Why does MSVC++11 rejects constexpr qualification

Question

So, playing around with constexpr, MSVC (Visual Studio 2012) gave me an error while trying to qualify my function with the constexpr keyword using this simple program (includes omitted):

constexpr int factorial(int n)
{
    return n <= 1 ? 1 : (n * factorial(n-1));
}

int main(void)
{
    const int fact_three = factorial(3);
    std::cout << fact_three << std::endl;
    return 0;
}

constexpr was underlined red with the following message:

Error : this declaration has no storage class or type specifier

and trying to compile the program gave the following output:

1>main.cpp(5): error C2144: syntax error : 'int' should be preceded by ';'

1>main.cpp(5): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int

It really puzzles me as it is the very example that Cppreference uses to illustrate the use of constexpr. At first I used a simple function that returned a literal, i.e. constexpr int func(){return 5;}, but which yielded the same error. I interpreted the first message as "it should be a member function of a struct or class", but the example from Cppreference shows that it's not necessary apparently.

So, what am I obviously missing here ?

Answer 1

Quite simply - because Visual Studio doesn't support constexpr (prior to Visual Studio 2015).

Note that MSVC++11 is Visual Studio 2012; VC++10 is Visual Studio 2010.