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My question is simple, maybe the answer is not.

In C++ (using Intel C++ 13.1 compiler on Win7) are global static variables always instantiated before main() is executed? If no, does it depends on the compile options (like /Ox)?

If they are declared and defined in DLL, is it the same?

Here is a case:

I have something like:

// in DLL.h
class MyClass
{
public:
    MyClass();
};

static MyClass *sgMyClassPtr;

and

// in DLL.cpp
MyClass *sgMyClassPtr = new MyClass;

MyClass::MyClass()
{
    // Code to execute here
}

Note that I omited the export declaration but it is correctly exported.

From my main application code, it seems that MyClass::MyClass() has not always been executed when I run it. I really don't understand but it looks like if the DLL had not been loaded yet or the static had not been correctly instantiated. Note that there is no threading and every call is synchronous (at least in my code!)

If you have any idea or suggestion, it will be appreciated. Thank you!

UPDATE 1

Maybe it will be easier if I tell you what I want to get rather than what I did...

I want to have a variable that is automatically instantiated at DLL load time. This variable will be registered (ptr stored in a std::set, say) by a singleton in the application (the .exe). The application singleton doesn't know about the DLL but the DLL knows the application singleton. So, on DLL load, I want the var to instantiate right now then registers itself in the application singleton. That is why I declared the var static inside the DLL and instantiated it there. The registration is done in the cTor.

My initial question was: does the static instantiation occurs right on DLL load or it may be delayed? I ask this question because sometimes I observe strange behaviours and it looks like an asynchronous problem... ???

dom_beau
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    Did you mean `extern MyClass* sgMyClassPtr` instead of `static *MyClass sgMyClassPtr`? – David Nov 01 '13 at 13:17
  • No. I mean static MyClass*. The var is declared and instanciated in the DLL. – dom_beau Nov 01 '13 at 13:40
  • here is a post that explains how variables are intialized http://stackoverflow.com/questions/17783210/when-are-static-and-global-variables-initialized – Gabriel Jan 05 '14 at 22:35

1 Answers1

0

The static initialisation occurs when the DLL is loaded, but depending on linker options, the DLL can be demand-loaded. Note that if you include the class in both the DLL and the main program but you don't export it from the DLL, then you'll get two copies of the code, and potentially two copies of your (class) static variables. So you might be getting confused by one copy not being initialised when the other one actually already has.

But make sure that you understand the linker options around lazy loading the DLLs first.

cliffordheath
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