Len() as argument for Dir() - excel

Question

So I am looping through a folder and have set a few arguments to filter the loop. I am trying to do so for file length as well but I am getting a run time error 13 type mismatch. Guessing there's no way to use file length as an argument for Dir()? What's a good workaround?
path = subF & "\"
extension = "*.xlsm"
partialName = "C*"
file = Dir(path & partialName & Len(file) = 13 & extension) '<- error
I can do
length = Len(file)
If length = 13 Then
inside the loop but without going into details, I need to do so outside of the loop.
Neither this or this is helping. And SO seems to only discuss file length with python not excel :/

Answer 1

You want filenames that are a total of 13 characters long to include a period and a four letter file extension, so you really want filenames that are 8 characters long and starts with a C. The file mask you are currently using involved the asterisk which is the wildcard character for any number of characters. Switch to seven (7) question marks after the C and you should be filtering your Dir function for file names that are eight characters long starting with a C with an .xlsm file extension.
path = subF & "\"
extension = ".xlsm"
partialName = "C???????"
file = Dir(path & partialName & extension) '\C???????.xlsm

Answer 2

Remove the * wildcards and use the '?' wildcard instead:
path = subF & "\"
partialName = "C"
extension = ".xlsm"
file = Dir(path & partialName & String(7, "?") & extension)
If you want 13 char between "C" and ".xlsm" use string(13, "?") instead.
Edit in response to comment:
Minimizing variables -
path = subF & "\C" & String(7, "?") & ".xlsm"
file = Dir(path)
or
file = Dir(subF & "\C???????.xlsm")