I attempted to use the C++ Attach feature of Visual Studio Code using gdb on Linux Mint 17.3 and it did not work. I created a simple helloworld application. Launching the application for debugging (C++ Launch) worked fine but attaching to an existing process did not. I placed a cin statement in to ensure it was paused while I did the attach. Here's the console output:

=thread-group-added,id="i1"
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error while processing request 'evaluate' (exception: Specified argument was out of the range of valid values.\nParameter name: handle)