Question

As the title, in makefile GNU, what is the diff between obj_$(variable) and $(addprefix “obj_”, $(variable)). I am sure there is the difference, because the first one can be compared to a string, and the latter one cannot be recognized as a string. Please let me know if I am wrong. I want to make the second one work as a string, so I can use $($(addprefix “obj_”, $(variable))) as a variable (now it doesn’t work).

Thank you guys.

Answer 1

Test it by yourself:

print_values = \
    $(warning Let the value of '$$(variable)' to be [$(variable)]) \
    $(warning then the value of obj_$$(variable) is [obj_$(variable)]) \
    $(warning $$(addprefix  "obj_", $$(variable)) is [$(addprefix "obj_", $(variable))]) \
    $(warning )

variable := foo
$(print_values)

variable := foo bar baz
$(print_values)

variable :=
variable += foo
$(print_values)

You will get the following output:

makefile:10: Let the value of '$(variable)' to be [foo]
makefile:10: then the value of obj_$(variable) is [obj_foo]
makefile:10: $(addprefix  "obj_", $(variable)) is ["obj_"foo]
makefile:10: 
makefile:13: Let the value of '$(variable)' to be [foo bar]
makefile:13: then the value of obj_$(variable) is [obj_foo bar]
makefile:13: $(addprefix  "obj_", $(variable)) is ["obj_"foo "obj_"bar]
makefile:13: 
makefile:17: Let the value of '$(variable)' to be [ foo]
makefile:17: then the value of obj_$(variable) is [obj_ foo]
makefile:17: $(addprefix  "obj_", $(variable)) is ["obj_"foo]
makefile:17: 

P.S. As I told you in the answer to another your question, quotes are definitely not what you want.

Use plain obj_:

$(addprefix obj_,$(variable))

Instead of:

$(addprefix "obj_",$(variable))