Static Member Data

random0 · 07-30-2006, 09:34 AM

I'm writing a shared library in C++ in which one of my classes contains a declaration of a static object of another class.

Code:

class class1
{
};

class class2
{
    private:
        static class1 object1;
};

class1 class2::object1;

g++ compiles this and the test program without problem and it links as well, but when I run my test program it seg faults on initialization. Any idea on what's going on?

vharishankar · 07-30-2006, 10:00 AM

I have an idea you cannot create static objects of classes. It's because of something to do with constructors/destructors and the like and the way they're called. Somebody correct me if I'm wrong...

P.S. That code doesn't even link because it returns an undefined reference to that object. You're trying to access something which doesn't even exist in memory.

Can you try and give the portion where you're actually using this? I am unable to recreate the scenario since I cannot even get the code to compile.

Bruce Hill · 07-30-2006, 10:38 AM

Also put your code in code tags, so we don't
see smiley faces, etc.

Nylex · 07-30-2006, 10:46 AM

Another minor thing is the missing semi-colons after the class' closing brace, e.g.

Code:

class class1
{
  // Stuff
};

random0 · 07-30-2006, 11:10 AM

Sorry about that lack of code tags. I ended up finding the error after a little gdb work and it was actually an unrelated bit of code that caused the error with class2. It's working properly now.

paulsm4 · 07-30-2006, 11:33 AM

Cool - glad you got it working.

And yes, of course you can create a static class object, if you need to! Or (as you did) a class that contains a static class object as a member.

vharishankar · 07-30-2006, 11:37 AM

Will it not lead to unpredictable program behaviour if static class objects are nested within other classes?

paulsm4 · 07-30-2006, 04:40 PM

Harishankar -

If you try hard enough, you can probably find a way to abuse just about any feature of any language. Heck - you probably wouldn't have too much difficulty finding at least a half dozen (or more!) ways to "mess up" adding two integer numbers in C++!

Nevertheless you can definitely have static class objects, whenever they're appropriate to your design.

And from what random0 posted, both his declaration and definition of "object1" seem perfectly OK.

IMHO .. PSM

PS:
Note the need for a default (no-argument) constructor to handle any initialization for static class objects.

spooon · 07-30-2006, 05:09 PM

Quote:

Originally Posted by paulsm4

PS:
Note the need for a default (no-argument) constructor to handle any initialization for static class objects.

Well, you just need a constructor to handle whatever initializer you used in your definition. Since here they gave no arguments in the initializer, they need a default constructor.