automake：修改隐式 make 规则以包含额外的标志
如何添加适用于所有 makefile 的额外标志变量（如 CPPFLAGS）？目前，我们正在使用 CPPFLAGS，但它应该保留为用户变量，我想保留它。我不想使用 AM_CPPFLAGS，因为我想为特定的 Makefile.amS 保留它。我想要的是像 GLOBAL_CPPFLAGS 这样的东西，我可以在configure.ac中设置它并将其应用于所有内容。如果有一种方法可以显式忽略该标志，那就太好了。
我认为我需要做的是编写自己的 make 规则，但是如何使其在所有子文件夹中可用而不将其复制到每个 Makefile.am 中？
How can I add extra flag variables (like CPPFLAGS) that will apply to all makefiles? Currently, we're using CPPFLAGS, but that is supposed to be reserved as a user variable and I would like to reserve it. I'd prefer not to use AM_CPPFLAGS because I would like to reserve that for specific Makefile.amS. What I want is something like GLOBAL_CPPFLAGS that I could set in configure.ac and have it applied to everything. It would also be nice if there were a way to explicitly ignore the flag.
I think what I need to do is to write my own make rule, but how would I make that available in all subfolders without copying it into every Makefile.am?
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您不使用 CPPFLAGS 是正确的。这是一个用户变量。我要做的是这样的：
在源目录的根目录中，创建一个名为
common.am的文件，并在其中定义您需要的任何内容：我知道您说过您不想使用
AM_CPPFLAGS，但请听我说完。在您的各个子目录中，include $(top_srcdir)/common .am并根据需要扩展或覆盖AM_CPPFLAGS：如果要覆盖，请使用
=而不是+=>：You're correct in not using
CPPFLAGS. That's a user variable. What I'd do is something like this:In the root of your source dir, create a file called
common.amand define whatever you need in there:I know you said you didn't want to use
AM_CPPFLAGS, but hear me out. In your individual subdirectories,include $(top_srcdir)/common.amand extend or overrideAM_CPPFLAGSas needed:If you want to override, use
=instead of+=:我想你回答了你自己的问题：你必须将新规则复制到每个 makefile 中。
I think you answered your own question: you will have to copy the new rule into every makefile.
CPPFLAGS 是您可能应该使用的机制。只需在 configure.ac 中的某个位置连接您想要的标志：
GLOBAL_CPPFLAGS="-DSOMETHING"
...
CPPFLAGS="$CPPFLAGS $GLOBAL_CPPFLAGS"
就可以设置了。
CPPFLAGS is the mechanism you probably should be using. Just concatenate the flags you want somewhere in configure.ac:
GLOBAL_CPPFLAGS="-DSOMETHING"
...
CPPFLAGS="$CPPFLAGS $GLOBAL_CPPFLAGS"
and you should be set.