This must be a homework problem becauseAzzi just answered it two hours ago and told the student to use the fieldnames() function. You should tag homework problems with the "homework" tag. I'll do it now for you.
If you're using GUIDE, then all the option for each control's property are presented in the Property INspector in drop down list for that control. For example, the units property will show 'Characters', 'Normalized', etc. in the drop down list.
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