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). 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
