<p>Let's say I have a source file with many preprocessor directives. Is it possible to see how it looks after the preprocessor is done with it?</p>

Most compilers have an option to just run the preprocessor.
e.g.
, gcc provides -E:
```
```
-E  Stop after the preprocessing stage; do not run the compiler proper.  
       The output is in the form of preprocessed source code, which is sent
       to the standard output.
```
```
So you can just run:
```
```
gcc -E foo.c
```
```
If you can't find such an option, you can also just find the C preprocessor on your machine.  It's usually called cpp and is probably already in your path.  Invoke it like this:
```
```
cpp foo.c
```
```
If there are headers you need to include from other directories , you can pass -I/path/to/include/dir to either of these, just as you would with a regular compile.
For Windows, I'll leave it to other posters to provide answers as I'm no expert there.