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Forum Index : Microcontroller and PC projects : Strange subroutine behaviour
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| BrianP Senior Member  Joined: 30/03/2017 Location: AustraliaPosts: 292 |
Hi all I'm having a very strange (to me) issue with a very simple subroutine in a current program development. If set as a subroutine (sub xxx / end sub) structure it will not work (doesn't get called - but no errors. An END or PAUSE statement as the first line is never executed). The calling method is by the name only DATESWAP as in the manual & all other subroutines in the program do work correctly using this method. I've tried renaming it without success. Again, all other subroutines in the program work fine this way. If I set it as a Label & call it with gosub DATESWAP it works! As will be obvious the purpose of this routine is solely to convert the DATE$ format to display as European format (yyyy-mm-dd). Try as I might I cannot get it to work as a subroutine - only as a label. No big deal, but curious as to why? I'm probably missing something very basic (no pun) but this is as per the example in the MMBasic v.5.4 manual. Current version is 5.405 on an E28 MK2. (But I am anal retentive...) Losing more of the already thinning hair... (age 74) Examples below... Cheers Brian P. 'if called as a label - gosub DATESWAP - it works as intended ' DATESWAP: edate$=right$(date$,4)+mid$(date$,3,3)+"-"+left$(date$,2) RETURN ' ' 'if called as a sub - DATESWAP - it never happens (or should I use GOTO DATESWAP?) ' SUB DATESWAP edate$=right$(date$,4)+mid$(date$,3,3)+"-"+left$(date$,2) END SUB ' |
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CaptainBoing Guru  Joined: 07/09/2016 Location: United KingdomPosts: 1994 |
Hello Brian I copied your code got the following: > list Dim edate$ Print edate$ 'just to show the variable is ok dateswap Print edate$ ' after the Sub 'if called as a label - gosub DATESWAP - it works as intended ' 'DATESWAP: 'edate$=Right$(Date$,4)+Mid$(Date$,3,3)+"-"+Left$(Date$,2) 'Return ' ' 'if called as a sub - DATESWAP - it never happens (or should I use GOTO DATESWAP?) ' Sub DATESWAP edate$=Right$(Date$,4)+Mid$(Date$,3,3)+"-"+Left$(Date$,2) End Sub ' > RUN 2000-01-01 > which I think is what you are after(?). Can you try the simple bit above like I did? if that works then the problem lies elsewhere As an aside, be careful here - if this code runs across midnight you could get weird edates - best to copy the date to a local variable in the SUB and use that h |
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| flip Senior Member Joined: 18/07/2016 Location: AustraliaPosts: 114 |
Good day Brian, I too have seen this behaviour in MM for DOS, and it turned out to be a structural problem with my program. As CaptainBoing has shown, the code works, so of itself, that code is not the problem. I use Jim's MMEDIT - it has some checking tools available, and using MM for DOS (if possible) as it saves write cycles. It was either DIM statements within the subroutine or badly nested loops and IF statements that a full tidy up using MMEDIT fixed. Hope this helps Regards Phil. |
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| BrianP Senior Member Joined: 30/03/2017 Location: AustraliaPosts: 292 |
@CaptainBoing - thanks for the input. The issue is not that the routine doesn't work as designed, but that when it is called from earlier in the program as a sub, eg. DATESWAP:event$(logcount)=edate$+" | "+time$ it doesn't work (if I put a PAUSE or END as the first line in the routine it is ever executed so either it not being called or it exits immediately when called). If structured as a Label (DATESWAP: / RETURN format) & called from the program it works, eg. gosub DATESWAP:event$(logcount)=edate$+" | "+time$ All the other subs in the program (SUB XXX / END SUB format) work as intended when called. So why doesn't this particular one? BTW this routine is only used to timestamp an event log entry so a random corruption at midnight wouldn't be an issue, particularly as the log creation is purely on demand & would only take <100msec (I would think). Point taken tho... I've worked around the issue by calling it as a label. but I want to know WHY?  Thanks for thinking about it B |
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| flip Senior Member Joined: 18/07/2016 Location: AustraliaPosts: 114 |
Brian, This code works as you want: Dim edate$ Print edate$ Gosub DateSwap Print edate$ End If x$="" Then DateSwap: edate$=DATE$ Return but this doesn't... Dim edate$ Print edate$ DateSwap Print edate$ End If x$="" Then Sub DateSwap edate$=DATE$ End Sub The reason one works and one doesn't is because of the extraneous If statement around the code. This is only one way it can stuff up...without seeing all the code hard to say but if you look around your sub for IF statements or loops that might 'hide' the routine from the interpreter EDIT !! this didn't exactly do it but I am sure I'm onto the track Regards, Phil |
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TassyJim Guru Joined: 07/08/2011 Location: AustraliaPosts: 5923 |
I would put it into a function Jim VK7JH MMedit MMBasic Help |
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| TassyJim Guru Joined: 07/08/2011 Location: AustraliaPosts: 5923 |
Without seeing more of your code I am not sure but try putting a space after DATESWAP and before the colon. DATESWAP:event$(logcount)=edate$+" | "+time$ Change to: DATESWAP :event$(logcount)=edate$+" | "+time$ The interpreter might be getting confused with DATESWAP: at the start of the line looking too much like a label. I still prefer a function. Jim VK7JH MMedit MMBasic Help |
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| WhiteWizzard Guru Joined: 05/04/2013 Location: United KingdomPosts: 2794 |
@BrianP Out of interest, is it still an issue if you split into two lines? DATESWAP event$(logcount)=edate$+" | "+time$ WW For everything Micromite visit micromite.org Direct Email: whitewizzard@micromite.o |
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| flip Senior Member Joined: 18/07/2016 Location: AustraliaPosts: 114 |
I was off track before, Jim is spot on (2 posts up)...if you put the space where he said or change the line DATESWAP:event$(logcount)=edate$+" | "+time$ to 2 lines:DATESWAP it works fine with Sub event$(logcount)=edate$+" | "+time$ For some reason it is confused by the statement separator (as it's thinking its a label) I've confirmed problem with MMBasic for DOS: Print edate$;"." DateSwap:Print "Hello." Print edate$;"." SUB DATESWAP edate$=right$(date$,4)+mid$(date$,3,3)+"-"+left$(date$,2) END SUB > RUN . Hello. . > Following works OK (after splitting conjoined statement to 2 lines) Print edate$;"." DateSwap Print "Hello." Print edate$;"." SUB DATESWAP edate$=right$(date$,4)+mid$(date$,3,3)+"-"+left$(date$,2) END SUB > RUN . Hello. 2017-08-18. > So it needs a space before the statement separator, but arguably it might be more readable putting each statement on a separate line. Regards, Phil |
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MicroBlocks Guru Joined: 12/05/2012 Location: ThailandPosts: 2209 |
One thing of minimizing problems is to minimize the use of labels!. :) Labels have a problem that code can 'fall through' them especially if you use them for subroutines. There is no way for the interpreter to match labels with return statements. Better use SUB/END SUB to prevent hard to find bugs. Microblocks. Build with logic. |
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Geoffg Guru Joined: 06/06/2011 Location: AustraliaPosts: 3167 |
This is the problem, DATESWAP is interpreted to be a label because it meets the rules of a label (ie, an identifier followed by a colon). This also means that the colon is not a separator but part of the label. A space before the colon is not valid in a label so that colon is treated as a separator. Geoff Geoff Graham - http://geoffg.net |
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| BrianP Senior Member Joined: 30/03/2017 Location: AustraliaPosts: 292 |
YES! Geoff / Flip / WW / Jim / CaptainBoing's ideas / suggestions are spot on. Although, this issue only seems to arise when the sub is called from within another sub - I haven't the problem with other subs called from the main program (without the space). This gives rise to another question though - what should we do as a preferred programming practice? Always use a space after a sub call? Or is this a bug, which might be sorted down the track? @MicroBlocks - yes, I agree about using labels, Should only be used as a program section header or a goto destination (if you must!). Jim - point taken on board re function - would a function call be noticeably faster than a sub call? Speed is not an issue in this case though. Thanks everyone for your time & brain power on this - I don't like something happening without knowing WHY. (I did say I was anal retentive). Brian P. |
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| TassyJim Guru Joined: 07/08/2011 Location: AustraliaPosts: 5923 |
The interpreter would have difficulty differentiating between DATESWAP: the label and DATESWAP: a sub called DATESWAP followed by a : whenever they are at the start of a line. It is not a bug. I rarely use multi statement lines. When I do, I am careful about the spaces before and after the : I usually put in plenty of white space (for readability rather than functionality). I rarely use labels or goto's, but there are places for both. I normally choose functions whenever there is a single item to be returned. They tend to be more portable. I doubt if there is much speed difference. There is no right way, just plenty of wrong ways. Jim VK7JH MMedit MMBasic Help |
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| BrianP Senior Member Joined: 30/03/2017 Location: AustraliaPosts: 292 |
I guess I just don't like "waste" space(s)  Is this an issue that should be mentioned in the manual (or have I not seen it)? B |
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| CaptainBoing Guru Joined: 07/09/2016 Location: United KingdomPosts: 1994 |
time to divide the discussion: (INCOMING!!!!) Some simple rules I have always followed that are based around speed of code + readability: * nothing starts in column one except labels and comments (never use trim leading space). * Indent your code with a bare minimum of white space required to nest nicely and uniformly (big topic - develop a style that you are happy with). * avoid using reserved words in variable/procedure names where possible. * avoid duplicate maths where you can i.e. don't do a formula 3 times, do it once and assign the value to a variable - perform time trials to determine the best method. * Don't make a function/sub for something simple you are going to do lots of times from a single place. * you can have it big and fast or small and slow - perform trials based on speed/trade-off to determine the best method for an algorithm i.e. do I calculate a SIN with a polynomial of from a look-up table? For MMBasic I have augmented these with * Use short Procedure/variable names where possible - Code runs faster - self-documenting names are great - for compiled languages but wading in treacle for interpreted. * never put a space between a reserved word and its opening parenthesis - don't write ATN (0.5) - it's ATN(0.5). loads more that other have - we should develop a manual but it would need trial by combat to make it to the final print |
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