cmake add_custom_command

Question

I'm struggling with add_custom_command. Let me explain the problem in detail.

I've these set of cxx files and hxx files. I run a perl script on each of them to generate a certain kind of translation file. The command looks like

perl trans.pl source.cxx -o source_cxx_tro

and similarly for header.hxx files as well.

So I'll end up with some multiple commands (each for a file)

Then I run another perl scripn on the output generated from these commands (source_cxx_tro, header_hxx_tro)

perl combine.pl source_cxx_tro header_hxx_tro -o dir.trx

dir.trx is the output file.

I've something like this.

Loop_Over_All_Files()
Add_Custom_Command (OUTPUT ${trofile} COMMAND perl trans.pl ${file} -o ${file_tro})
List (APPEND trofiles ${file_tro})
End_Loop()

Add_Custom_Command (TARGET LibraryTarget POST_BUILD COMMAND perl combine.pl ${trofiles} -o LibraryTarget.trx)

What I expect is when building the post build target, the trofiles will be built first. but it is not the case. The ${trofiles} are not getting built and hence the post build command ends in a failure. Is there any way I can tell the POST_BUILD command depend on the previous custom command ?

Any suggestions ?

Thanks in advance, Surya

Deprived

Answer 1

Use add_custom_command's to create a file transformation chain

• *.(cxx|hxx) -> *_(cxx|hxx)_tro
• *_(cxx|hxx)_tro -> Foo.trx

and make the last transformation an first class entity in cmake by using add_custom_target. By default this target won't be build, unless you mark it with ALL or let another target that is built depend on it.

set(SOURCES foo.cxx foo.hxx)
add_library(Foo ${SOURCES})

set(trofiles)
foreach(_file ${SOURCES})
  string(REPLACE "." "_" file_tro ${_file})
  set(file_tro "${file_tro}_tro")
  add_custom_command(
    OUTPUT ${file_tro} 
    COMMAND perl ${CMAKE_CURRENT_SOURCE_DIR}/trans.pl ${CMAKE_CURRENT_SOURCE_DIR}/${_file} -o ${file_tro}
    DEPENDS ${_file}
  ) 
  list(APPEND trofiles ${file_tro})
endforeach()
add_custom_command(
  OUTPUT Foo.trx  
  COMMAND perl ${CMAKE_CURRENT_SOURCE_DIR}/combine.pl ${trofiles} -o Foo.trx
  DEPENDS ${trofiles}
)
add_custom_target(do_trofiles DEPENDS Foo.trx)
add_dependencies(Foo do_trofiles)

Kraal

Answer 2

You want to create a custom target that consumes the output of the custom commands. Then use ADD_DEPENDENCIES to make sure the commands are run in the right order.

This might be sort of close to what you want: https://gitlab.kitware.com/cmake/community/-/wikis/FAQ#how-do-i-use-cmake-to-build-latex-documents

Basically one add_custom_command for each file generated, collect a list of those files (trofiles), then use add_custom_target with a DEPENDS on the list trofiles. Then use add_dependencies to make the LibraryTarget depend on the custom target. Then the custom target should be built before the library target is built.

Andantino