How to minimize compilation time in C++

Question

I've coded an script that generates a header file with constants like version, svn tag, build number. Then, I have a class that creates a string with this information.

My problem is the following: As the file is created in every compilation, the compiler detects that the header has changed, and forces the recompilation of a large number of files. I guess that the problem is in the situation of the header file. My project is a library and header has to be in the "interface to the world" header file (it must to be public).

I need some advice to minimize this compilation time or to reduce the files forced to recompile.

Answer 1

In the header write something like:

extern const char *VERSION;
extern const char *TAG;
extern const char *BUILD_DATE;

and create a .c (or .cpp) file that will contain

const char *VERSION = "0.13";
const char *TAG = "v_0_13";
const char *BUILD_DATE = "2011-02-02 11:19 UTC+0100";

If your script updates the .c file, only that file will have to be recompiled, but the files that include your header won't.

Answer 2

Generate the constants in the implementation file.

Make sure the header doesn't get changed by your script.

Answer 3

The easiest way to solve this is to not make those constants in a header file. Instead, make functions in the header file which get these values. Then place the values themselves in a small cpp file which implements those functions. (Or place them in a header ONLY included in that cpp file). When you recompile, only that one file will need to be recompiled.

Also, you could look in to distcc to speed up compilation if you have a few machines to spare.