How are G, ħ & c measured??
Did you make any attempt to answer this on your own? As shown by the most trivial look up, you find that c is defined (not measured), and the measures of the others are described as below:
All of them may considered defined in some systems of units (for example, G is simply defined as 1 in some unit systems).
Wikipedia and Google are better starting points for basic question like this.
Separate names with a comma.