The following snippet:

------------8<-------------

#include <memory>

typedef std::auto_ptr<int> v_type;

v_type fn(int v) {

    v_type r(new int(4));

    switch(v) {

        case 1:
        case 2: {

            return v_type(new int(5));

        } break;

        default:

            return r;
    }
}

int main(int argc, char *argv[])
{
    fn(4);
    return 0;
}

------------8<-------------

compiled with:

 g++ -Wall -Werror test.cpp

errornously produces:

error: control reaches end of non-void function

However, clearly, all control flow paths do return some result.
Without the "break" statement the code compiles flawlessly.