CS+ for CC can't find uint sizes

i have a problem with the CS+ for CC IDE.
I wanted to run some sample code by initializing a variable like uint8_t test = 5.
Sadly, the IDE says that it can't find this datatype, even after the include of stddef.h.
My error message reads:
E0520020: Identifier "uint8_t" is undefined
I hope someone can explain to me where my error is.