levy@mtcchi.uucp (2656-Daniel R. Levy(0000000)0000) (07/14/90)
Hi, I have a situation where I would like several routines in a library to set a global variable, which may or may not be declared in the program which uses the library. I also would like to be able to optionally compile a program that does reference the global variable with a different version of the library which does not reference the global variable. Most C compiler/linker systems I have used (on UNIX systems) honor the practice of declaring (uninitialized) globals in more than one file, though the strictly correct usage is to declare the global in only one file and declare externs in the rest. My trouble is that I can't take the strictly correct approach with my requirements above, declaring the global in only one place. Since I can't know whether a program calling a routine in the library is going to declare the global variable, I cannot just declare the variable as extern in the library routines or there may be link errors. Also, since I can't know whether a program using the global will be linked with my special library (without some pain) I cannot just declare the variable as extern in the program without similarly risking link errors. This has caused me some real hassle on a Sun4 running SunOS 4.0.3 (I don't know how to ask the compiler what version it is and "what" isn't very helpful). The use of the non-strictly-correct approach (declaring the global in all files) SOMETIMES results in the setting of a global in the library routine not being visible (!) in the program calling it. Yes, this is without any optimization in compiling both the library and the program. The addresses of the supposedly identical globals are wildly different when this happens. Changing the declaration in the program to extern "fixes" the problem but as I mentioned above this is not acceptable as a long term solution because I'd like to compile that same program with a library that doesn't declare the global. Now I could complain to Sun, but first I want to know, is there some evidence that this usage of multiple declarations of externs is "supported"? TIA -- Daniel R. Levy * Memorex Telex * Naperville IL * ..!uunet!tellab5!mtcchi!levy So far as I can remember, there is not one ... therefore be ye as shrewd word in the Gospels in praise of intelligence. as serpents and harmless as -- Bertrand Russell [Berkeley UNIX fortune] doves -- God [Matthew 10:16]
johnb@srchtec.UUCP (John Baldwin) (07/18/90)
In article <1990Jul14.002958.3546@mtcchi.uucp> levy@mtcchi.UUCP (Daniel R. Levy) writes: >............ I also would like to be able to optionally compile a program >that does reference the global variable with a different version of the >library which does not reference the global variable. Hunh? Maybe I need to understand this a little better first: what are you trying to do here? Is it that you have a program which already defines the global variable and you want it to work with two libraries, one which both defines and references a global of the same name, and another lib which neither defines nor references the global?