[CMake] Build rule for specific file extension

Michael Wild themiwi at gmail.com
Fri Jun 25 08:22:59 EDT 2010

On 25. Jun, 2010, at 13:26 , Mathias Lafeldt wrote:

> Hi,
> is there a way to tell CMake how to "compile" files based on their
> extension?
> For example, here's a make rule to build an object file from a *.lst file:
> %.o : %.lst
>    echo "#include \"irx_imports.h\"" > build-imports.c
>    cat $< >> build-imports.c
>    $(IOP_CC) $(IOP_CFLAGS) build-imports.c -o $@
>    -rm -f build-imports.c
> How can I convert this to CMake? I considered using add_custom_target,
> but I don't know how to apply it to all files with the same extension.
> -Mathias

No, there is no way to do this. Regrettable as it is, I also think that there are probably pretty good reasons for not providing such a facility. The usual thing to do is to write a function which loops over all the input files, creates a custom command for each of the files and then returns the list of the products in a variable. E.g.

find_program(FOO_EXECUTABLE foo)
function(preprocess_foo out_var)
  foreach(in_f ${ARGN})
    set(out_f "${CMAKE_CURRENT_BINARY_DIR}/${out_f}")
    add_custom_command(OUTPUT ${out_f}
      COMMAND ${FOO_EXECUTABLE} -o ${out_f} ${in_f}
      DEPENDS ${in_f}
      COMMENT "Creating preprocessed foo file ${out_f}"
    list(APPEND result ${out_f})
  set(${out_var} "${result}" PARENT_SCOPE)

preprocess_foo(prep_files a.foo b.foo c.foo)
add_executable(bar ${prep_files})



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