Why Fish not allowed to bind Ctrl + backslash?

[netherstar]

i tried to bind Ctrl + backslash but it doesn't work
bind \c\\ "do somethings"
also using fish_key_read with ctrl + backslash show nothing.

[faho]

If fish_key_reader shows nothing, that means the terminal sends nothing, and so fish can't tell that you've pressed it.

This is a limitation we can't do anything about. See https://fishshell.com/docs/current/cmds/bind.html#terminal-limitations

[netherstar]

but i can map Ctrl + \ in vim and it's work perfect.
I'm using Windows Terminal

[faho]

Okay, found it: It's typically bound in the terminal to sending the QUIT signal. It appears vim disables this, we can as well.

(one slight hiccup here is that \c\ is an awkward escape to give to a bind command, so I'm gonna make it so fish_key_reader gives it to you in hex form - \x1c).