===================================
C By Example Part 2: C Preprocessor					[TOC]
===================================

In short: Using the option `-E` the `gcc` tool chain stops after running the C
preprocessor (CPP).  The result of CPP gets written to stdout (i.e. it gets
written to the terminal). Use this to see what input the compiler actually
gets.


---- VIDEO ------------------------------
https://www.youtube.com/embed/x9f-uqcm52E
-----------------------------------------

Supplement: More About Preprocessor Directives
==============================================
If you want to learn more about the preprocessor the internet is your friend.
There are many web sites with great content, here are two of them:

- __C Preprocessor (on gcc.gnu.org)__ is very comprehensive and perfect
  to look up each and every detail.
- __C Preprocessor (on Wikipedia)__ gives a nice overview and summarizes all the
  other directives not mentioned in the video.

Supplement: Compiler Options for Macro Definitions
=================================================

Consider

---- CODE (file=session04/foo.c) ---------------------------
hello world!
------------------------------------------------------------

With the option `-D` (__man gcc__) one can define macros. For example 

---- SHELL (path=session04) --------------------------------
gcc -Dhello=Hallo -Dworld=Welt -E foo.c
------------------------------------------------------------

CPP uses this options as if the first two lines of input file would be

---- CODE (type=c) -----------------------------------------
#define hello Hallo
#define world Welt
------------------------------------------------------------

You also can use the `-D` option to define an empty macro. Consider this source
file with a conditional directive:

---- CODE (file=session04/bar.c) ---------------------------
#ifdef de
Hallo Welt!
#else
hello world!
#endif
------------------------------------------------------------

with `-Dde` the macro is defined for the preprocessor processes the first line
of the source file:

---- SHELL (path=session04) --------------------------------
gcc -E bar.c
gcc -Dde -E bar.c
------------------------------------------------------------

Food for Thoughts
=================
How could you use the `-D` option so that the token `dummy` gets expanded to the
two tokens `foo bar`?


Quiz 04
=======

Consider the following C program:

---- CODE (file=session04/obscure.c) -----------------------
What
the(bloody  hell);

is
this()
{
    thing(doing);
}
------------------------------------------------------------

Add some directives but otherwise do not change the content so that it can
be compiled with

---- CODE -----------------------
gcc obscure.c
---------------------------------

into an executable that prints

---- CODE -----------------------
hello, world!
---------------------------------

Submit your solution with `submit hpc quiz04 obscure.c`

*Note:* There are no automatic tests and hence you will get no confirmation
email. However, if there is *no error message* then the submission was
successful. And if there was an error message then not successful. ;-)

:links: man gcc -> https://man7.org/linux/man-pages/man1/gcc.1.html
	C Preprocessor \(on gcc.gnu.org\) -> https://gcc.gnu.org/onlinedocs/cpp/
	C Preprocessor \(on Wikipedia\) -> https://en.wikipedia.org/wiki/C_preprocessor