How to get the index of the font in excel?

[Chenghao Situ]

Hi,
   
  If a cell's value is "test string", and now only the "ing" is Strikeout.
  How can I get the exact index of this font's startIndex and endIndex?
   
  And if "tes" and "ing" are Strikeout, how can get the indexs for "tes" and 
"ing" seperatly?
   
  Thanks.

       
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