How do macros work in c?

Question

C++ / C#

Good time of the day.
I am using c without the standard library. But __DATE__ works for some reason. Explain how macros are implemented please and where to see their implementation.
ps code is executed at the hardware and bios levels. So it became interesting to me, it turns out that __DATE__ takes the date from bios? I can't figure it out myself in the compiler sources

Answer 1

www.opennet.ru/docs/RUS/cpp/cpp-5.html

'__DATE__'
This macro is replaced with a string constant that specifies the start date of the preprocessor. This constant is eleven characters long and looks something like '"Jan 29 1987"' or '"Apr 1 1905"'.

Answer 2

Google compilation steps. In particular - the preprocessor
https://en.wikipedia.org/wiki/C_preprocessor

Answer 3

__DATE__, __LINE__ and the like are substituted by the preprocessor itself. The implementation can be viewed only by downloading the source code of the compiler.