std::vector of std::tuples leads to unknown size - c++11

Question

I want to store three arbitrary ints inside a std::vector without defining a struct/class. So I went for std::tuple<>:
std::vector<std::tuple<unsigned int, unsigned int, unsigned int>
Using MS VS 2013, it leads to the following error:
>c:\program files (x86)\microsoft visual studio 12.0\vc\include\vector(1628): error C2036: 'std::tuple<unsigned int,unsigned int,unsigned int> *' : unknown size
1> c:\program files (x86)\microsoft visual studio 12.0\vc\include\vector(1622) : while compiling class template member function 'void std::vector<std::tuple<unsigned int,unsigned int,unsigned int>,std::allocator<_Ty>>::_Tidy(void)'
1> with
1> [
1> _Ty=std::tuple<unsigned int,unsigned int,unsigned int>
1> ]
1> c:\program files (x86)\microsoft visual studio 12.0\vc\include\vector(945) : see reference to function template instantiation 'void std::vector<std::tuple<unsigned int,unsigned int,unsigned int>,std::allocator<_Ty>>::_Tidy(void)' being compiled
1> with
1> [
1> _Ty=std::tuple<unsigned int,unsigned int,unsigned int>
1> ]
1> d:\projects\gl33\src\nvf.cpp(39) : see reference to class template instantiation 'std::vector<std::tuple<unsigned int,unsigned int,unsigned int>,std::allocator<_Ty>>' being compiled
1> with
1> [
1> _Ty=std::tuple<unsigned int,unsigned int,unsigned int>
1> ]
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped =======
Is this due to limitations in the MSVS2013 compiler? Or am I doing something wrong?

Answer 1

A class type is known (its name is known) but its size is unknown if the type has only been forward-declared, but not defined. E.g.
struct X;
sizeof(X) // error: X is incomplete
The size of a type is important for pointer arithmetic, which is another hint when looking at the compiler error (which mentions a pointer to tuple).
MSDN provides the following example for C2036:
struct A* pA;
int main() {
pA++; // C2036, size of A not known
((char*&)pA)++; // OK, if sizeof(A) == sizeof(char)
}
Where the struct A* pa implicitly forward-declares struct A.
Such a situation can happen with headers of the Standard Library when you don't include all required headers yourself. There are interdependencies between the types in the Standard Library. If a Standard Library header requires only a forward-declaration of tuple, it won't include the heavyweight tuple header itself in an effort to reduce compilation times.
I could reproduce the issue in the OP by including only <vector> but not <tuple>. Solution: manually include all headers you need types from - when using vector<tuple<..>>, include <tuple> (as well as <vector>). In general, including a header guarantees the availability of a certain set of types. To maximize portability, always make sure the headers you've included guarantee that you can use all the types in your program(*).
(*) More specifically, you should make sure that you have a definition for all types your program needs a definition for. Standard Library containers require their value types to be complete (at least at the point where the class template is instantiated). Hence, if your program requires a definition of vector<tuple<unsigned, unsigned>>, it also requires a definition of tuple<unsigned, unsigned>.