问题描述
在运行依赖于生成文件的目标时，我对Make的行为有疑问.
I have a question regarding the behavior of Make when running targets that are dependent on generated files.
考虑到下面的源代码树和Makefile，即使我在第一次运行时生成了所有内容，当我运行它时也需要两次运行才能完成构建".
Given the source tree and Makefile below, when I run this it takes two runs to complete the "build" even though everything was generated on the first run.
$ ls -R
.:
bar foo Makefile
Makefile
all: foobar
work:
mkdir -p work
work/foo: work foo
cp foo work/foo
work/bar: work bar
cp bar work/bar
foobar: work/foo work/bar
make
$ make
mkdir -p work
cp foo work/foo
cp bar work/bar
$ ls -R
.:
work/ bar CMakeLists.txt foo Makefile
./work:
bar foo
$ make
cp foo work/foo
$ make
make: Nothing to be done for 'all'.
为什么会这样?
推荐答案
您需要将目录设置为 仅订购 的先决条件，否则每次目录更改时都将重新建立目标；在第二次调用期间，work比work/foo更新，因为work/bar是在work/foo之后创建的，所以work的时间戳比work/foo更新.
You need to make the directory an order-only prerequisite, otherwise the targets will be remade each time the directory changes; during the second invocation work is newer than work/foo because work/bar was created after work/foo, so work's timestamp is newer than work/foo.
work/foo: foo | work
cp foo work/foo
work/bar: bar | work
cp bar work/bar
或更简洁
work/foo work/bar: work/%: % | work
cp $< $@
这篇关于Makefile目标对生成文件的依赖的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！