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From: Thiago Adams <thiago.adams@gmail.com>
Newsgroups: comp.lang.c
Subject: Re: enums and switch vs function calls
Date: Sat, 5 Apr 2025 12:53:24 -0300
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Em 4/5/2025 7:29 AM, Richard Harnden escreveu:
> If I have:
> 
> enum colour {RED, GREEN, BLUE}
> 
> int colour_to_hex(enum colour colour)
> {
>      switch (colour)
>      {
>          RED: return 0xff0000;
>          GREEN: return 0x00ff00;
>          // BLUE: return 0x0000ff;
>      }
> 
>      ...
> }
> 
> ... then the compiler will warn me that I've missed a case in the switch 
> statement.  Which is good and very helpful.
> 
> But if I do:
> 
> int hex = colour_to_hex(10);
> 
> ... then the compiler doesn't complain that 10 is not in the enum.
> 
> Why? Surely the compiler can tell.

Sometimes enums are used as bit set.

f(BIT1 | BIT2)

this situation would generate a lot of warning because BIT1|BIT2 is not 
part of the enum, just BIT1 and BIT2 separately.

One way that this could be fixed is adding an attribute

[[bitset]]
enum E{ BIT1 = 2, BIT2 = 4};

Then the compiler would not generate a warning in this case.