platform-teensy-gcc10/examples/arduino-blink/include

This directory is intended for project header files.



A header file is a file containing C declarations and macro definitions

to be shared between several project source files. You request the use of a

header file in your project source file (C, C++, etc) located in `src` folder

by including it, with the C preprocessing directive `#include'.



```src/main.c



#include "header.h"



int main (void)

{

 ...

}

```



Including a header file produces the same results as copying the header file

into each source file that needs it. Such copying would be time-consuming

and error-prone. With a header file, the related declarations appear

in only one place. If they need to be changed, they can be changed in one

place, and programs that include the header file will automatically use the

new version when next recompiled. The header file eliminates the labor of

finding and changing all the copies as well as the risk that a failure to

find one copy will result in inconsistencies within a program.



In C, the usual convention is to give header files names that end with `.h'.

It is most portable to use only letters, digits, dashes, and underscores in

header file names, and at most one dot.



Read more about using header files in official GCC documentation:



* Include Syntax

* Include Operation

* Once-Only Headers

* Computed Includes



https://gcc.gnu.org/onlinedocs/cpp/Header-Files.html