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@xxxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxxxx> > > School of Aerospace Science and Technology, Xidian University -- Xi Ruoyao <ryxi@xxxxxxxxxxxxxxxxx> School of Aerospace Science and Technology, Xidian University