Back to For Beginners

Static members

For Beginners

Started by belfegor March 23, 2012 12:57 PM

3 comments, last by SiCrane 12 years, 1 month ago

belfegor

2,836

Author

March 23, 2012 12:57 PM

Is this safe?



// Foo.hpp

struct Foo

{

    static int s1;

    static int s2;

    static int func()

    {

	    return s2 * 3;

    }

};



// Foo.cpp

int Foo::s1 = 6;

int Foo::s2 = s1 * 2;

...and then use it elswhere.
1. Is s1 guaranteed to be initialized first so i can init s2 safely?
2. Is s2 guaranteed to be initialized first so i can call func() safely?
3. Any possible problems?

SiCrane

11,840

March 23, 2012 01:14 PM

1) Yes
2) No. It's guaranteed to be initialized before either main() starts or it's first use if it's initialized after main() starts, but if you call foo() for static initialization in another translation unit you don't know if it'll be called before or after s2 is initialized. If you can guarantee all uses of foo() will only occur after main() starts you should be fine.

belfegor

2,836

Author

March 23, 2012 01:20 PM

So you mean its dangerous to use static members of one class in another class static functions, when they are in different translation units?

thanks for your time.

alvaro

21,604

March 23, 2012 01:25 PM

If you can guarantee all uses of foo() will only occur after main() starts you should be fine.

True, but in a large project, it's hard to maintain such guarantees, so I suggest you don't get in the habit of doing this type of thing. If you can avoid having global state, you should prefer that. If you can't avoid it, I like having an initialization function that needs to be called explicitly before you use anything in the class or library (like OpenGL requires you to call glInit(), for instance).

Some other opinions:

http://www.parashift.com/c++-faq-lite/ctors.html#faq-10.15
http://yosefk.com/c++fqa/fqa.html#fqa-10.15

SiCrane

11,840

March 23, 2012 01:35 PM

So you mean its dangerous to use static members of one class in another class static functions, when they are in different translation units?

Pretty much. C++ doesn't guarantee the order the runtime initialization order of different translation units. It can even change from one compile to the next.

Static members

This topic is closed to new replies.

Popular Topics

Recommended Tutorials

Static members

This topic is closed to new replies.

Popular Topics

Recommended Tutorials

Reticulating splines