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From: Muttley@DastardlyHQ.org
Newsgroups: comp.lang.c
Subject: Re: "A diagram of C23 basic types"
Date: Fri, 4 Apr 2025 09:40:58 -0000 (UTC)
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On Thu, 3 Apr 2025 15:58:05 +0200
David Brown <david.brown@hesbynett.no> wibbled:
>Human readers prefer clear code to comments.  Comments get out of sync - 
>code does not.

Thats not a reason for not using comments. Its very easy to understand your
own code that you've just written - not so much for someone else or for you
years down the line.

>Ignorance is curable - wilful ignorance is much more stubborn.  But I 
>will try.

Guffaw! You should do standup.

>Let me give you an example, paraphrased from the C23 standards:
>
>
>	#include <stddef.h>
>
>	enum Colours { red, green, blue };
>
>	unsigned int colour_to_hex(enum Colours c) {
>	    switch (c) {
>	        case red : return 0xff'00'00;
>	        case green : return 0x00'ff'00;
>	        case blue : return 0x00'00'ff;
>	    }
>	    unreachable();
>	}
>
>
>With "unreachable()", "gcc -std=c23 -O2 -Wall" gives :
>
>	colour_to_hex:
>         	mov     edi, edi
>	        mov     eax, DWORD PTR CSWTCH.1[0+rdi*4]
>	        ret
>
>Without it, it gives :
>
>	colour_to_hex:
>         	cmp     edi, 2
>	        ja      .L1
>	        mov     edi, edi
>         	mov     eax, DWORD PTR CSWTCH.1[0+rdi*4]
>	.L1:
>	        ret

Except its not unreachable is it? There's nothing in C to prevent you
calling that function with a value other than defined in the enum so what
happens if there's a bug and it hits unreachable? Oh thats right , its
"undefined" ie , a crash or hidden bug with bugger all info.

>Neither "// This should never be reached" nor "assert(false);" is a 
>suitable alternative.

In your opinion. I would never use that example above, its just asking for
trouble down the line.

Also FWIW, putting seperators in the hex values makes it less readable to me
not more.