[CMake] qt moc like feature

[Dietmar Hummel]

  Hi list!

Hopefulle you can help me with a problem I could not figure out how to do.
With a self written preprocessor, we add some generated code to our 
software.
This means the preprocessor is looking into the cpp files and is 
creating additional
code depending on some special marker found in the code. For most of the 
files of
the project there is just nothing to create.
Because this preprocessor tool is self written, we are free to either 
add this generated
code directly into the cpp file or to create a second module containing 
this code.

My problem is to find a cmake solution to start the preprocessor for all 
files of the project
but find a clean handling for the modified ones. In short words we are 
searching a solution
likely the same as Qt moc.

First idea was a solution based on following thread:
http://stackoverflow.com/questions/2354473/cmake-add-custom-command
but the problem seems to be that this solution must create an additional 
binary for every existing cpp file because the preprocessor is executed 
at compile time and I have no chance to only add these files to the 
project that are actually generated with useful content.

Second try was the idea to add the generated code directly into the cpp 
file itself and call the
preprocessor with something like that:

add_custom_command(
   OUTPUT ${binCmakeTestSources}
   COMMAND ${CMAKE_CURRENT_SOURCE_DIR}/dopoc2.bat "${binCmakeTestSources}"
   DEPENDS ${binCmakeTestSources}
)

This runs the preprocessor but the buildsystem always compiles all 
modules even if they are untouched....
Just two more questions: Is the Qt moc and uic handling in cmake some 
special implementation?
Could this be easily enhanced by me with adapting macros? For me it 
looks like this is some special Qt code inside cmake because i couldnt 
find any macros and it looks like the decision if moc(uic is to be run 
is made at cmake run not at c++ compile time...

Maybe somebody could give me a hint...

Regards
Dietmar