Using clang-tidy to check c++17 code - c++

Question

I installed clang-tidy on Ubuntu using:
sudo apt install clang-tidy
I ran it on a simple C++ 17 file, and got a warning and errors:
/home/erelsgl/Dropbox/ariel/CPLUSPLUS/intro/01-single-file/ptr.cpp:17:3: warning: 'auto' type specifier is a C++11 extension [clang-diagnostic-c++11-extensions]
auto i = make_unique<int>();
^
/home/erelsgl/Dropbox/ariel/CPLUSPLUS/intro/01-single-file/ptr.cpp:17:12: error: use of undeclared identifier 'make_unique' [clang-diagnostic-error]
auto i = make_unique<int>();
How can I tell clang-tidy to check this file according to c++17 standards?
NOTE: To build the program, I run:
clang++-5.0 --std=c++17 ptr.cpp

Answer 1

Depending on your compiler / clang-tidy version, the default C++ standard version used to compile source files may vary. clang's default std version is gnu++-98 (or gnu++-14 starting with clang 6.0), and typically clang-tidy has the same defaults as clang.
I'm guessing that -std=c++17 (or -std=c++1z) isn't specified in the C++ compiler flags, used for compiling ptr.cpp, so clang-tidy falls back to the default -std=gnu++98, and therefore gives warnings for C++11 code.
For asking clang-tidy to handle C++17, you should specify the -std flag as suggested by #n.m., as parameter to the -extra-arg option, for example:
clang-tidy -p . ptr.cpp -extra-arg=-std=c++17
Edit:
Since clang++-5.0 is used for compiling ptr.cpp, it may be a good idea to use the matching clang-tidy version, 5.0 (on Ubuntu 16.04, the default clang-tidy version installed through apt is 3.8), that is:
clang-tidy-5.0 -p . ptr.cpp -extra-arg=-std=c++17
If not already installed, you could grab it from:
https://www.ubuntuupdates.org/package/xorg-edgers/xenial/main/base/clang-tidy-5.0