lookup in a different spreadsheet
 

I have a spreadsheet that copied and is used by lots of people and it takes
alot of data from a code sheet, the code sheet itself changes regularly and
therefore sometimes we create newer versions and then update the master
spreadsheets references which is time consuming,.

I wanted to have the name and path of the code sheet set once and then use
that information within my lookups however I cant seem to work out how to do
the the following is an example I need to replace path\file with a cell
reference

=INDEX('path\[file]Sheet'!$C$4:$C$300,J$2+$A3,1)

can anyone advise, many thanks