On 06/28/2010 05:24 AM, Tom Birch wrote: > CMake's dependency scanner uses its own parser to scan for #include > directives, and then builds up the dependency tree this way. I know it's > possible to rig up an invocation of gcc -M to generate the correct > dependencies, and then feed this into the OBJECT_DEPENDS property of source > files, but that means that dependency generation would happen when running > 'cmake .', not 'make'.
One compelling reason why dependency scanning is delayed until building time is that it's taking dynamically generated files into account, i.e. files not being present at configuration time. Look at the following CMakeLists.txt: CMAKE_MINIMUM_REQUIRED(VERSION 2.8 FATAL_ERROR) PROJECT(DYNDEP C) FILE(WRITE ${CMAKE_BINARY_DIR}/f.h "void f(void);\n") FILE(WRITE ${CMAKE_BINARY_DIR}/f.c "\#include \"f.h\"\nvoid f(){}\n") FILE(WRITE ${CMAKE_BINARY_DIR}/main.c.in "\#include \"f.h\"\nint main(void){f(); return 0;}\n" ) ADD_CUSTOM_COMMAND( OUTPUT main.c COMMAND cp main.c.in main.c DEPENDS ${CMAKE_BINARY_DIR}/main.c.in ) INCLUDE_DIRECTORIES(".") ADD_EXECUTABLE(main ${CMAKE_BINARY_DIR}/main.c ${CMAKE_BINARY_DIR}/f.c) After cmaking, when running make, the dependency of main.c.o on f.h is figured out, and this couldn't be achieved during the configuration as main.c doesn't exist at that time. > I guess the bigger question here is: why doesn't cmake use gcc -M internally > when it's available? It's vastly superior to any homegrown parser, so why not > use it? My assumption is: As gcc or other tools for dependency scanning like makedepend are not available or desired on all systems supported by CMake there's a need for an in-house solution, at least as fallback, and if you once have to provide such a solution why not using it thoroughly? Besides, this reduces the dependencies on external programs - one of CMake's strengths. Regards, Michael _______________________________________________ Powered by www.kitware.com Visit other Kitware open-source projects at http://www.kitware.com/opensource/opensource.html Please keep messages on-topic and check the CMake FAQ at: http://www.cmake.org/Wiki/CMake_FAQ Follow this link to subscribe/unsubscribe: http://www.cmake.org/mailman/listinfo/cmake