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

[phlebas.livejournal.com]

I don't know about limited character sets - I always assumed it was due to a collection of conversations including the line "The pound symbol. You know, the thing above the three." or similar.

'Hashtags' does seem especially odd given they apparently originated with someone who called it a pound sign.