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Is there any tools for detecting files and lines that is using c++17 features?

August 1, 2022

Question

Background

I’m developing some software with c++17.
Recentlty a customer requested us to list files and lines that is using c++17 features.
The reason is that they have to applicate deviation permits for using c++17 feature because their internal coding conventions is standarized by c++14.

It may be possible to detect them using a compiler, but the compiler stops every time it detects an error, making it time-consuming to detect all errors.

For ease to list up, I asked above question!

What we tried

I tried to use cpplint/clang-format.
But these tools didn’t detect c++17 feature despite c++14 option. The code I tested is below.

#include <iostream>

// C++17 feature
namespace aaa::bbb::ccc
{
  void f()
  { std::cout << "a new nested namespace definition is worked!\n"; }
}

namespace aaa
{
  namespace bbb
  {
    namespace ccc
    {
      void g()
      { std::cout << "a legacy nested namespace definition is workded.\n"; }
    }
  }
}

int main()
{
  aaa::bbb::ccc::f();
  aaa::bbb::ccc::g();
}

Thank you!

>Solution :

If you compile with Clang, the -Wpre-c++17-compat diagnostic flag warns about the case from your example:

<source>:4:14: warning: nested namespace definition is incompatible with C++ standards before C++17 [-Wpre-c++17-compat]
namespace aaa::bbb::ccc
             ^
1 warning generated.

It will also warn on if/switch initialization statements, pack fold expressions, decomposition declarations and a bunch of other common C++17 features that aren’t in earlier versions.

The full list of cases is included in the reference of all diagnostic flags, here:

https://clang.llvm.org/docs/DiagnosticsReference.html#wpre-c-17-compat

By default, Clang will warn, then carry on compiling. If your build uses -Werror, you may want to disable that for this warning with -Wno-error=pre-c++17-compat.