Makefile-使用修改后的头文件进行重建

问题描述

在我的项目中，我有一些包含方法的头文件(例如，用于模板类).所有这些头文件都包含在单个文件header.h中，然后每个cpp文件中都包含.这样，我必须只在一个地方更改代码.还有一些.h文件，但没有相应的.cpp文件.
然后我有这个makefile:

In my project I have some header files which contain methods (e.g. for template classes). All these header files are included in a single file header.h, which is then included in every cpp file. This way, I have to change the code just in one place. There are also some .h files without a corresponding .cpp file.
Then I have this makefile:

# Makefile

.PHONY: run clean rebuild

CC     = g++
CFLAGS = -Wall -Ofast -std=c++0x -pthread
RM     = rm -f
EXEC   = main

SRC    = $(wildcard *.cpp)
OBJ    = $(SRC:.cpp=.o)

$(EXEC): $(OBJ)
    $(CC) $(CFLAGS) -o $@ $(OBJ)

%.o: %.cpp
    $(CC) $(CFLAGS) -c $^

run: $(EXEC)
    ./$(EXEC)

clean:
    $(RM) $(EXEC) *.o *.gch *~

rebuild: clean $(EXEC)

一切正常，除了一个小的但令人讨厌的细节:如果我修改cpp文件，那么我可以做make并且一切都正确更新了，但是如果我修改了头文件，那么我必须删除所有内容并重新编译从头开始(这就是为什么我有这个丑陋的rebuild目标的原因)，否则编辑将无效.

Everything works fine, except for one small but annoying detail: if I modify a cpp file, then I can do make and everything is updated correctly, but if I modify a header file then I have to remove everything and recompile from scratch (and this is the reason why I have that ugly rebuild target), otherwise the edit will have no effect.

有没有一种方法可以使情况更好，而无需重新构建整个代码?

Is there a way to make things better without restructuring the entire code?

我尝试了这个Makefile

I tried with this makefile

.PHONY: run clean rebuild

CC     = g++
CFLAGS = -Wall -Ofast -std=c++0x -pthread
RM     = rm -f
EXEC   = main

SRC    = $(wildcard *.cpp)
OBJ    = $(SRC:.cpp=.o)

$(EXEC): $(OBJ)
    $(CC) $(CFLAGS) -o $@ $(OBJ)

%.o: %.cpp headers.h
    $(CC) $(CFLAGS) -c $<

run: $(EXEC)
    ./$(EXEC)

clean:
    $(RM) $(EXEC) *.o *.gch *.d *~

rebuild: clean $(EXEC)

但是结果不是我想要的:如果我修改一个头文件并执行make，它告诉我目标是最新的，而我希望重新编译它.

but the result is not what I want: if I modify a single header file and the do make, it tells me that the target is up to date, while I would like it to be recompiled.

推荐答案

假设您有foo.cpp，其中包含以下行:

Suppose you have foo.cpp, which contains the line:

#include "bar.h"

您的通用规则:

%.o: %.cpp
    $(CC) $(CFLAGS) -c $^

修改bar.h(并要求使用foo.o)时，

不会重建foo.o.如果您对foo.o有一个附加规则，它将起作用:

will not rebuild foo.o when bar.h has been modified (and foo.o is called for). It would work if you had an additional rule for foo.o:

%.o: %.cpp
    $(CC) $(CFLAGS) -c $<  # note the change of automatic variable

foo.o: bar.h

手工编写这样的规则会很痛苦，但是g ++会帮您做到这一点:

Writing such rules by hand would be a pain, but g++ will do it for you:

%.o: %.cpp
    $(CC) $(CFLAGS) -c -MMD $<

此命令将生成文件foo.d(作为构建foo.o的副作用)，该文件包含以下行:

This command will produce the file foo.d (as a side effect of building foo.o) which contains the line:

foo.o: bar.h

在单独的文件中包含该行对您有什么好处?您可以像下面这样用一行(在makefile的末尾)将其拉入makefile:

What good does it do you, having that line in a separate file? You can pull it into the makefile with a line (at the end of the makefile) like this:

-include *.d

(如果这种方法看起来非常简单，那是因为很多聪明的人投入了很多思想.)

(If this approach seems amazingly simple, that's because a lot of smart people put a lot of thought into it.)

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