Question

How can I convert this kind of data 08:00:43.771 given as string into a number specifying the number of milliseconds since midnight corresponding to this time instance?

Answer 1

I generally use the Matlab datenum outputs for timestamping in Matlab. Datenums are the number of days since 0/0/0000, expressed as a double (double precision numbers are precise to about 14 usec for contemporary dates).

Using datenums.

 currentDateTime1 = datenum('08:00:43.771');           %Assumes today 
 currentDateTime2 = datenum('6/8/1975 08:00:43.771');  %Using an explicit date

 millisecondsSinceMidnight = mod(currentDateTime1 ,1) *24*60*60*1000;  %Mod 1 removes any day component
 millisecondsSinceMidnight = mod(currentDateTime2 ,1) *24*60*60*1000;  %Then this is just a unit conversion

For unusual string formats, use the extended form of datenum, which can accept a string format specifier.