Constructor called twice on static std::map

Question

I am certain I have done something wrong to make this happen. I am using a library that declares a map statically in a way that seems to make sense.

In the header, in a class called Codec:

    typedef map< String, Codec* >::type CodecList; 
    static CodecList msMapCodecs;

In the cpp file:

    map< String, Codec * >::type Codec::msMapCodecs;

When I put a breakpoint on the line in the cpp file I have seen that it calls this in a stack frame called "__static_initialization_and_destruction_0" and if I step into it I can see it call the constructor for this map before main is reached. Just after main starts I insert some entries via function calls of the library API, then I notice the constructor is called a second time in a similar way to first.

What could cause this, or what and I misunderstanding that could confuse me enough to think this is happening? I have searched and I don't see an explicit calls to the constructor. I could not duplicate this in a minimal test case. I know that providing an exact answer is not possible, but anything that will point me a good direction would be appreciated.

If it matters I am using gcc 4.6.3 on Ubuntu 12.04. x64

One call in initialization and one call, when use? Are you sure, that second call is call to default constructor (not call to copy c-tor)? — ForEveR, Oct 04 '12 at 13:16
It is dynamically linked, and I copied the code verbatim. It must not be an std::map I will gets its actual type and post it. — Sqeaky, Oct 04 '12 at 13:17
As it's dynamically linked, you may want to check this question: http://stackoverflow.com/questions/2631918/main-program-and-shared-library-initializes-same-static-variable-in-static-ini . I have had the same issue - a constructor and destructor were called twice when linking dynamically (and just once, when static linking was used). I avoided this making the member non-static. But it was not the best solution (and it's not applicable for each situation) — Kiril Kirov, Oct 04 '12 at 13:18
@LyubomirVasilev - "In the header, **in a class called Codec**" — Kiril Kirov, Oct 04 '12 at 13:29
How is msMapCodecs ever populated? Neither the declaraion nor definition have an initialiser. — TheMathemagician, Oct 04 '12 at 13:46
@TheMathemagician When I Step through it it does indeed populate with a seemingly valid set of image codecs. I think Kiril probably has the answer with this. — Sqeaky, Oct 06 '12 at 19:30
@KirilKirov Thanks for the link that indirectly led me to the answer. — Sqeaky, Oct 06 '12 at 20:58
@interjay They have a struct that wraps std::map that presents a type member that is a typedef to the type of the internal map. I think it makes writing templates easier. — Sqeaky, Oct 06 '12 at 21:05

score 0 · Accepted Answer · answered Oct 06 '12 at 21:05

This was a visibility/symbol version issue problem. There are a variety of ways to have corrected this. Since this only exists with this compiler on this OS I decided to alter the header file slightly and maintain the changes myself. I will let creators of the library know in case they want to incorporate this change.

More details on symbol visibility can be found at: http://gcc.gnu.org/wiki/Visibility

Here are the changes I made to the code:

#if __GNUC__ >= 4
    // This block will be included only will the compiler
    #define DLL_LOCAL  __attribute__ ((visibility ("hidden")))
#else
    #define DLL_LOCAL
#endif

// <- Some details omitted here

typedef map< String, Codec* >::type CodecList; 
DLL_LOCAL static CodecList msMapCodecs;

Constructor called twice on static std::map

1 Answers1