Juan Sanchez wrote:
So, what is the current build system and how does it work?


Everyone writes their own.  Most of the projects are for a single
developer.  Typically, they use GNU make.  I've been asked to
investigate a common build system.  Of course, everyone has their own
opinion about what a build system should be.

Sure, but they must have to set the compiler for the makefile at some point either by environment, PATH, or hard coding in the gnu makefile. Once run cmake will cache all the information needed
to build.  So, the environment is only needed the first time around.
Of the build systems I've investigated, CMake is the most attractive.
Except for the index, I think that the book you've written is excellent.

The only thing I'd really like clarification on is:

Would changing the compiler (64bit to 32bit) using environment variables
trigger massive recompilation (dependency hell) when changing the
setting back from (32bit to 64bit)?  Note that 32bit and 64bit would
have separate build directories.
If they are in separate build directories they would not affect each other at all. cd 32bit; make
cd 64bit; make.
Is the dependency checking that cmake uses as effective as "g++ -M"
(CPP)  in determining the dependencies?  Are the "#include" statements
in conditional macros tests honored when determining the dependencies?
Are the macro defines used in the compilation also passed along to the
dependency checker for each build variant?
No, they are not. CMake will potentially have extra depends that are not actually being used for the build. However, cmake's scanner is fast, and it is better to have extra depends than not enough. Having a full CPP could be done, but in practice it really has not caused problems
even for very large software systems.

-Bill

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