When I create a default QMake-based template "Plain C++ Application" with the GCC-based Kit, I see that any of STL includes are not found in editor... they are marked as "no such file or directory". And any of std functions and classes are not highlighted at pressing of CTRL+mouse click. BUT, the project compiles without any errors.

UPD: ClangCodeModel plugin is disabled.

UPD2: When I enable the ClangCodeModel plugin, it says similar: "file not found" (I mean about, e.g. iostream file)

UPD3:

[denis@archlinux ~]$ `gcc -print-prog-name=cc1plus` -v
несуществующий каталог "/usr/lib/gcc/x86_64-pc-linux-gnu/6.2.1/../../../../x86_64-pc-linux-gnu/include" проигнорирован
порядок поиска для #include "...":
порядок поиска для #include <...>:
/usr/lib/gcc/x86_64-pc-linux-gnu/6.2.1/../../../../include/c++/6.2.1
/usr/lib/gcc/x86_64-pc-linux-gnu/6.2.1/../../../../include/c++/6.2.1/x86_64-pc-linux-gnu
/usr/lib/gcc/x86_64-pc-linux-gnu/6.2.1/../../../../include/c++/6.2.1/backward
/usr/lib/gcc/x86_64-pc-linux-gnu/6.2.1/include
/usr/local/include
/usr/lib/gcc/x86_64-pc-linux-gnu/6.2.1/include-fixed
/usr/include
Конец списка поиска.

UPD4:

[denis@archlinux ~]$ ls /usr/lib/gcc/x86_64-pc-linux-gnu/6.2.1/../../../../include/c++/6.2.1/ | grep iostream
iostream
[denis@archlinux ~]$