Hi there, Please excuse the OTness of this post. Since I am writing a library to be included in Debian, I feel that I should not be slaughtered for bothering you and hoping for your time and knowledge. This was on d-u until people told me that it would be less OT here. Thus, a repost... I have a question about shared libraries and C. Even though I did search the web, I could not find a reliable answer. I am writing a shared library with the intention to make it reentrant and thread-safe, if these concepts even apply. My question is about global variables -- I know they are bad programming style, but when it comes to debugging or subsystem initialisation in C, they are sometimes really necessary. If I use a global variable in a shared library, is it shared among all instances using that library? Here, I would say no because a process' memory space is separate from another's. However, what happens when I have a threaded process us the library? I have come up with two ways to deal without global variables in C: The first is to expect the user to instantiate a struct, e.g. a struct global_settings and pass it along to each function of the API. This is cumbersome but would work, although I could not be assured that it's always the same instantiation -- the user could create two objects and pass them alternatingly, thereby messing with the integrity of the global settings and the library code. It is questionable whether I should guard against such a case, but I feel like it ;^>. The other approach seems cleaner: I declare "extern" variables in the interface and expect the user to instantiate them, while I use them freely in the code. The problem here is that the user would have to do so on a global level in his/her code, so we'd have the same problem again, albeit the responsibility would be shifted from the library to the user code. I am not sure this is preferable. I'd be interested to hear your opinions, and how you deal with these challenges. -- Please do not CC me when replying to lists; I read them! .''`. martin f. krafft <madduck@debian.org> : :' : proud Debian developer, admin, and user `. `'` `- Debian - when you have better things to do than fixing a system Invalid/expired PGP subkeys? Use subkeys.pgp.net as keyserver!
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