使用GNU make创建几个预编译的头文件

问题描述

我使用gcc(以g++运行)和GNU make.我使用gcc预编译头文件precompiled.h，创建precompiled.h.gch； Makefile中的以下行可以做到这一点:

I use gcc (running as g++) and GNU make.I use gcc to precompile a header file precompiled.h, creating precompiled.h.gch; the following line in a Makefile does it:

# MYCCFLAGS is a list of command-line parameters, e.g. -g -O2 -DNDEBUG
precompiled.h.gch: precompiled.h
    g++ $(MYCCFLAGS) -c $< -o $@

一切都很好，直到我不得不使用不同的命令行参数运行g++为止.在这种情况下，即使precompiled.h.gch存在，也无法使用它，并且编译速度会慢得多.在gcc文档中，我已阅读到可以解决这种情况的信息，我必须创建一个名为precompiled.h.gch的目录并放入那里的预编译头文件，每一组g++命令行参数一个文件.

All was well until i had to run g++ with different command-line parameters.In this case, even though precompiled.h.gch exists, it cannot be used, and the compilation will be much slower.In the gcc documentation i have read that to handle this situation,i have to make a directory called precompiled.h.gch and putthe precompiled header files there,one file for each set of g++ command-line parameters.

所以现在我想知道如何更改我的Makefile来告诉g++创建gch文件以这种方式.也许我可以运行g++只是为了测试它是否可以使用任何现有文件在precompiled.h.gch目录中，如果没有，则生成一个具有唯一文件名的新的预编译头文件.

So now i wonder how i should change my Makefile to tell g++ to createthe gch-files this way.Maybe i can run g++ just to test whether it can use any existing filein the precompiled.h.gch directory,and if not, generate a new precompiled header with a unique file name.

gcc是否支持进行此类测试?

Does gcc have support for doing such a test?

也许我可以用另一种方式实现我想要的东西?

Maybe i can implement what i want in another way?

推荐答案

回答我自己的问题似乎很奇怪.无论如何，这里去.

It seems weird to answer my own question; anyway, here goes.

要检测是否存在合适的预编译头文件，请在头文件中添加一个故意的错误:

To detect whether a suitable precompiled header file exists, i add a deliberate error to my header file:

// precompiled.h
#include <iostream>
#include <vector>
...
#error Precompiled header file not found

之所以可行，是因为如果gcc找到了预编译的标头，它将不会读取.h文件，也不会遇到错误.

This works because if gcc finds a precompiled header, it will not read the .h file, and will not encounter the error.

要编译"这样的文件，请先消除错误，然后将结果放在一个临时文件中:

To "compile" such a file, i remove the error first, placing the result in a temporary file:

grep -v '#error' precompiled.h > precompiled.h.h
g++ -c -x c++ $(MYCCFLAGS) precompiled.h.h -o MORE_HACKERY

此处MORE_HACKERY不仅是纯文件名，还包含一些代码来制作具有唯一名称(mktemp)的文件.为了清楚起见，将其省略.

Here MORE_HACKERY is not just a plain file name, but contains some code to make a file with unique name (mktemp). It was omitted for clarity.

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