从Makefile中的C ++ FLAGS删除标志? [英] Remove a flag from C++FLAGS in Makefile?

问题描述

我有一个Makefile，其中包含另一个设置很多默认值的makefile.我无法编辑包含的生成文件，即使在包含的生成文件中设置了C ++ FLAGS的值，我也想更改其值.具体来说，每当debug = 1时，我都希望从C ++ FLAGS中删除优化标志.

I've got a Makefile that includes another makefile that sets a lot of defaults. I can't edit the included makefile and I'd like to change the value of C++FLAGS in my makefile even though it is set in the included makefile. Specifically, I'd like to remove the optimization flag from C++FLAGS whenever debug=1.

我尝试了以下操作:

C++FLAGS=$(filter-out -O3,$(C++FLAGS))

哪个失败并出现以下错误:

Which fails with the following error:

Recursive variable `C++FLAGS' references itself (eventually).  Stop.

似乎可以做这样的事情，有人知道秘密吗?

It seems like doing something like this should be possible, anybody know the secret?

推荐答案

C++FLAGS:=$(filter-out -O3,$(C++FLAGS))

:=赋值立即评估右值，因此应该可以正常工作.另一方面，=具有延迟的扩展语义(即，只要使用左值，C++FLAGS就会扩展，从而导致递归).

The := assignment immediately evaluates the rvalue and this should therefore work. = on the other hand has delayed expansion semantics (i.e. the C++FLAGS will expand whenever the lvalue gets used, which leads to recursion).

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