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1b1ed1a
(Get the code!)
I was just bitten by this. I tried to upgrade from clang-3.4 to clang-3.5, and was unable to compile anything because the standard headers were not found. I then downgraded back to clang-3.4, and was surprised to find that to be broken as well. Since at that point I was stuck, I plowed on until I found a solution.
The issue seems related to the fact that gcc-4.9 exists at this point in time, but g++-4.9 does not. I think this means it only affects those who have partially upgraded to gcc-4.9 (the C compiler, but not the C++ compiler). Clang is searching for the standard C++ header in directories that don't exist and not finding them. There also seem to be issues where Clang is searching only for /usr/include/c++ without adding an appropriate version number.
One fix is to add symlinks until Clang can find the files it's looking for.
The currently searched header directories can be found with:
clang++ -E -x c++ - -v < /dev/null
Assuming a test file 'file.cpp' that includes a failing header, you can see where g++ is successfully finding a header (and Clang is failing) like this:
strace -f g++ file.cpp -std=gnu++11 -o file.o 2>&1 | grep header
strace -f clang++ file.cpp -std=gnu++11 -o file.o 2>&1 | grep header
There are several ways of helping Clang to find the headers it is looking for, all of varying degree of likelihood to break other things. I decided the path of least harm was to create symlinks like this:
$ ls -l /usr/include/c++/
lrwxrwxrwx 1 root root 3 Dec 20 15:50 backward -> 4.8
lrwxrwxrwx 1 root root 37 Dec 20 15:56 x86_64-linux-gnu -> /usr/include/
Once you solve the issue of finding header files, you then won't be able to find libstdc++.so. I fixed that with this:
sudo ln -s /usr/lib/
Now that I've done this, both clang-3.4 and clang-3.5 will work, although not simultaneously because Ubuntu supports multiple versions of GCC but not of Clang. Note that this is just an ugly workaround for a bug that should be fixed by Ubuntu. Once this is fixed, these steps will be unnecessary, and possibly hazardous. Personally, I think that Ubuntu should support having multiple versions of Clang installed, and rather than deinstalling one version to install another.