CODEWITHSUNDEEP
c++c++11
Abdullah Tahiri
Abdullah Tahiri

Reputation: 345

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

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.

Upvotes: 3

Views: 228

Answers (2)

Diodacus
Diodacus

Reputation: 673

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 ?

Upvotes: -1

P.W
P.W

Reputation: 26800

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."

Upvotes: 8

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