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GOTOphobia considered harmful in C

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Re: GOTOphobia considered harmful in C

#81

Post by marcosdumay »

hgsgm wrote: post #78
marcosdumay wrote: post #62

Earlier quoted context omitted.

In C# it's customary just to wave away the worst kinds of problem that C and D developers try to handle, and let the runtime kill your program. (This is more an artifact of why people pick their languages than anything inherent on the languages themselves.) But rest assured, your C# code is full of global state hidden on its runtime and is subject to the same kinds of errors people are discussing here.

"hidden on its runtime" keeps it out of the rest of thr program.

The entire program still has the same failure modes. If you wanted to handle them, you would get the same problems.

Re: GOTOphobia considered harmful in C

#82

Post by hgs3 »

pornel wrote: post #11

Manual goto cleanup is such a busywork, adding nothing of value, only places for potential leaks and UAFs. I know for C it’s unthinkable to standardize such a luxury like defer or destructors, so we’re going to relive arguments from 1968 for as long as C is used.

> I know for C it’s unthinkable to standardize such a luxury like defer or destructors, so we’re going to relive arguments from 1968 for as long as C is used.

There was a proposal for defer in C23 but it didn't make the cut [1]. There is also the __cleanup__ attribute if you're using GCC.

[1] https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2895.htm

Re: GOTOphobia considered harmful in C

#83

Post by arp242 »

Swenrekcah wrote: post #15
jitl wrote: post #9

There have been a bunch of major security vulnerabilities due to mistakes involving GOTO in C, being used as suggested by the article. Here’s a memorable one: https://www.imperialviolet.org/2014/02/22/applebug.html

I’d say this was more due to the case not being properly enclosed in brackets. Many people seem to really dislike using the brackets but this is what that gets you.

Lack of code review and testing always seemed like the most pressing problems with that; both of which should have caught this error. Yes, it probably also should have had braces, but that seems like the lesser issue.

Re: GOTOphobia considered harmful in C

#84

Post by ivalm »

arp242 wrote: post #77
ufo wrote: post #50

I always encourage people to go read Dijkstra's GOTO paper, instead of just its title. It's a short and easy read, almost like a blog post. If you pay attention, you can see that the he was talking about spaghetti code vs structured code. It's better when the lexical structure of the source code maps to the execution structure. That is, if you know what is the current line being executed, you have a good idea of what…

The thing is that many people today have never encountered the sort of spaghetti code that Dijkstra was talking about in 1968. There's plenty of confusing and messy code around, but true spaghetti code that GOTOs all over the place and is nigh-impossible to follow has been extremely rare for a long time. I can't recall encountering it in the last 30 years. It easy to misunderstand what he was even talking about becau…

Do you know of a good example you could link?

Re: GOTOphobia considered harmful in C

#85

Post by svieira »

ivalm wrote: post #84
arp242 wrote: post #77

Earlier quoted context omitted.

The thing is that many people today have never encountered the sort of spaghetti code that Dijkstra was talking about in 1968. There's plenty of confusing and messy code around, but true spaghetti code that GOTOs all over the place and is nigh-impossible to follow has been extremely rare for a long time. I can't recall encountering it in the last 30 years. It easy to misunderstand what he was even talking about becau…

Do you know of a good example you could link?

The first part of Guy Steele's talk on Fortress: https://www.infoq.com/presentations/Thinking-Parallel-Progra...

Re: GOTOphobia considered harmful in C

#86

Post by pavlov »

arp242 wrote: post #77
ufo wrote: post #50

I always encourage people to go read Dijkstra's GOTO paper, instead of just its title. It's a short and easy read, almost like a blog post. If you pay attention, you can see that the he was talking about spaghetti code vs structured code. It's better when the lexical structure of the source code maps to the execution structure. That is, if you know what is the current line being executed, you have a good idea of what…

The thing is that many people today have never encountered the sort of spaghetti code that Dijkstra was talking about in 1968. There's plenty of confusing and messy code around, but true spaghetti code that GOTOs all over the place and is nigh-impossible to follow has been extremely rare for a long time. I can't recall encountering it in the last 30 years. It easy to misunderstand what he was even talking about becau…

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 by 1979 standards — it’s in a printed book after all.

There’s an auxiliary listing after the program itself explaining the routines and variables used, but many/most programs in those days wouldn’t have this level of rigorous documentation. Deciphering the program would probably have to start by drawing a flowchart of execution paths.

Re: GOTOphobia considered harmful in C

#87

Post by aliceryhl »

bitwize wrote: post #51
WalterBright wrote: post #29

The C version: int* foo(int bar) { int* return_value = NULL; if (!do_something(bar)) goto error_1; if (!init_stuff(bar)) goto error_2; if (!prepare_stuff(bar)) goto error_3; return_value = do_the_thing(bar); error_3: cleanup_3(); error_2: cleanup_2(); error_1: cleanup_1(); return return_value; } The D version: int* foo(int bar) { scope(exit) cleanup1(); if (!do_something(bar)) return null; scope(exit) cleanup2(); if…

It's still wrong by default. The correct pattern here is RAII, which requires no explicit cleanup code so there's no forgetting to use it.

The article specifically talks about C, which does not have RAII.

Re: GOTOphobia considered harmful in C

#88

Post by tester756 »

owisd wrote: post #26

> On the other hand, today we have the very opposite situation: programmers not using goto when it's appropriate and abusing other constructs, what ironically makes code only less readable. One I see all the time from beginners is creating a finite state machine using one method per state and jumping between states by calling the next state’s method from within the current state’s method. Essentially just emulating g…

Where in the world beginners use state machines instead of switch statement or if ladder?

this is genuine question, because I do believe that people do not use enough state machines to model their systems.

Re: GOTOphobia considered harmful in C

#89

Post by arp242 »

ivalm wrote: post #84
arp242 wrote: post #77

Earlier quoted context omitted.

The thing is that many people today have never encountered the sort of spaghetti code that Dijkstra was talking about in 1968. There's plenty of confusing and messy code around, but true spaghetti code that GOTOs all over the place and is nigh-impossible to follow has been extremely rare for a long time. I can't recall encountering it in the last 30 years. It easy to misunderstand what he was even talking about becau…

Do you know of a good example you could link?

Something like this is the best I could find: https://craftofcoding.files.wordpress.com/2018/01/fortran_go... – the last page has a full listing with arrows to show the jumps.

I grew up with MSX-BASIC: https://github.com/plattysoft/Modern-MSX-BASIC-Game-Dev/blob... – GOSUB jumps to a specific line number (RETURN returns from where it jumped). Even a fairly simple and clean example like this can be rather difficult to follow.

Re: GOTOphobia considered harmful in C

#90

Post by spacechild1 »

arp242 wrote: post #77
ufo wrote: post #50

I always encourage people to go read Dijkstra's GOTO paper, instead of just its title. It's a short and easy read, almost like a blog post. If you pay attention, you can see that the he was talking about spaghetti code vs structured code. It's better when the lexical structure of the source code maps to the execution structure. That is, if you know what is the current line being executed, you have a good idea of what…

The thing is that many people today have never encountered the sort of spaghetti code that Dijkstra was talking about in 1968. There's plenty of confusing and messy code around, but true spaghetti code that GOTOs all over the place and is nigh-impossible to follow has been extremely rare for a long time. I can't recall encountering it in the last 30 years. It easy to misunderstand what he was even talking about becau…

> but true spaghetti code that GOTOs all over the place and is nigh-impossible to follow has been extremely rare for a long time.

Exactly! Recently I had the "pleasure" to work with some FORTRAN IV code from the early 60s, so I know what you mean. No functions/subroutines, only GOTOs. Even loops were done with labels. There is also a weird feature called "arithmetic IF statements" (https://en.wikipedia.org/wiki/Arithmetic_IF). Luckily the code was pretty short (about 500 lines including comments).

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