Override macro from the command line

Question

I would like to override a macro from the command line. Somewhere in my source, there is a definition like this:

#define MY_FOO 1

What I wo

Answer 1

If the file config.h prevents multiple inclusions (via #ifndef CONFIG_H etc), then you could abuse that:

g++ -DMY_FOO=2 -DCONFIG_H

Note: If the file config.h contains anything else that you need, then you have to define that yourself again as well. You could make a copy of the file as my_config.h and include that. (See also the -include file preprocessor option).