延迟或重复GNU make中的先决条件

问题描述

我试图将我的Subversion版本号嵌入C ++项目中，并且在设置GNU make这样做时遇到问题.我的makefile当前看起来像这样:

I'm trying to embed my Subversion revision number in a C++ project and am having problems setting up GNU make to do so. My makefile currently looks something like this:

check-svnversion:
  ../shared/update-svnversion-h.pl

../shared/svnversion.h: check-svnversion

shared/svnversion.o: ../shared/svnversion.h

.PHONY: check-svnversion

svnversion.o 取决于 svnversion.cpp (通过模式规则)和 svnversion.h (明确列出，因为依赖项检查不是)t由于某种原因将其捡起). svnversion.h 是由 update-svnversion-h.pl 脚本创建和维护的(该脚本基本上只运行 svnversion 并将其输出为C ++文件).

svnversion.o depends on svnversion.cpp (via a pattern rule) and svnversion.h (listed explicitly because dependency checking isn't picking it up for some reason). svnversion.h is created and maintained by the update-svnversion-h.pl script (which basically just runs svnversion and munges the output into a C++ file).

当前，我必须运行两次 make 才能使文件保持最新状态.第一次， make 运行 update-svnversion-h.pl (因为它已被列为先决条件)，但不检查 svnversion.h的时间戳 update-svnversion-h.pl 对其进行了更改，因此它不会重新制作 svnversion.o .第二次，它确实检查时间戳，无论如何都运行 update-svnversion-h.pl (由于 svnversion.h 日期)，然后重新编译 svnversion.cpp 以创建 svnversion.o .

Currently, I have to run make twice to get the file up to date. The first time, make runs update-svnversion-h.pl (since it's listed as a prerequisite) but does not check the timestamp of svnversion.h afterwards to see that it was changed by update-svnversion-h.pl, so it does not remake svnversion.o. The second time, it does check the timestamp, runs update-svnversion-h.pl anyway (which doesn't do anything this time, since svnversion.h is up to date), then recompiles svnversion.cpp to make svnversion.o.

是否有一种方法可以告诉GNU make对一个必备组件进行两次评估，或者延迟检查必备组件的时间戳，直到该必备组件的命令执行完毕?

Is there a way to tell GNU make to evaluate a single prerequisite twice or to delay checking the timestamp on a prerequisite until after that prerequisite's commands are finished?

或者，是否有更好的方法在我的源代码中嵌入修订号?(为了提高速度，我正在尝试避免在每次构建时都需要重新编译的解决方案.)

Alternatively, is there a better way to embed a revision number in my source code? (For the sake of speed, I'm trying to avoid solutions that would require recompilation on every build.)

推荐答案

我通过使我的check-svnversion规则删除svnversion.o来解决此问题，以便在需要时强制对其进行重新编译.这并不完全优雅，但可以正常工作.它看起来与 CesarB的答案.

I solved this by having my check-svnversion rule delete svnversion.o to force it to be recompiled if needed. This isn't exactly elegant, but it works; it looks similar to the autotools solution described in CesarB's answer.

../shared/svnversion.h: check-svnversion

check-svnversion:
    ../shared/update-svnversion-h.pl
    @#Force recreation of svnversion.o.  Otherwise, make won't notice that
    @#svnversion.h has changed until the next time it's invoked.
    @if [ ../shared/svnversion.h -nt shared/svnversion.o ] ; then rm shared/svnversion.o ; fi

shared/svnversion.o: ../shared/svnversion.h

.PHONY: check-svnversion

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