Re: how to calculate the size of string in bytes?

[Eli Zaretskii <eliz@gnu.org>]

> Date: Tue, 18 Aug 2015 02:11:54 -0700 (PDT)
> From: Sam Halliday <sam.halliday@gmail.com>
> 
> Hi all,
> 
> We've had to change the ENSIME protocol to be more friendly to other editors and this has meant changing how we frame TCP messages.
> 
> We used to have a 6 character hex number at the start of each message that counted the number of multibyte characters, but we'd like to change it to be the number of bytes in the message.
> 
> We're sending the string to `process-send-string' and `read'ing from the associated network buffer. But when calculating the outgoing length of the string that we want to send, we use `length' --- but we need this to be `length-in-bytes' not the number of multibyte chars. Is there a built in function to do this or am I going to have to iterate the string and count the byte size of each character?

Emacs 25 has bufferpos-to-filepos, which I think does what you want.

> A quick test shows that
> 
>   (length (encode-coding-string "EURO" 'raw-text))
> 
> seems to give the correct result (1 for ASCII, 2 for Pound Sterling, 3 for Euro), but I am not 100% sure if this is correct.

It will fail if the string includes some exotic characters or raw
bytes.