问题描述
我正在读取Qt创建的项目的makefile，该文件具有以下内容:
I am reading a makefile for a Qt-created project that has the following:
{backend}.cpp{release\}.obj::
$(CXX) -c $(CXXFLAGS) $(INCPATH) -Forelease\ @<<
$<
<<
(以上代码将\ t用于配方，并与makefile相同)
这条规则和食谱都使我感到困惑.
Both the rule and the recipe confuse me.
我将从规则中的{backend}开始.显然，对于{release}也是一样.我假设这是对名为backend的特定子目录的引用.我想..\backend\release\bar.obj将被视为合法目标?但是 make 的哪一部分说这是合法的语法，这到底发生了什么?
I'll start with {backend} in the rule. Obviously the same confusion for {release} as well. I assume this is a reference to a particular sub-directory named backend. I guess that ..\backend\release\bar.obj would be found as a legitimate target? But what part of make says this is legitimate syntax and what exactly happens here?
FWIW:这是在一节中注释为:##### implicit rules.版本:GNU Make 4.2.1 Built for x86_64-unknown-cygwin
FWIW: This is in a section commented as: ##### implicit rules.Version: GNU Make 4.2.1 Built for x86_64-unknown-cygwin
奖励积分:
说明食谱中@<<和<<的用法...(是的，我缺乏bash shell技巧... ).这是否引用$<的第一个先决条件并以静默方式重定向它?为什么不是$$<?
Explain the use of @<< and << in the recipe... (Yes, I'm lacking in bash shell finesse...). Is this referencing the first prerequisite with $< and silently redirecting it? Why isn't it $$<?
谢谢.
推荐答案
这是NMAKE批处理模式规则
That is an NMAKE batch-mode rule
https://docs .microsoft.com/en-us/cpp/build/batch-mode-rules?view = vs-2017
等效的GNU Make规则类似于
The equivalent GNU Make rule would be something like
backend/%.obj: release/%.cpp:
顾名思义，这些规则将仅对所有有效目标调用一次配方，并期望该规则通过$<宏一次创建所有目标.
With the difference that, as the name suggests, these rules will invoke their recipes only once for all valid targets and expect the rule to create all of the targets in a single pass with the $< macro.
<<语法是NMAKE的内联文件功能
The << syntax is NMAKE's inline file feature
https ://docs.microsoft.com/zh-CN/cpp/build/inline-files-in-a-makefile?view = vs-2017
这将展开并捕获尖括号之间的所有内容，并将其保存到文件中，在这种情况下，这是一个临时文件，因为在括号后未指定文件名.然后，文件通过 @ 选项.
This expands and captures everything between the angle brackets and saves it to a file, in this case a temporary file as no filename is specified after the brackets. The file is then passed to the compiler as a response file on the first line of the recipe through the @ option.
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