BOOST_FOREACH: What is the error on using this of a STL container?

Question

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;
}

Answer 1

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.

Answer 2

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.

Answer 3

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

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

Answer 4

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.