measuring the time used by the query

[Volnei Galbino]

Hello,    
    
 I am making a work in API C in the area of query optimization.     
 My problem this in measuring the time used by the query.
 I am using difftime(end,start) to evaluate the time, only he is
supplying it fear  in seconds, which, most of the time, it is not
relevant. 
How to do so that the time is supplied in second hundredths, for
example?    
Is there as doing this?    
    
Regards,
 
Volnei Galbino