Why isn't my eval function in my Makefile working?

问题

When I try to run the following make file (updated with suggestions below):

# Build Directories
src_dir=src
obj_dir=obj
bin_dir=bin

cc=cl
cc_flags=

configs = dbg rel

# create the directory for the current target.
dir_guard=@mkdir -p $(@D)

# source files
src = MainTest.cpp

define build_template = 
# object files - replace .cpp on source files with .o and add the temp directory prefix
obj_$(1) = $$(addprefix $$(obj_dir)/$(1)/, $$(addsuffix .obj, $$(basename $$(src))))

testVar = "wooo"

# build TwoDee.exe from all of the object files.
$$(bin_dir)/$(1)/MainTest.exe : $$(obj_$(1))
    $$(dir_guard)
    $$(cc) -out:$$@ $$(obj_$(1)) -link

# build all of the object files in the temp directory from their corresponding cpp files.
$$(obj): $$(obj_dir)/$(1)/%.obj : $$(src_dir)/%.cpp
    $$(dir_guard)
    $$(cc) $$(cc_flags) -Fo$$(obj_dir)/$$(1) -c $$<
endef

$(foreach cfg_dir,$(configs),$(eval $(call build_template,$(cfg_dir))))

release: $(bin_dir)/rel/MainTest.exe

debug: cc_flags += -Yd -ZI
debug: $(bin_dir)/dbg/MainTest.exe

$(warning testVar $(testVar))

All I get is:

$ make
Makefile:41: testVar
make: *** No rule to make target `bin/rel/MainTest.exe', needed by `release'.  Stop.

You can see from the output that the testVar variable is never set. I made these changes based on my last question: Why doesn't my makefile target-specific variable work?

回答1:

There are some spaces which confuse Make. Try this:

$(foreach cfg_dir,$(configs),$(eval $(call build_template,$(cfg_dir))))

Also make sure that you specify the right objects to link:

    $$(cc) -out:$$@ $$(obj_$(1)) -link

And as @Beta pointed out in the comments below, the = in the template definition syntax requires GNU make 3.82 or later. So better omit it from the line:

define build_template

来源：https://stackoverflow.com/questions/11332523/why-isnt-my-eval-function-in-my-makefile-working