boost foreach with protected inheritance of container

I'm getting a compile time error with the following code. The error pops up on the use of BOOST_FOREACH on line 23:

17 class MyVec: protected std::vector<int>
18 {
19     public:
20         void add(int i) {   this->push_back(i); }
21         void print()
22         {
23             BOOST_FOREACH(int i, *this)
24                 std::cout << i;
25             std::cout << std::endl;
26         }
27 };

However, if I change protected to public at line 17, it compiles & runs as expected. Moreover, I can iterate just fine by using the standard boiler-plate code with iterators.

Why is this happening?? Any help would be appreciated! :-)

EDIT: Does this mean I cannot use BOOST_FOREACH without publicly exposing begin() & end() ? EDTI2: Actually, the const_iterator & iterator types also need to be exposed.

---

When you inherit with protected specifier, the public members of the base class become protected in the derived class.

BOOST::FOR_EACH implementation likely tries to call begin() and end() , but can't.

Adding two using declarations in the definition of MyVec solves it for me (I'm using gcc):

using std::vector<int>::begin;
using std::vector<int>::end;

---

If it helps understanding the error, consider this:

class MyVec;

void my_foreach(const MyVec&);

class MyVec: protected std::vector<int> {
    void print() {
        my_foreach(*this);
    }
};

void my_foreach(const MyVec& v)
{
    v.begin(); // error std::vector<int> is not an accessible base
}

I'm not familiar with the exact implementation of this macro, but I believe that's the crux of the error you're getting. If you're interested, dive in the source code for it and maybe read this nice article for an explanation.

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