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?

You cannot print dir_entry into std::cout, you probably meant dir_entry.path() or dir_entry.path().string(). — user1143634
– user1143634, Commented Jun 20, 2022 at 12:02
Indeed. Looks like your implementation doesn't implement operator<< for directory_entry. — user1143634
– user1143634, Commented Jun 20, 2022 at 12:04
Which version of Clang are you using? Are you using libc++ or libstdc++? — user17732522
– user17732522, Commented Jun 20, 2022 at 12:05
There was LWG issue 3171. The error makes sense if you are using a standard library version that doesn't implement the resolution yet but does implement the resolution to LWG 2989. — user17732522
– user17732522, Commented Jun 20, 2022 at 12:08
@HappyMachine -- minor point: cppreference is a very good site, but it is not in any sense "official". — Pete Becker
– Pete Becker, Commented Jun 20, 2022 at 12:16

Yksisarvinen · Accepted Answer · 2022-06-20 12:19:08Z

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

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