How to find editor position with line number and offset?

Hi 

I have a string to parse. When the parser parses it, we will get the output and that was the error, line number and offset.

I need to show an error popup on the editor with this insufficient details. 

So my question is how to plot ballon or Popup with just line number and offset(how many char in x position). 

Note: the output is new Editor so getting the caret model is not working.

Thanks in advance