是“全球"吗?makefile变量与特定于目标的变量不同吗? [英] Are "global" makefile variables distinct from target-specific variables?

问题描述

从文档:

出现在在目标范围内评估变量分配:因此，任何先前定义的特定于目标的变量值都将位于影响.请注意，此变量实际上与任何全局"变量不同值:两个变量不必具有相同的风格(递归与简单).

All variables that appear within the VARIABLE-ASSIGNMENT are evaluated within the context of the target: thus, any previously-defined target-specific variable values will be in effect. Note that this variable is actually distinct from any "global" value: the two variables do not have to have the same flavor (recursive vs. simple).

因此，给了一个makefile:

So, given a makefile:

% : foo += 1

all : x;

x ::
    @echo '$(foo)'

foo := 2

正在运行，我得到:

And running, I get:

2 1 1

仔细看一下上面的引用:

Taking a closer look at the quote above:

出现在在目标范围内评估变量分配.

All variables that appear within the VARIABLE-ASSIGNMENT are evaluated within the context of the target.

无法解释针对特定目标的定义如:% : foo += 1，最终会变成在其值中包括，即全局"(即非目标或特定于模式的值): 2 .

It is impossible to explain how a target-specific definition like: % : foo += 1, will end up to include in its value, the "global" (i.e. not target or pattern-specific) value: 2.

当我们稍后看时，在上面的引文中很难证明这一点:

Much harder to justify it, when we look later, in the quote above:

请注意，此变量实际上与任何全局"变量 不同 值:两个变量不必具有相同的风格(递归与简单).

Note that this variable is actually distinct from any "global" value: the two variables do not have to have the same flavor (recursive vs. simple).

如果，它们是不同的"，为什么 Make 最终会为目标 all 扩展，一个值是从全局"中提取的值的沙拉"，以及来自特定于目标的定义?

If, they are that "distinct", how come Make ends up expanding for the target all, a value that is a "salad" of values taken from the "global", and as well from the target-specific definition?

以及采用什么方法来产生值 2 1 1 ，因为显然，值 1 产生了值 2 在上面的makefile中.

And what methodology did Make use to bring about the value 2 1 1, because clearly, the value 1 proceeds the value 2 in the makefile above.

推荐答案

我相信您只是误解了"distinct"的含义.它不是两个变量.通过以下片段两个变量不必具有相同的风格"来阐明其含义.这才是重点.全局变量 foo 和特定于目标的变量 foo 是两个不同的变量(但在扩展时组合).

I believe you are simply misunderstanding what the meaning of "distinct" meant there. It did not mean that they are two different variables. The meaning was clarified by the following fragment "the two variables do not have to have the same flavor". That's the point. The global variable foo and the target-specific variable foo are two different (but combined when expanded) variables.

请记住，您得到的输出正是您所期望的.

With that in mind the output you get is exactly what you'd expect.

分配给 foo 的 first 是来自全局分配的值 2 .

The first thing assigned to foo is the value 2 from the global assignment.

仅在目标处理期间之后，处理 foo + = 1 赋值(两次，一次用于 all ，一次用于 x ).

Only after that, during the target processing, is the foo += 1 assignment processed (twice, once for all and once for x).

与您完全一样，这将使您 2 1 1 .

Which gets you 2 1 1 exactly as shown.

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