Use of Goto



  • I've just noticed this pattern (in 300 places) in some legacy code I've been inflicted with:

    [code] Goto(0, Line2); printf("some text"); [/code]

    This is plain old C for an 8051-type microcontroller.



  •  And? I would guess that the Goto function sets the cursor position on the screen. I don't see problem with that. Please explain.



  • @SenTree said:

    I've just noticed this pattern (in 300 places) in some legacy code I've been inflicted with:

    <font face="Lucida Console" size="2"> Goto(0, Line2); printf("some text"); </font>

    This is plain old C for an 8051-type microcontroller.

    Without seeing the definitions of Goto or Line2, it's pretty hard to know what's really going on here.




  • mol1111 is right, Goto sets the cursor position, Line2 is just a line number. My thought was that Goto (capitalised) was easily confused with goto (lower case). A different function name might have been helpful.

    No big deal, I just found it mildly amusing and wrote the post as a diversion from trying to untangle the rest of the spaghetti.



  •  I agree that the name can be confusing, especially for beginners.



  • @mol1111 said:

     I agree that the name can be confusing, especially for beginners.

    Beginners ? I would think that even more experienced people would prefer something like SetCursorPosition.



  • @SenTree said:

    My thought was that Goto (capitalised) was easily confused with goto (lower case). A different function name might have been helpful.

    Well, there ya go.  I would have thought that the fact that it's capitalised stands out like a sore thumb.  Even noobs learn pretty damn quick that C is case-sensitive and you can't go around capitialising the keywords.   And also, that's very visibly a function call rather than a statement, and it has these two arguments; I can imagine someone doing a brief double-take when they see it, but I don't see how they could go for any amount of time under the misapprehension that that was a goto statement.

    Still like you say it's a slow Monday morning round here ... :-)



  • @mol1111 said:

     I agree that the name can be confusing, especially for beginners.

    Beginners? Do beginners even know about goto, these days? I first learnt to program in BASIC so I was familiar with it, but I don't remember much mention being made of gotos when I learnt C, either in the book I learnt from or the classes I sat through a year or so later. I'm not sure I even knew they existed in C at first, and I certainly haven't used one since the BASIC days.



  • @DaveK said:

    I can imagine someone doing a brief double-take

    Did that, posted in haste, regretted at leisure.

    @DaveK said:

    Still like you say it's a slow Monday morning round here ... :-)

    Exactly... :D



  • @NSCoder said:

    @mol1111 said:

     I agree that the name can be confusing, especially for beginners.

    Beginners? Do beginners even know about goto, these days? I first learnt to program in BASIC so I was familiar with it, but I don't remember much mention being made of gotos when I learnt C, either in the book I learnt from or the classes I sat through a year or so later. I'm not sure I even knew they existed in C at first, and I certainly haven't used one since the BASIC days.

     

    goto is used in c (see e.g. zlib library). There are at least two good reasons to use goto:

    1) poor-mans exceptions:

    r = f();
    if (!r) goto fail;
    r = g();
    if (!r) goto fail;
    ...
    return OK;
    fail: /* handle errors */

    The idea is to separate normal code-flow and error handling.

    2) if you have specs of some state machine written in this way ("... 3] if something than go to to 2] else go to 5] ...") you may want to code itusing gotos to be as near as possible to the specs.



  •  @pitchingchris said:

    @mol1111 said:

     I agree that the name can be confusing, especially for beginners.

    Beginners ? I would think that even more experienced people would prefer something like SetCursorPosition.

    Yes, but they won't be confused just will think something bad about original coder.

     BTW I grew up on Borland and I'm completely happy with gotoxy :-)



  • @mol1111 said:

     @pitchingchris said:

    @mol1111 said:

     I agree that the name can be confusing, especially for beginners.

    Beginners ? I would think that even more experienced people would prefer something like SetCursorPosition.

    Yes, but they won't be confused just will think something bad about original coder.

     BTW I grew up on Borland and I'm completely happy with gotoxy :-)

    You and me both.


  • @mol1111 said:

     @pitchingchris said:

    @mol1111 said:

     I agree that the name can be confusing, especially for beginners.

    Beginners ? I would think that even more experienced people would prefer something like SetCursorPosition.

    Yes, but they won't be confused just will think something bad about original coder.

    Which was exactly what I did, and it's actually one of his milder WTFs. This guy perpetrated much of our original code, which we're still using 10-15 years later (industrial sensors change very slowly). I get a sinking feeling whenever I have to maintain some of his early stuff.

     BTW I grew up on Borland and I'm completely happy with gotoxy :-)

    Funnily enough, that's exactly the function name he used on later projects. I too am happy with that, and in fairness it does show that he improved over time.



  • @mol1111 said:

    goto is used in c (see e.g. zlib library). There are at least two good reasons to use goto:



    I recall seeing a goto in the original Half-Life's source code.  It fell mostly under the "poor-man's exceptions" category, I think, but I think it was used as an exit condition rather than an exception.  I'd have to see it again to be sure.



  •  It's also acceptable (IMO) to use goto as a "super-break" to break out of an inner and outer loop in one step. The alternative is to make a semiphore boolean and checking it each time through the outer loop.

     Javascript added the concept of labels, and the ability to continue to a specific label, to handle this case without using the "goto" keyword.



  • @blakeyrat said:

     It's also acceptable (IMO) to use goto as a "super-break" to break out of an inner and outer loop in one step. The alternative is to make a semaphore boolean and checking it each time through the outer loop.

     Javascript added the concept of labels, and the ability to continue to a specific label, to handle this case without using the "goto" keyword.

    Um, 'labels' are the term for what C uses to target gotos, and they're in a rather large portion of languages.  Perl also can break or continue to a label (well, technically, last, next, or redo - Larry recognized the semantic confusion presented by break and continue, fixed it in Perl, and then added in his own semantic confusion for good measure.)

    I suspect there are other languages which can perform similar loop flow operations.  I think I've actually used some, because I remember thinking Perl's redo was nifty, but the ability to break to a specific label didn't seem new.



  •  Sorry, I worded that funky. Labels obviously aren't the innovation; you're right, gobs of languages have those. The innovation is letting the "continue" keyword skip to a specific label optionally.

    Considering the text editor on this stupid forum breaks my browser's spell-checking, not being a spelling-Nazi would be nice.



  • @mol1111 said:

     BTW I grew up on Borland and I'm completely happy with gotoxy :-)

     

    I too grew up on Borland, but I used this instead:

    [code]push ds
    lds si,Source
    les di,Dest
    mov cx,Count
    mov al,TextAttribute
    mov ah,al ; Attribute goes in ah
    jcxz L2
    L1: lodsb
    stosw
    loop L1
    L2: pop ds[/code]

    Dest would be B800:0000 + (row*80 + col)*2 for color displays, B000:0000 + offset for monochrome.

    I could draw an entire screen worth of text on a 4.77 MHz 8088 without visible flicker, something TP could not do, much less the BIOS routines...

    (edit) How do you get whitespace in code snippets while avoiding visible "nbsp" tags??



  • @boh said:

    (edit) How do you get whitespace in code snippets while avoiding visible "nbsp" tags??
     

    With a browser that is (!Chrome && jsEnabled).

    <font face="Lucida Console" size="2">push ds
       lds si,Source
       les di,Dest
          mov cx,Count
          mov al,TextAttribute
       mov ah,al ; Attribute goes in ah
    jcxz L2
       L1: lodsb
    stosw
    loop L1
       L2: pop ds</font>



  • @boh said:

    (edit) How do you get whitespace in code snippets while avoiding visible "nbsp" tags??

    Use the raw editor. And they're entity references, not tags.

     



  • @Spectre said:

    Use the raw editor
     

    It is interesting to note that my advice is opposite to yours, but mine is accompanied by a working example.


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