constexpr static std::array<const char *,5> failing to compile with MSVC2013 - c++

Question

I have this code:
#include <array>
#include <iostream>
class ExternalGeometryExtension
{
public:
enum Flag {
Defining = 0,
Frozen = 1,
Detached = 2,
Missing = 3,
Sync = 4,
NumFlags
};
constexpr static std::array<const char *,NumFlags> flag2str{{ "Defining", "Frozen", "Detached","Missing", "Sync" }};
};
int main()
{
std::cout << ExternalGeometryExtension::flag2str[ExternalGeometryExtension::Frozen] << std::endl;
return 0;
}
It compiles fine with:
clang version 5.0.0 and
gcc (Ubuntu 4.8.4-2ubuntu1~14.04.3) 4.8.4
It fails to compile with MSVC2013.
The compilation error is:
C:\projects\freecad\src\Mod/Sketcher/App/ExternalGeometryExtension.h(47): error C2144: syntax error : 'int' should be preceded by ';' [C:\projects\freecad\build\src\Mod\Sketcher\App\Sketcher.vcxproj]
C:\projects\freecad\src\Mod/Sketcher/App/ExternalGeometryExtension.h(47): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int [C:\projects\freecad\build\src\Mod\Sketcher\App\Sketcher.vcxproj]
C:\projects\freecad\src\Mod/Sketcher/App/ExternalGeometryExtension.h(47): error C2146: syntax error : missing ';' before identifier 'flag2str' [C:\projects\freecad\build\src\Mod\Sketcher\App\Sketcher.vcxproj]
C:\projects\freecad\src\Mod/Sketcher/App/ExternalGeometryExtension.h(47): error C2838: 'array<char const *,5>' : illegal qualified name in member declaration [C:\projects\freecad\build\src\Mod\Sketcher\App\Sketcher.vcxproj]
C:\projects\freecad\src\Mod/Sketcher/App/ExternalGeometryExtension.h(47): error C2143: syntax error : missing ';' before '{' [C:\projects\freecad\build\src\Mod\Sketcher\App\Sketcher.vcxproj]
C:\projects\freecad\src\Mod/Sketcher/App/ExternalGeometryExtension.h(47): error C2334: unexpected token(s) preceding '{'; skipping apparent function body [C:\projects\freecad\build\src\Mod\Sketcher\App\Sketcher.vcxproj]
C:\projects\freecad\src\Mod\Sketcher\App\ExternalGeometryExtension.cpp(36): error C2143: syntax error : missing ';' before 'std::array<const char *,0x05>' [C:\projects\freecad\build\src\Mod\Sketcher\App\Sketcher.vcxproj]
C:\projects\freecad\src\Mod\Sketcher\App\ExternalGeometryExtension.cpp(36): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int [C:\projects\freecad\build\src\Mod\Sketcher\App\Sketcher.vcxproj]
C:\projects\freecad\src\Mod\Sketcher\App\ExternalGeometryExtension.cpp(36): error C2039: 'flag2str' : is not a member of 'Sketcher::ExternalGeometryExtension' [C:\projects\freecad\build\src\Mod\Sketcher\App\Sketcher.vcxproj]
c:\projects\freecad\src\mod\sketcher\app\ExternalGeometryExtension.h(47): error C2144: syntax error : 'int' should be preceded by ';' [C:\projects\freecad\build\src\Mod\Sketcher\App\Sketcher.vcxproj]
c:\projects\freecad\src\mod\sketcher\app\ExternalGeometryExtension.h(47): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int [C:\projects\freecad\build\src\Mod\Sketcher\App\Sketcher.vcxproj]
c:\projects\freecad\src\mod\sketcher\app\ExternalGeometryExtension.h(47): error C2146: syntax error : missing ';' before identifier 'flag2str' [C:\projects\freecad\build\src\Mod\Sketcher\App\Sketcher.vcxproj]
c:\projects\freecad\src\mod\sketcher\app\ExternalGeometryExtension.h(47): error C2838: 'array<char const *,5>' : illegal qualified name in member declaration [C:\projects\freecad\build\src\Mod\Sketcher\App\Sketcher.vcxproj]
c:\projects\freecad\src\mod\sketcher\app\ExternalGeometryExtension.h(47): error C2143: syntax error : missing ';' before '{' [C:\projects\freecad\build\src\Mod\Sketcher\App\Sketcher.vcxproj]
c:\projects\freecad\src\mod\sketcher\app\ExternalGeometryExtension.h(47): error C2334: unexpected token(s) preceding '{'; skipping apparent function body [C:\projects\freecad\build\src\Mod\Sketcher\App\Sketcher.vcxproj]
C:\projects\freecad\src\Mod/Sketcher/App/ExternalGeometryExtension.h(47): error C2144: syntax error : 'int' should be preceded by ';' [C:\projects\freecad\build\src\Mod\Sketcher\App\Sketcher.vcxproj]
C:\projects\freecad\src\Mod/Sketcher/App/ExternalGeometryExtension.h(47): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int [C:\projects\freecad\build\src\Mod\Sketcher\App\Sketcher.vcxproj]
C:\projects\freecad\src\Mod/Sketcher/App/ExternalGeometryExtension.h(47): error C2146: syntax error : missing ';' before identifier 'flag2str' [C:\projects\freecad\build\src\Mod\Sketcher\App\Sketcher.vcxproj]
C:\projects\freecad\src\Mod/Sketcher/App/ExternalGeometryExtension.h(47): error C2838: 'array<char const *,5>' : illegal qualified name in member declaration [C:\projects\freecad\build\src\Mod\Sketcher\App\Sketcher.vcxproj]
C:\projects\freecad\src\Mod/Sketcher/App/ExternalGeometryExtension.h(47): error C2143: syntax error : missing ';' before '{' [C:\projects\freecad\build\src\Mod\Sketcher\App\Sketcher.vcxproj]
C:\projects\freecad\src\Mod/Sketcher/App/ExternalGeometryExtension.h(47): error C2334: unexpected token(s) preceding '{'; skipping apparent function body [C:\projects\freecad\build\src\Mod\Sketcher\App\Sketcher.vcxproj]
C:\projects\freecad\src\Mod\Sketcher\App\ExternalGeometryExtensionPyImp.cpp(67): error C2039: 'flag2str' : is not a member of 'Sketcher::ExternalGeometryExtension' [C:\projects\freecad\build\src\Mod\Sketcher\App\Sketcher.vcxproj]
Full compiler output here
My questions are:
What I am doing wrong? Why is it not compiling with MSVC2013?
Is there something I can do to make this code work with MSVC2013 without breaking it in the other compilers?
EDIT: I have changed the code so that it is a Minimal, Complete, and Verifiable example as requested by Toby Speight based on the good guess of Diodacus. I cannot produce the error output of that specific code, because I do not have a copy of MSVC2003. I work on an opensource, FreeCAD, which offers Windows support. I use Linux. In any case, the errors in the output correspond to the code I show. This is the output of the AppVeyor test before integration. The code passes the Linux CI fine. I am going to try to make the most of this question, hopping that it is useful for others.
EDIT 2: I have realised that the double bracket initialization has raised some eyebrows. From the example in cppreference:
double-braces required in C++11 prior to the CWG 1270 revision
(not needed in C++11 after the revision and in C++14 and beyond)
Without double braces gcc 4.8 fails.

Answer 1

As per this microsoft devblog, constexpr is one of the C++11 core language features that is not supported in VS 2013. And it is only partially supported in "Nov 2013 CTP."

Answer 2

Well, the code in question does compile with C++17 option:
#include <array>
#include <iostream>
class ExternalGeometryExtension
{
public:
enum Flag {
Defining = 0,
Frozen = 1,
Detached = 2,
Missing = 3,
Sync = 4,
NumFlags
};
constexpr static std::array<const char *,NumFlags> flag2str{{ "Defining", "Frozen", "Detached","Missing", "Sync" }};
};
int main()
{
std::cout << ExternalGeometryExtension::flag2str[ExternalGeometryExtension::Frozen] << std::endl;
return 0;
}
And there is no need to redeclare static variable outside the class.
#Abdullah Tahiri Please use C++11 constructs (as stated in question labels) or go C++17 for all features. But I am afraid MSVC might be problematic with the code. Is there any special reason you cannot use GCC or CLang on Windows ?