Pure C. Where is the source code for the standard C library?

Question

C++ / C#

In general, I have MinGW. I got into the header files, and there are only function declarations and preprocessor directives and nothing more.
As I understand it, all header files are stored in object form.
I would like to know. Is this nonsense only on Windows or on Linux too?
Is the STANDARD LIBRARY (which is almost part of the language) some kind of secret?

Answer 1

Неужели СТАНДАРТНАЯ БИБЛИОТЕКА (которая почти часть языка) это какой-то секрет?

Вовсе нет:
glibc: https://sourceware.org/git/?p=glibc.git;a=tree
musl: git.musl-libc.org/cgit/musl/tree
uclibc-ng: repo.or.cz/uclibc-ng.git/tree
newlib: https://sourceware.org/git/gitweb.cgi?p=newlib-cyg...
Просто обычному человеку эти исходники почти никогда не нужны.