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Understanding scope of variables - Printable Version +- Forum (https://www.boriel.com/forum) +-- Forum: Compilers and Computer Languages (https://www.boriel.com/forum/forumdisplay.php?fid=12) +--- Forum: ZX Basic Compiler (https://www.boriel.com/forum/forumdisplay.php?fid=11) +---- Forum: Help & Support (https://www.boriel.com/forum/forumdisplay.php?fid=16) +---- Thread: Understanding scope of variables (/showthread.php?tid=1038) |
Understanding scope of variables - georgeo - 03-11-2021 Hi everyone, In ZXBASIC, is this a valid program? Code: function myFunction( name$ as string ) as uinteger I have a variable labelled 'n' in both the top-level program and a function. I believe, in the function, 'n' is a different, locally defined variable, which is deleted when the function ends. Would the same work, if I replaced the function with a subroutine (accepting I couldn't return an answer in the same way)? I ask as I am seeing unexpected behaviour in my program (not the one above, a much longer program) and one possibility is that I'm using the same variable names for different entities in both the top-level program and subroutines. Thanks in advance for any help RE: Understanding scope of variables - georgeo - 03-11-2021 Actually, my question is more related to subroutines than functions. So, is the following code valid: Code: sub myFunction( byref total as uinteger, name$ as string ) Thanks again RE: Understanding scope of variables - RandomiserUsr - 03-12-2021 I believe scope in ZX BASIC is global and even if you include other .BAS files you have created, it seems that they all get collated then compiled as one. Not sure if this answers your question ? RE: Understanding scope of variables - boriel - 03-12-2021 (03-12-2021, 10:21 PM)RandomiserUsr Wrote: I believe scope in ZX BASIC is global and even if you include other .BAS files you have created, it seems that they all get collated then compiled as one. Yes, #include just puts the BASIC code at the place where the #include was placed. Another feature for libraries is still in progress. RE: Understanding scope of variables - boriel - 03-12-2021 (03-11-2021, 11:13 PM)georgeo Wrote: Actually, my question is more related to subroutines than functions. So, is the following code valid: Both SUB and FUNCTIONS are the same (with the small difference that FUNCTIONS are expected to return a value). When you DIM a variable within a function or sub, it's a *local* variable, and will be used only in that scope and destroyed upon exiting that scope. If there's another variable with the same name in an outer scope (i.e. the global one) this variable is "shadowed" by the LOCAL one and not accessible. So your program is OK (and use a Function, it's also OK. If you don't use DIM within a FUNCTION / SUB, the global variable will be used *if already declared*. If it's not declared, an implicit local variable is then created (which again is destroyed upon exiting). If you don't want this to happen, compile with --explicit, which will require every variable to be declared with DIM before use. This is very counterintuitive: Code: SUB test1() So to avoid test1() to implicitly declare a local var, compile with --explicit RE: Understanding scope of variables - georgeo - 03-13-2021 Hi Boriel, Thanks. That example makes things very clear. I think, in practice, using --explicit is a good idea to avoid most unexpected consequences. It is still important to watch out for previously defined values being picked up by subroutines, as in test2(). I guess putting function and subroutine definitions before the main program avoids that risk. Sadly, I'm seeing an issue using --explicit with the print42 library, as I'll explain in a new thread. Thanks again, |