thank you very much Roy. So I went through the GCC Manual for gcc version 7.3.0 (https://gcc.gnu.org/onlinedocs/7.3.0/). I was looking for datatypes implementation but I have not found information which I need. There are some possible options like in the chapter >> 3.18.34 PDP-11 Options:
Use 16-bit int. This is the default.
However this is not valid for ARM (Cortex-M4 = ARMv7-M architecture) which I use, I think.
I am very curious where are the data types implemented. Where it is defined that int is 16-bit (half-word) or that short int is the same size as signed char etc. Does anybody know?