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GOTOphobia considered harmful in C

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Re: GOTOphobia considered harmful in C

#141

Post by billforsternz »

spacedcowboy wrote: post #61

I'm browsing this, and I'm not seeing the way I do it, which is sort-of-like #5 but not quite... I tend to wrap the code that has multiple exits-to-label in a do...while(0) loop, and use break to get there... So it might look like: do { if (false == call_func1()) { cleanup_any_state(); break; } if (false == call_func2()) { cleanup_any_state(); break; } } while (0); At any point you can branch to the common exit-state…

I don't like the code pattern if ( false == func() ). Function func() already returns a boolean, no need to compare that to a second boolean (false or true) to generate a third boolean.

Sorry, a little off topic I know.

Re: GOTOphobia considered harmful in C

#142

Post by saagarjha »

raldi wrote: post #132
preseinger wrote: post #120

Earlier quoted context omitted.

of course nobody should be writing C any more, for exactly the reason you're demonstrating in this comment

What language do you think Linux and Arduino should be programmed in?

If it was created today? I’d go for Rust and Python respectively

Re: GOTOphobia considered harmful in C

#144

Post by [deleted] »

BiteCode_dev wrote: post #52

I actually prefer "goto-less alternative 2". It's more verbose, but more explicit. No magic, I know exactly what happen. If you suddenly have more functions, you should have an array of functions with a clean_up_level variable. Of course, you probably should not have a global state that some clean up function with a side effect deals with in the first place, but it's the c linux kernel so I assume there is something…

[deleted]

Re: GOTOphobia considered harmful in C

#145

Post by codebje »

Someone wrote: post #103
pavlov wrote: post #86

Earlier quoted context omitted.

This. To find an example, I did a search for “Commodore PET Basic programs”. Here’s a book from 1979 that shows what spaghetti code looks like, in my opinion: http://www.1000bit.it/support/manuali/commodore/32_BASIC_Pro... The first program listing is on page 24 of the PDF. Try to follow the logic of the program. Why does line 400 go to 280? What paths can lead to line 400? Who knows! And this is high-quality BASIC b…

> And this is high-quality BASIC by 1979 standards — it’s in a printed book after all. I don’t think that’s true, certainly not for books of that time period. Because the whole field was changing rapidly, writers would often work under tight schedules, and customers would buy about anything because they only had magazines and books to learn from and review sites didn’t exist. I also think that’s bad Basic for the tim…

It looks pretty typical for BASIC of the late 70s to me.

You wouldn't want to waste characters on commenting code: machines of that era would have only a few KB of RAM, as low as 1K. For the same reason you don't want to waste characters on long, meaningful variable names or on well spaced code. Multiple statements per line isn't to save print space, it's to save RAM.

Meanwhile, the program's pretty well structured for such a short bit of BASIC: subroutines start at multiples of 100, for example, and each subroutine starts and ends clearly, no shenanigans like jumping from the middle of one sub to another, no multiple exit points for subs, all as linear as it can be. The use of IF is limited to skipping forward a short way to conditionally execute a line or two only. GOTO only exists in those IF statements.

I'd have been happy to have written code like this, back then.

I am pretty sure that my uncle ran this exact program on his computer and printed out biorhythms on listing paper, in the mid 80s.

Re: GOTOphobia considered harmful in C

#147

Post by eric__cartman »

saagarjha wrote: post #142
raldi wrote: post #132

Earlier quoted context omitted.

What language do you think Linux and Arduino should be programmed in?

If it was created today? I’d go for Rust and Python respectively

The ATmega 328P an Arduino Uno or Nano uses has 2KB of memory and 32KB of flash storage for the program. Having some sort of micropython interpreter there would be impossible, and even if it could be achieved, somone still has to write the low level C/ASM code to make it all work. For many embedded systems, low level languages like C or C++ (perhaps Rust for a lot of ARM micros) is the only sensible choice. If it's not a multi user system that's connected to a network, people trying to abuse memory unsafe code isn't a concern.

Re: GOTOphobia considered harmful in C

#148

Post by bee_rider »

spacechild1 wrote: post #138
bee_rider wrote: post #114

Earlier quoted context omitted.

Hmm, it is time to live Cunningham's Law I think: There’s no good way to do a do…while loop in Fortran, other than a goto.

Early Fortran already had loops, but with labels: INTEGER A(4,4), C, R ... DO 10 WHILE ( C .NE. R ) A(C,R) = A(C,R) + 1 C = C+1 10 CONTINUE Note that Fortran has evolved significantly over time. This is how you would write the same in Fortran 77: INTEGER A(4,4), C, R ... C = 4 R = 1 DO WHILE ( C .GT. R ) A(C,R) = 1 C = C - 1 END DO

Those are just regular loops, though, right? I’m looking for the posttest loop, sometimes known as the do…while or until loop. There seems to be a unfortunate inconsistency in the naming of this thing.

Re: GOTOphobia considered harmful in C

#149

Post by mort96 »

kmeisthax wrote: post #19

In RAII languages[0], you obviously don't need unrestricted gotos. However, I always find myself missing it when writing nested loops. Labeled break and continue[1] ought to be considered standard structure programming primitives. These are restricted gotos and allowing them to break or continue a parent loop doesn't unrestrict them much. But it does significantly improve the expressive power of your looping construc…

> [0] C++, Rust, Go, or anything else with automatic memory management and destructors

Go's automatic memory management (GC) doesn't come in to play here, but the defer statement does. It doesn't make Go a RAII language, but it makes Go a language with a nicer "run this code at the end of the stack frame" feature than goto.

Re: GOTOphobia considered harmful in C

#150

Post by photochemsyn »

I'd guess you could use function pointers to implement the example without goto?

https://www.opensourceforu.com/2012/02/function-pointers-and...

Then I looked up 'callbacks considered harmful'. Hmmm....

It's probably easier for an IDE to track down a function if you want to see how the code works, however, and the function might have some useful explanatory comments.

Suggested article: "People who claim code can explain itself considered harmful"

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