Makefile find in array

Question

If I have something like this:

PROJECTS += path/to/first
PROJECTS += path/to/second
PROJECTS += path/to/third

and

LIBS += lib_output/first.lib
LIBS += lib_output/second.lib
LIBS += lib_output/third.lib

How could I associate the project from PROJECTS += path/to/first with LIBS += lib_output/first.lib? Is there something like a hashmap available in a makefile? Or possibility to search in an array?

Make isn't really good at complex variables. Could you give us a better idea of what you're trying to do? — Beta
– Beta, Commented Sep 2, 2011 at 12:44

Maxim Egorushkin · Accepted Answer · 2011-09-04 15:22:20Z

14

You can simulate lookup tables using computed variable names and the fact that make variable names can include some special characters like dot and forward slash:

PROJECTS += path/to/first
PROJECTS += path/to/second
PROJECTS += path/to/third

LIBS += lib_output/first.lib
LIBS += lib_output/second.lib
LIBS += lib_output/third.lib

lookup.path/to/first  := lib_output/first.lib
lookup.path/to/second := lib_output/second.lib
lookup.path/to/third  := lib_output/third.lib

path := path/to/first
$(info ${path} -> ${lookup.${path}})
path := path/to/second
$(info ${path} -> ${lookup.${path}})
path := path/to/third
$(info ${path} -> ${lookup.${path}})

Outputs:

$ make
path/to/first -> lib_output/first.lib
path/to/second -> lib_output/second.lib
path/to/third -> lib_output/third.lib

edited Sep 4, 2011 at 15:22

answered Sep 2, 2011 at 14:34

Maxim Egorushkin

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8 Comments

user377178 Over a year ago

can you use it in a rule? I have rules like foo.o: randompath/foo.c, I have plenty of such files under various path, I can generate object names easily $(notdir $(SOURCES:.c=.o)), but then I cannot derive source name in pattern rule. Can I use your solution to create a single rule for them all?

Maxim Egorushkin Over a year ago

You can try using VPATH to help make locate the sources from different directories. A better solution is to replicate the source directory hierarchy in the object directory. That would avoid filename clashes.

user377178 Over a year ago

Good pointer. I think vpath (lowercase) is what I need. My object file name is actually 'flattened' path, e.g. some_5_steps_deep_path_foo.c.o. Much more efficient than replicating folder structure if you only cherry pick few files from each of bunch of projects.

Mohammad Azim Over a year ago

@MaximEgorushkin is there a way to do this expansion in dependency place. Like: target: $(lookup.$(path)) I find that it does not get evaluated.

Maxim Egorushkin Over a year ago

@MohammadAzim There is, it is called Secondary Expansion.

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eriktous · Accepted Answer · 2011-09-04 19:16:14Z

2

I'm not sure if I completely understand your question, but I think the word function might be what you need (it may be a GNU make extension):

$(word 2, $(PROJECTS)) returns path/to/second,
$(word 2, $(LIBS)) returns lib_output/second.lib.

answered Sep 4, 2011 at 19:16

eriktous

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