c++ - `filesystem` with c++17 doesn't work on my mac os x high sierra

Question

I'm following this tutorial:

http://www.bfilipek.com/2017/08/cpp17-details-filesystem.html

to checkout new c++ filesystem feature. However I'm unable to compile even minimal example on my machine:

#include <string>
#include <iostream>
#include <filesystem>

namespace fs = std::filesystem;

int main()
{
    std::string path = "/";

    for (auto & p : fs::directory_iterator(path))
        std::cout << p << std::endl;
}

I was using XCode, CLion and command line while trying to compile it but nothing works, I have Version 9.3 (9E145) with (seemingly proper) project settings, none of which work:

Here is my CMakeLists.txt file for CLion:

cmake_minimum_required(VERSION 3.8)

project(FileSystem2)

set(CMAKE_CXX_STANDARD 17)

add_executable(FileSystem2 main.cpp)

Here is an output from > gxx --version:

Nevertheless this is what I get as an output from my IDEs:

What am I doing wrong, it looks to me that my compiler should support c++17?

---

Edit

As per Owen Morgan's answer I've installed clang (actual install command was brew install llvm) but it now complains about absence of string.h. Any thoughts?

Answer 1

The compiler shipped with Xcode supports C++17 language features but not C++17 standard library features. Looking at your screenshot you will see the standard library support goes up to C++11, and Apple has not yet shipped a version of clang that has stdlib support for either C++14 or C++17.

However hope is not lost! You can download the newest version of clang from the brew package manager.

brew install clang

Then you can compile by setting your cmake compiler flags to be your custom brew version and then running that.

Here is a link how to do that: http://antonmenshov.com/2017/09/09/clang-openmp-setup-in-xcode/

Edit:

After installing llvm you will need to link your llvm path into your current shell. I have a shell script that I use at work to get this set up properly. Hope this helps.

#!/bin/bash
brew update
brew install --with-toolchain llvm # llvm but with all the headers
xcode-select --install # installs additional headers that you might be mimssing.
echo 'export PATH="/usr/local/opt/llvm/bin:$PATH"' >> ~/.bash_profile # exports the custom llvm path into the shell 
sudo ln -s /usr/local/opt/llvm/bin/clang++ /usr/local/bin/clang++-brew # optional but I like to have a symlink set.

Edit 2:

Clang 6.0 doesn't have <filesystem> included on macOS yet, however you can get <experimental/filesystem>, and link against -lc++experimental, and use std::experimental::filesystem instead of std::filesystem.

Final command line invocation:

Owen$ /usr/local/Cellar/llvm/6.0.0/bin/clang++ fs.cpp -std=c++1z -L /usr/local/Cellar/llvm/6.0.0/lib/ -lc++experimental

Edit 3:

Current clang version 7.0.1 supports either <filesystem> or <experimental/filesystem>. In any case, the compiler command line must be slightly different:

Owen$ /usr/local/Cellar/llvm/7.0.1/bin/clang++ main.cpp -std=c++1z -L /usr/local/Cellar/llvm/7.0.1/lib/ -lc++fs

with -lc++fs instead of -lc++experimental. Optionally, you can replace-std=c++1z with -std=c++17 as well.