2849. Why does !is_regular_file(from) cause copy_file to report a "file already exists" error?

Section: 31.12.13.5 [fs.op.copy.file] Status: C++20 Submitter: Tim Song Opened: 2016-12-17 Last modified: 2021-06-06

Priority: 2

View all other issues in [fs.op.copy.file].

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Discussion:

[fs.op.copy_file]/4 says that copy_file reports "a file already exists error as specified in [fs.err.report] if" any of several error conditions exist.

It's not clear how some of those error conditions, such as !is_regular_file(from), can be sensibly described as "file already exists". Pretty much everywhere else in the filesystem specification just says "an error" without further elaboration.

[2017-01-27 Telecon]

Priority 2; Jonathan to provide updated wording.

[2018-01-16, Jonathan comments]

I said I'd provide updated wording because I wanted to preserve the requirement that the reported error is "file already exists" for some of the error cases. I no longer think that's necessary, so I think the current P/R is fine. Please note that I don't think new wording is needed.

[ 2018-01-23 Moved to Tentatively Ready after 6 positive votes on c++std-lib. ]

[2018-3-17 Adopted in Jacksonville]

Proposed resolution:

This wording is relative to N4713.

  1. Edit [fs.op.copy_file]/4 as indicated:

    bool copy_file(const path& from, const path& to, copy_options options);
bool copy_file(const path& from, const path& to, copy_options options,
               error_code& ec) noexcept;

    -4- Effects: As follows:

    1. (4.1) — Report a file already existsan error as specified in 31.12.5 [fs.err.report] if:

      1. (4.1.1) —[…]

    3. (4.2) —[…]