Gnu make: default values and conditionals

Applications Programming
1

I need some help.

I use variables and conditionals to build with or without specic libraries. I set

USEAL ?= 1 # get value from cmd, defaults to 1

(see comment)
the conditional is:

ifeq ($(USEAL),1)
    LIBS = <any libs>
else
    LIBS = 
endif

Its amazing that this works when invoked from the command line setting the variable to 1 explicit:

make USEAL=1

However when invoked without setting the variable

make

it doesn't work.
I already defined a test target to print USEAL's default value, which is 1.

It looks like 1 != 1

any idea?

2

In what way does it "not work"? What actually happens?

3

USEAL's default value is 1, nevertheless it ignores it as if USEAL's default value would be 0, unless I invoke with USEAL=1.

4

I've tested it with this Makefile:

USEAL ?= 1

ifeq ($(USEAL),1)
    LIBS = qwertyuip
else
    LIBS =
endif

all:
        echo $(LIBS)

$ make
echo qwertyuip
qwertyuip

$ make USEAL=0
echo

$ make USEAL=1
echo qwertyuip
qwertyuip

$

Seems to work. The problem may be elsewhere, if there's anything to your makefile you haven't posted yet.

5

Thanks a lot!
I did the same job. Then I carefully copied all the working lines from the test makefile into the real one et voila: it works. The only real difference is that the

VARIABLE ?= DEF.VAL

now is located at the beginning of the makefile, whereas before it was placed somewhat in the middle part.

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