@Justme, oh, I know, but I want to implement it universally, for every AVR microcontroller, using the preprocessor, maybe io.h somehow can help me to do it? Maybe I will use a table with information about the pin, ADC support, ADC number, etc, but I need to get this information every compilation time, in depend on a microcontroller to compile a program to.

@jwh20, I'm using an inner crystal clock source by default in AVR microcontrollers. It's not suitable for real time clock?

@PeteW, yeah, it worked, code size reduced to 472 bytes, thanks. You can post the answer if you want

@PeteW, my .map file: pastebin.com/raw/XuczgFXQ. What compiler arguments are you talking about? How can I enable garbage collection?

@MarcusMüller, so, how can I see the size of the program that will end up on the microcontroller? avrdude writes as much as the avr-size outputs: avrdude: 548 bytes of flash written

@MarcusMüller, I just removed a few unused methods from the class and the output from avr-size decreased from 682 bytes to 548.

@MarcusMüller, I analyzed the ELF file compiled by avr-g++. I don't use virtual functions. Output of avr-size is Program: 682 bytes and Data: 0 bytes