Make - 没有什么可做的 - 只有文件扩展名

Question

我有一个简单的c程序 - hello_world.c

你可以通过文件名来判断我对c非常新.

我希望编译以下内容:

make hello_world.c

但这会给出一条错误消息: make: Nothing to be done for hello_world.c.

如果我只是这样做make hello_world,即没有扩展名.

有人可以解释为什么会这样吗？

Answer 1

make以目标为参数.如果你告诉它你要做hello_word.c,它会看,看到该文件已经存在并且没有依赖关系,并且将决定它是最新的 - 因此无关.

当你说make hello_world,make查找hello_word,找不到它,然后查找hello_world.o,找不到它,然后查找hello_world.c,找到它,然后使用它的隐式规则从中构建hello_world.

您可以make -d用来查看make正在制定的决策.这是一个例子make hello_world.c- 我已经整理了一堆来展示最后一部分,这是你关心的:

...
Considering target file `hello_world.c'.
 Looking for an implicit rule for `hello_world.c'.
 ...
 No implicit rule found for `hello_world.c'.
 Finished prerequisites of target file `hello_world.c'.
No need to remake target `hello_world.c'.
make: Nothing to be done for `hello_world.c'.

然后,为make hello_world:

...
Considering target file `hello_world'.
 File `hello_world' does not exist.
 Looking for an implicit rule for `hello_world'.
 Trying pattern rule with stem `hello_world'.
 Trying implicit prerequisite `hello_world.o'.
 Trying pattern rule with stem `hello_world'.
 Trying implicit prerequisite `hello_world.c'.
 Found an implicit rule for `hello_world'.
  Considering target file `hello_world.c'.
   Looking for an implicit rule for `hello_world.c'.
   Trying pattern rule with stem `hello_world'.
   ...
   No implicit rule found for `hello_world.c'.
   Finished prerequisites of target file `hello_world.c'.
  No need to remake target `hello_world.c'.
 Finished prerequisites of target file `hello_world'.
Must remake target `hello_world'.
cc     hello_world.c   -o hello_world
...
Successfully remade target file `hello_world'.