Syntax in C 's printf function for an Excel cell formatting

[dvsmas]

I need to send a report as an email with an attachment in an excel sheet format. Using awk, I could reformat the report ,with a "\t" in the printf statements as this is recognised as the cell separator in an xls file.
Is there any way I can set the font attributes also in a similar way?
This means I must give some character in printf so that it is recognised as a BOLD or so-and-so color when the xls is opened.
Thanks for any help