makefile，obj _ $（variable）和$（addprefix「obj_」，$（variable））之間的差異是什麼

Question

作爲標題，在makefile GNU中，obj _ $（變量）和$（addprefix「obj_」，$（variable））。我確定有區別，因爲第一個可以與字符串進行比較，後一個不能被識別爲字符串。如果我錯了，請讓我知道。我想讓第二個字符串工作，所以我可以使用$（$（addprefix「obj_」，$（variable）））作爲變量（現在不起作用）。

謝謝你們。

Answer 1

測試它自己：

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) 

您將得到以下輸出：

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: 

附：正如我告訴過你the answer到另一個你的問題，報價絕對不是你想要的。

使用純obj_：

$(addprefix obj_,$(variable)) 

相反的：

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