this post was submitted on 15 May 2025
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Tell me the truth ... (piefed.jeena.net)
submitted 1 month ago by [email protected] to c/[email protected]
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[–] [email protected] 0 points 1 month ago (1 children)

And compiler. And hardware architecture. And optimization flags.

As usual, it's some developer that knows little enough to think the walls they see around enclose the entire world.

[–] [email protected] 0 points 1 month ago (1 children)

I don't think so. Apart from dynamically typed languages which need to store the type with the value, it's always 1 byte, and that doesn't depend on architecture (excluding ancient or exotic architectures) or optimisation flags.

Which language/architecture/flags would not store a bool in 1 byte?

[–] [email protected] 0 points 1 month ago (1 children)

things that store it as word size for alignment purposes (most common afaik), things that pack multiple books into one byte (normally only things like bool sequences/structs), etc

[–] [email protected] 0 points 1 month ago (1 children)

things that store it as word size for alignment purposes

Nope. bools only need to be naturally aligned, so 1 byte.

If you do

struct SomeBools {
  bool a;
  bool b;
  bool c;
  bool d;
};

its 4 bytes.

[–] [email protected] 0 points 1 month ago (1 children)

sure, but if you have a single bool in a stack frame it's probably going to be more than a byte. on the heap definitely more than a byte

[–] [email protected] 0 points 1 month ago (1 children)

but if you have a single bool in a stack frame it’s probably going to be more than a byte.

Nope. - if you can't read RISC-V assembly, look at these lines

        sb      a5,-17(s0)
...
        sb      a5,-18(s0)
...
        sb      a5,-19(s0)
...

That is it storing the bools in single bytes. Also I only used RISC-V because I'm way more familiar with it than x86, but it will do the same thing.

on the heap definitely more than a byte

Nope, you can happily malloc(1) and store a bool in it, or malloc(4) and store 4 bools in it. A bool is 1 byte. Consider this a TIL moment.

[–] [email protected] 0 points 1 month ago

c++ guarantees that calls to malloc are aligned https://en.cppreference.com/w/cpp/memory/c/malloc .

you can call malloc(1) ofc, but calling malloc_usable_size(malloc(1)) is giving me 24, so it at least allocated 24 bytes for my 1, plus any tracking overhead

yeah, as I said, in a stack frame. not surprised a compiler packed them into single bytes in the same frame (but I wouldn't be that surprised the other way either), but the system v abi guarantees at least 4 byte alignment of a stack frame on entering a fn, so if you stored a single bool it'll get 3+ extra bytes added on the next fn call.

computers align things. you normally don't have to think about it. Consider this a TIL moment.