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I have this makefile target that contains these steps:

...
cd $(GRAPHICS_BUILD_DIR)
clang++ -c -I$(SFML_HEADERS) $(GRAPHICS_DIR)/*.cpp
cd $(BASE_DIR)
...

For some reason, Clang outputs the build files into BASE_DIR, not GRAPHICS_BUILD_DIR. Everything compiles fine, and when I execute one line at a time manually, it works fine, and the *.o files are outputted in the correct directory.

Why doesn't make put these files in the correct directory, and how can I force it to?

I'm using clang3.1 and the current version of GNUMake on ubuntu linux kernel 3.2.0-26.

jepugs
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  • To specify the output file to produce you can pass the `-o ...` flag to clang. E.g. `clang++ -c -I$(SFML_HEADERS) $(GRAPHICS_DIR)/$(FILE).cpp -o $(GRAPHICS_BUILD_DIR)/$(FILE).o` Although it does seem to me that `cd`ing to the output directory in your script should cause the files to be in that output directory by default. – bames53 Jul 02 '12 at 17:45
  • @bames53: I can't pass the -o flag because I'm compiling multiple files. – jepugs Jul 02 '12 at 18:04
  • Yeah, that's why I didn't put it as an answer. You probably shouldn't be building like that though. Usually makefiles have library and executable targets that explicitly list out what object files they depend on, and then there's a generic rule for building an object file. Among other things this allows for fast partial rebuilds based on the dependency graph, and it allows you to explicitly specify the output file with the `-o` flag. – bames53 Jul 02 '12 at 18:46
  • I guess I need to learn more about make then. *groan*. I was trying to do this the lazy way. Thank you very much for the answer though. – jepugs Jul 02 '12 at 20:10
  • Take a look at the last makefile shown [here](http://mrbook.org/tutorials/make/). That should give you the basic idea. (Although all targets in a makefile ought to have the makefile itself as a dependency as well.) – bames53 Jul 02 '12 at 20:23

1 Answers1

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The trouble is that in a Make rule, each command executes in its own subshell; nothing is remembered from one line to the next. So your first command starts in $(BASE_DIR), moves into $(GRAPHICS_BUILD_DIR), and dies. Your second command starts in $(BASE_DIR) and runs Clang there.

Try this:

...
cd $(GRAPHICS_BUILD_DIR) ; clang++ -c -I$(SFML_HEADERS) $(GRAPHICS_DIR)/*.cpp
...
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