How can vim display the number of characters selected in VISUAL mode?

  question, vim

This is my status bar setting:

set statusline=%{&ff}\|%{&fenc!  =''?  &fenc:&enc}\|%y\|c:%v\,r:%l\ of\ %L\|%f

The display effect is

unix|utf-8|PERL|c:1,r:1 of 63|256.pl

I want to add a display item to show the number of characters contained in VISUAL mode.

Write a function to calculate.

PS:g Ctrl-gYou can view the selected number of characters.