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Re: Questions on the result of dependency generation
On 2017-08-19 02:05 -0700, chran wang wrote:
> Hello Ruoyao,
>
> For (B), I'm sorry that I forgot to say that I changed '#include
> "c/c.h" ' to '#include "c.h" ' in that case. For others, I did not
> encounter any errors on my machine as you showed.
>
> I'm using ubuntu 16.04. At first, I tried with g++ 5.4.0 since it is
> shipped with ubuntu. Then I compiled a gcc 7.1 from its source code. I
> got the same result under g++ 7.1 (and no error output).
>
For (A) there should be error output.
Try g++ -E -v c/c.cpp in root. Then you can see which file "c/c.h" really
is.
Note that you may have a "c/c.h" in system header directories (-isystem).
-MM doesn't mention system headers. By default your include directive can
not find your root/c/c.h. So maybe you have "-isystem root" or likewise,
or maybe "/usr/include/c/c.h" (weird name collision).
Check you environment CPLUS_INCLUDE_PATH since it may add system header
directories unintentionally.
>
> On Sat, Aug 19, 2017 at 1:32 AM, Xi Ruoyao <ryxi@stu.xidian.edu.cn> wrote:
> > On 2017-08-18 15:52 -0700, chran wang wrote:
> > > Hello,
> > >
> > > I observed some weird results about the dependency generation.
> > >
> > > Suppose the source code structure is as follows:
> > >
> > > root
> > > |-- c
> > > | |-- c.cpp
> > > | |-- c.h
> > >
> > > 'c.cpp' includes the header file 'c.h' by
> > > #include "c/c.h"
> > >
> > > Now I try to generate the dependencies for c/c.cpp.
> > >
> > > (A) If I'm now in 'root' folder and run command
> > > g++ -MM -MT c/c.o c/c.cpp
> > > the compiler outputs
> > > c/c.o : c/c.cpp # which is wrong because it lacks c/c.h
> >
> > Your #include directive is bad. The compiler gives:
> >
> > LANG= g++ -MM -MT c/c.o c/c.cpp
> > c/c.cpp:1:10: fatal error: c/c.h: No such file or directory
> > #include "c/c.h"
> > ^~~~~~~
> > compilation terminated.
> >
> > > (B) If I'm in folder 'c' and run command
> > > g++ -MM -MT c.o c.cpp
> > > the compiler can ouput the correct results
> > > c.o : c.cpp c.h
> >
> > Ditto.
> >
> > > (C) If I'm in the parent folder of folder 'root' and run command
> > > g++ -I./root -MM -MT root/c/c.o root/c/c.cpp
> > > the results is also correct:
> > > root/c/c,o : root/c/c.cpp root/c/c.h
> >
> > With -I./root the include directive is correct.
> >
> > > (D) Now, if I'm in folder 'root' again and include the head file 'c.h'
> > > for 'c.cpp' by
> > > #include "c.h" instead of #include "c/c.h"
> > > the result is also correct.
> >
> > Ditto.
> >
> > > I'm wondering why (A) cannot give a correct dependency output but (B),
> > > (C) and (D) can.
> >
> > Which version of GCC are you using? It seems like a preprocessor bug
> > and I can't reproduce it with GCC 4.6, 4.7, 5.x, 6.x and 7.x.
> > --
> > Xi Ruoyao <ryxi@stu.xidian.edu.cn>
> > School of Aerospace Science and Technology, Xidian University
--
Xi Ruoyao <ryxi@stu.xidian.edu.cn>
School of Aerospace Science and Technology, Xidian University