What is the C++17 equivalent to boost::filesystem::unique_path()?

Question

std::filesystem on C++17, and std::experimental::filesystem for many pre-C++17 compilers, are based on boost::filesystem and almost all of it is obvious to port to the newer std.

But I see no std::filesystem equivalent to boost::filesystem::unique_path().

Is there an equivalent in std that I'm not noticing? Or is there a recommended approach I should take to mimic the implementation?

I'm really hoping to replace the boost::filesystem dependency when my code notices it's compiling on a platform that supports std::filesystem, and unique_path() is the only not obvious part of my conversion.

Answer 1

unique_path was removed because it was a potential attack vector for malware. There is a window of opportunity between calling unique_path and opening a file at that location during which some other process could create the same file. Depending on what the user does with the file, this may or may not constitute a security vulnerability. A similar issue exists with the POSIX function tmpnam.

As noted in this discussion, this issue will be dealt with in the next iteration of the Filesystem library. Until then, you can either continue using Boost.Filesystem, use the std::tmpnam function provided in <cstdio>, or use safer platform-specific alternatives like mkstemp.

Answer 2

As far as I can tell there is really no exact equivalent in C++17.

You didn't really specify what exactly you want to do but if you just need to store a temporary file somewhere then you should be able to mimic a similar functionality with std::filesystem::temp_directory_path which you can append with a randomly generated filename (which you can do like this, or modify it accordingly if you require the exact same naming format as boost::filesystem::unique_path())

Or if you just need to store any temporary file, you can use std::tmpfile.