targets in subdirectories

[kilgore trout]

Greetings,

 

I am using gmake via Msys on a win xp box.

The project that I am trying to build, has a 'build_dir' off of the root of the project tree which is where I am to keep all the object files.  I am having a problem writing a rule that will correctly detect if that file is missing/up-to-date.  I have, for example:

 

BUILD_DIR=$(PROJ_ROOT)/build_dir

 

$(BUILD_DIR)/%.o : %.c

    mkdir -p $(BUILD_DIR)

    $(CC) $(CFLAGS) $< -o $@

    mv $@ $(BUILD_DIR)

 

but it will build if the .o files are missing from the local dir, and then not copy to the build_dir.

If I remove the $(BUILD_DIR) from the rule, it will always rebuild the .o files, and copy them.

 

What am I missing?  Can I not include a path in a target rule?  How can I (properly) do this?

 

Any and all help appreciated!

 

-kt.