
to them. In this regard, the behavior is the same as that
of a regular std::set. To solve your particular problem you can
const-qualify the offending member function:

  int get_attribute() const;

> how to encapsulate this special multi_index into a class, that 
> fits the above description of the needed 'map'.

You should probably consider whether Boost.Bimap could
be a better approach, but I see you're already discussing
this issue with Matías.

> are there possibilities to avoid the 'std::string' for the 'name' 
> key? 

I'm not getting this question. Could you please elaborate?

> where are the more easier examples for C++-templates/boost
> newbies like me :o) ?

HTH,

Joaquín M López Muñoz
Telefónica, Investiación y Desarrollo