std::filesystem example not compiling on c++ 17

Question

I cant compile this official cpp filesystem reference example using c++ 17 clang:

https://en.cppreference.com/w/cpp/filesystem/recursive_directory_iterator

#include <fstream>
#include <iostream>
#include <filesystem>
namespace fs = std::filesystem;

int main()
{
   fs::current_path(fs::temp_directory_path());
   fs::create_directories("sandbox/a/b");
   std::ofstream("sandbox/file1.txt");
   fs::create_symlink("a", "sandbox/syma");

   // Iterate over the `std::filesystem::directory_entry` elements explicitly
   for (const fs::directory_entry& dir_entry : 
       fs::recursive_directory_iterator("sandbox"))
   {
       std::cout << dir_entry << '\n';
   }
   std::cout << "-----------------------------\n";
   // Iterate over the `std::filesystem::directory_entry` elements using `auto`
   for (auto const& dir_entry : fs::recursive_directory_iterator("sandbox"))
   {
       std::cout << dir_entry << '\n';
   }

   fs::remove_all("sandbox");
}

The compiler is returning:

/main.cpp:17:19: error: invalid operands to binary expression ('std::__1::ostream' (aka 'basic_ostream') and 'const fs::directory_entry') std::cout << dir_entry << std::endl;

Can anyone help?

Answer 1

There was a defect in C++17 standard that didn't allow operator<< to be called with std::filesystem::directory_entry , reported in LWG 3171 . It's now fixed as defect report, but it seems clang only fixed it in version 14: https://godbolt.org/z/3arTcGYvY . gcc seems to have backported the fix to all versions that support std::filesystem (that is, gcc9.1 and up): https://godbolt.org/z/fh7cdMxso