3939. §[format.string.std] char is not formatted as a character when charT is wchar_t

Section: [format.string.std] Status: New Submitter: S. B. Tam Opened: 2023-05-26 Last modified: 2023-06-01 14:06:54 UTC

Priority: 3

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(See discussion at microsoft/STL/pull/3723) [format.string.std] p21 says:

The available integer presentation types for integral types other than bool and charT are specified in Table 68.

When charT is wchar_t, the ordinary character type char falls into this category, and thus a char gets formatted as an integer by default, not as a character.

This arguably doesn't affect the std::format family, because they are specified in terms of make_format_args, which calls the basic_format_arg constructor, which converts char to wchar_t ( [format.arg] (6.2)). But it does affect the std::formatter<char, wchar_t> specialization, which isn't specified to use basic_format_arg.

This is especially problematic after P2286R8, which makes std::formatter<char, wchar_t> debug-enabled, but there's no debug format for integral types other than charT.

Perhaps [format.string.std] should say that the formatting arguments are converted as if through the basic_format_arg constructor.

At the time of writing, on libstdc++ and libc++, std::formatter<char, wchar_t> formats the argument as a character when no specifier is given (godbolt.org/z/nnsEcvna3), while MSVC STL's std::formatter<char, wchar_t> outputs the integer value. But I'm about to change MSVC STL to match the other implementations.

[2023-06-01; Reflector poll]

Set priority to 3 after reflector poll.

Proposed resolution: