Question

I have this very simple piece of code;

#include <deque>
#include <vector>

using namespace std;

class A
{
public:
    A(){};
    ~A(){};
    deque<A> my_array; // vector<A> my_array;
};

int main(void)
{
}

If I compile this code with both g++ and icc/icpc on linux it compiles fine, even with -Wall it gives no warnings. If I swap the deque to a vector the situation is the same.

I would like to build this code on windows using MSVCC (cl) but unfortunately it throws error c2027:

error C2027: use of undefined type 'A'

If however I change the std::deque to a std::vector it compiles fine with Visual Studio 2010.

My question is; is this behaviour to be expected for some reason? If so, why are there differences between compilers or is this a mistake with either g++/icc or MSVCC?

Answer 1

It’s undefined behavior (both with std::deque and with std::vector,
so whatever an implementation does with it is fine, as far as the
standard is concerned. You’re instantiating a standard container with
an incomplete type.

When compiling with g++, -Wall (and in general, all options starting
with -W) only concern the language. For library issues, you should be
compiling with -D_GLIBCXX_CONCEPT_CHECKS -D_GLIBCXX_DEBUG
-D_GLIBCXX_DEBUG_PEDANTIC as well. (If this causes performance
problems, you can remove the last two -D in optimized builds.)