How can I define macros for the C++ intellisense engine?

Project makefile defines are set in .vscode/c_cpp_properties.json.

"configurations": [
{
   ...
   "defines":[
       "MYSYMBOL",
       "MYVALUE=1"
   ]
}
], ...

Here are some methods to open c_cpp_properties.json:

1. Find a green squiggle on something like an include statement that Intellisense can’t resolve. Hover around and click the lightbulb that appears (which is tiny and a bit of a game to click). It will open the project config file in the editor.

2. Same as above, but put cursor on the green squiggle line and press Ctrl+..

3. Use the command pallet: ctrl+shift+P, then select C/C++: Edit configurations (JSON).

4. If the file already exists in your .vscode folder, open it with File->Open.

Although vscode will reprocess the settings after c_cpp_properties.json is modified, I found a restart is sometimes required when changing values.

There is basic and incomplete information here: https://code.visualstudio.com/docs/languages/cpp

This is a good link about the c_cpp_properties.json file itself: https://code.visualstudio.com/docs/cpp/c-cpp-properties-schema-reference