How to use Regex to 'uppercase and replace' in Visual Studio Code's snippets?

Question

I want to create a snippet on Visual Studio Code 1.33.1 that create a C++ class using the file's name.
First, I want to set up the "include guard", the point is to use the file's name, replace every '.' by a '_' and set it all to uppercase (norm):
#ifndef FILE_CLASS_HPP //filename: File.class.hpp

The VSC documentation provides some variable for the file's name, and some Regex to change to all uppercase and replace a character by another.
Point is: I never managed to do both since I know nothing about Regex.

I tried to manually join the Regex but it never worked:
#ifndef ${TM_FILENAME/(.*)/${1:/upcase}/[\\.-]/_/g}

expected result:
#ifndef FILE_CLASS_HPP
actual result:
#ifndef ${TM_FILENAME/(.*)//upcase/[\.-]/_/g}

Answer 1

This should work:

"Filename upcase": {
  "prefix": "_uc",
  "body": [
    "#ifndef ${TM_FILENAME/([^\\.]*)(\\.)*/${1:/upcase}${2:+_}/g}"
  ],
  "description": "Filename uppercase and underscore"
},

---

([^\\.]*)(\\.)*  group1: all characters before a period
                 group2: the following period

replace with uppercase all the group1's: ${1:/upcase}

replace all the group2s ''s with _'s

The ${2:+_} is a conditional replacement, so you only add a _ at the end of group1 uppercase if there is a following group2.

The g global flag is necessary in this case to catch all the occurrences of group1group2's, not just the first.