How do I enable C++17 in Xcode for Mac OSX? - c++

Question

How do I enable C++17 in Xcode (9.4.1) on OSX High Sierra (10.13.5)?

Answer 1

Steps to use C++17 in Xcode (9.4.1) on OSX High Sierra (10.13.5):
Open existing or create a new C++ project in Xcode
Click on the "show project navigator" button. It is located on the top-left section of Xcode window just below the minimize/maximize/close window buttons. It is the left-most icon and looks like a folder.
Click on "Build Settings" and scroll down to find and expand the section "Apple LLVM 9.0 - Language - C++"
Change the C++ Language Dialect combobox selection to "C++17 [-std=c++17]"
Verification steps:
Now when I output __cplusplus, I see 201703, and I am able to compile C++17 features, such as if constexpr.
template<class T>
int compute(T x) {
if constexpr( supportsAPI(T{}) ) {
// only gets compiled if the condition is true
return x.Method();
} else {
return 0;
}
}
int main(){
cout << __cplusplus << endl;
return 0;
}
Output:
201703
Program ended with exit code: 0

Answer 2

When using development CocoaPods (writing a C++ library) I had also to update podspec of this library containing c++ 17 code to make compile host application which included this pod.
So I added these flags to library's podspec
spec.xcconfig = {
"CLANG_CXX_LANGUAGE_STANDARD" => "c++17",
"CLANG_CXX_LIBRARY" => "libc++"
}