title: expression: deque iterator not incrementable (special case - i can't figure it out)
body: <p>I have something like <code>deq.push_back(object)</code> which works fine in a source file but not in another one - if I try the same operation there I get the runtime error in the title. How can it be possible? <code>deq</code> is a global variable in the source file where the code works. Just as a test, I tried to swap the global declaration and the extern between the source files and I get the same result, the second source file triggers the runtime error. What am I missing here? Why I can't use push_back from there?</p>