[CMake] Link in object files generated by another tool

[Hugo Heden]

2008/11/24 James Bigler <jamesbigler at gmail.com>:
> Is it possible to link in an object file generated by another tool?
>
> I want to create a custom command that generates an object file that I
> could then link into a library or executable later.
>
> Is this possible from CMake?
>

An example follows. The ADD_CUSTOM_COMMAND that you may be looking for
is at the bottom.


SET( EXPAT_DIR_STRING expat-2.0.1 )

SET( expat_fpic_object_files
  ${CMAKE_CURRENT_BINARY_DIR}/${EXPAT_DIR_STRING}/lib/.libs/xmlparse.o
  ${CMAKE_CURRENT_BINARY_DIR}/${EXPAT_DIR_STRING}/lib/.libs/xmlrole.o
  ${CMAKE_CURRENT_BINARY_DIR}/${EXPAT_DIR_STRING}/lib/.libs/xmltok.o
)

ADD_LIBRARY(
  expat
  STATIC
  EXCLUDE_FROM_ALL
  ${expat_fpic_object_files}
)

SET_SOURCE_FILES_PROPERTIES(
  ${expat_fpic_object_files}
  PROPERTIES
  EXTERNAL_OBJECT true # to say that "this is actually an object file,
so it should not be compiled, only linked"
  GENERATED true       # to say that "it is OK that the obj-files do
not exist before build time"
  )

SET_TARGET_PROPERTIES(
  expat
  PROPERTIES
  LINKER_LANGUAGE C # Or else we get an error message, because cmake
can't figure out from the ".o"-suffix that it is a C-linker we need.
  ARCHIVE_OUTPUT_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}/lib
  )


ADD_CUSTOM_COMMAND(
  OUTPUT
    ${expat_fpic_object_files}
  WORKING_DIRECTORY  ....
  COMMAND  ....# Some tool
  COMMAND  ....# Some tool