Extract numbers from String on ATMega168
AVR libc has stdio functions in two flavors, one small (without floats) and another full-size with all features. See for example the description of vscanf from AVR libc,
basically you have to build with:

-Wl,-u,vfscanf -lscanf_flt -lm


And if you want to printf the variables you also have to add:

-Wl,-u,vfprintf -lprintf_flt -lm