4

Does anyone know why the following generates an error on VC9?

class Elem;
class ElemVec : public vector<Elem>
{
    public:
        void foo();
};

void ElemVec::foo()
{
    BOOST_FOREACH(Elem& elem, *this)
    {
        // Do something with elem
    }
    return;
}

The error I get is:

error C2355: 'this' : can only be referenced inside non-static member functions

The only (hack) solution I have right now which compiles without error is:

void ElemVec::foo()
{
    ElemVec* This = this;
    BOOST_FOREACH(Elem& elem, *This)
    {
        // Do something with elem
    }
    return;
}
Ashwin Nanjappa
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4 Answers4

4

You shouldn't inherit from STL containers. These are not polymorphic classes and it's the reason BOOST_FORACH can't handle your derived class.

Try to use aggregation instead.

Assaf Lavie
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1

Which compiler/Boost version are you using? I can compile the following without any problem (VS2005/Boost 1.38): 

#include <boost/foreach.hpp>
using namespace std;
struct xxx : std::vector<int>
{
    void test()
    {
        BOOST_FOREACH(int x, *this)
        {
        }
    }
}; 

int main(void) {
    xxx x;
    x.test();
    return 0;
}

Search the Boost bugbase if you want more details.

dirkgently
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0

I had never seen that error. I guess it comes from the implementation of BOOST_FOREACH macro.

May i ask why you're creating a class based on vector<...> and not having a vector member variable ?

EDIT Following this thread, i found out that this actually is a visual studio bug. The solution you have found seems to be the simplest.

Benoît
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  • In this case, I am extending the vector with some extra functionality that I need. – Ashwin Nanjappa Apr 04 '09 at 09:36
  • Generally a bad idea - write free functions instead of using inheritance. –  Apr 04 '09 at 09:41
  • Inheriting from vector is generally bad because of it's non virtual destructor. As long as you are aware of this, extending should be ok.. – Indy9000 Apr 04 '09 at 09:50
  • Benoit: I am aware of that Boost mailing list thread. What I'm surprised is that it hasn't been fixed since VC7/8 days! – Ashwin Nanjappa Apr 04 '09 at 09:52
  • @indeera unfortunately not only have you got to be aware of it, the users of your code have too –  Apr 04 '09 at 09:53
  • @Neil, I agree with you. Perhaps I didn't convey properly, I meant to say generally to cover wide range of scenarios, where as if the author knows the implications of his decisions, he could use this in a specific application. – Indy9000 Apr 04 '09 at 10:03
0

Hmm, all compiled succesfully on my msvc (2005) compiller.

Maybe you have some error, but fixed or avoided it when was created your example.

bayda
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  • Thanks, as "dirkgently" pointed out, it turned out to be a Boost issue. The error no longer occurs with the latest Boost v1.38. – Ashwin Nanjappa Apr 04 '09 at 11:03