You smell like ash, mildew and hash, can barely even speak

[venta]

Last night, ChrisC idly asked me why, on Twitter, hashtags are called hashtags.

Simple, I said, because they start with a #.

But, he said, they're called hashtags in the US, where the # is known as a pound sign.

I have a vague idea that # is sometimes called a pound sign; it's always struck me as a bit odd. I've always assumed it was related to the days when character sets were limited and it was used in place of £.

But of course they're hashtags. After all, they may call it a pound sign, but they don't pronounce it "pound".

But, said ChrisC, they do. In particular, in the US, C programmers talk about "pound defines".

This is just a bit of stray C syntax. Suppose you want your programme to limit the number of available heffalumps to 7, you can keep checking that:

heffalumps < 7

If you're worried that in the future you might want to allow more heffalumps you could do something like this:

#define MAX_HEFFALUMPS 7

and every time you want to check, you can just say:

heffalumps < MAX_HEFFALUMPS

Every time you write MAX_HEFFALUMPS a magical but dumb thing called the preprocessor will slavishly ensure that that gets treated as a 7. As computers improve and can fit more heffalumps in, you can just update it to:

#define MAX_HEFFALUMPS 24

instead of having to change it in lots of different places. This is commonly referred to as a "hash define". Lots of other instructions begin with the # character. See here for more detail than you can possibly want.

I'm sure at least someone will take serious issue with my AA Milne-based description of what the preprocessor does.

Pound defines?

Yes, he says. And pound includes. And pound ifs. And so on.

This is madness. Why wasn't I told? And can they be made to stop it?

And does anyone know why our American friends don't talk of poundtags?

Comments

[ewx.livejournal.com]

C99 includes the following example:

...which suggests that at least the term isn't totally alien to its (substantially American) audience, although of course it's possible that the author of that particular bit was European. I could find no other instance of 'hash' in the entire document - usually they just write "#" (perhaps a compromise l-)

[venta.livejournal.com]

I don't think C99 should be encouraing people to do that sort of thing :)

Interesting also that even while calling it hash_hash, the same (I presume!) writer refers to them as "sharp signs".

[ewx.livejournal.com]

Ooh, I'd missed the bit about sharp signs.

[undyingking.livejournal.com]

Caling them sharp signs is trebly confusing/dim, as the sharp sign is quite different.

[ewx.livejournal.com]

"Slightly different" would seem more accurate l-)

[undyingking.livejournal.com]

Maybe so, I get quite excitable about typography :-)