Finding chars in strings

[Jonathan M Davis via Digitalmars-d-learn]

On Tuesday, September 05, 2017 18:04:16 ag0aep6g via Digitalmars-d-learn 
wrote:
> On 09/05/2017 05:54 PM, Per Nordlöw wrote:
> > Follow up question: If a character literal has type char, can we always
> > assume it's an ASCII character?
>
> Strictly speaking, this is a character literal of type char: '\xC3'.
> It's clearly above 0x7F, and not an ASCII character. So, no.
>
> But if it's an actual character, not an escape sequence, then yes (I
> think). A wrong encoding setting in your text editor could mess with
> that, though.

Aside from escape sequences, a literal should not result in a non-ASCII
value for a char, but in general, it's a bad idea to assume that a char is
an ASCII character unless you've verified that already or somehow know based
on where the input came from that the char or chars that you're dealing with
are all ASCII. And you have to remember that VRP is in play as well, so if
it gets involved, you could end up with a char that's not an ASCII
character. And IIRC, character literals are almost always treated as dchar
unless a cast or VRP gets involved. So, I wouldn't be in a hurry to assume
that using character literals would guarantee that you're dealing with only
ASCII. Ultimately, std.ascii.isASCII is your friend if there's any risk of
something not being ASCII when you need it to be ASCII.

- Jonathan M Davis