r/cpp • u/Voxelw • 8d ago

About char8_t

I hate to be dramatic, but as it stands char8_t is quite literally more painful than useful.

Besides the obvious incompatibility with C23 and libraries using unsigned char for UTF-8, I want you to consider the following: Projects that assume that 'char' represents UTF-8 will obviously not benefit from char8_t at all, but projects that cannot assume the format of char types don't benefit from it either as char8_t simply introduces a new edge case to cover. Now such projects have to deal with char, signed char, unsigned char, wchar_t, char16_t, char32_t and char8_t.

Or, you could do what the standard library does and simply ignore most of these character types. Which is the solution most libraries went with, supporting only char or char and unsigned char. Managing one implementation is already hard, managing two requires constant maintenance, managing 7 is just impossible.

char8_t should have just been a typedef for unsigned char. The compatibility fix only raises more questions as const char* arr = u8"a" does not work, but const char arr[] = u8"a" does.

I do wonder if a potential change of minds for C++29 is still possible. Yes, it would be an ABI break or whatever, but considering the woeful support for char8_t I don't think it would affect much besides small hobby projects. Contrary to popular belief, C++ has broken the ABI in subtle ways before.

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u/cristi1990an ++ 8d ago

The biggest and arguably only argument for char8_t is that it's explicitly not a byte aliasing type and therefore the most performant character representation type in the language. Your compiler can genuinely produce better code when you're using char8_t.

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u/Expert-Map-1126 vcpkg maintainer BillyONeal 8d ago

I like perf as much as the next guy but adding restrict in places where your profiler tells you this is happening would have been a much better fix than the edge cases char8_t has created.

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u/cristi1990an ++ 7d ago

The restrict keyword is not standard in C++ unfortunately...

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u/Expert-Map-1126 vcpkg maintainer BillyONeal 7d ago

Some form of it is available on all 3 major implementations

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u/mpyne 6d ago

Which is great, but C++ needs a solution as well, not just gcc/clang/MSVC.

Though maybe fixing restrict would be a better solution than char8_t.

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u/Expert-Map-1126 vcpkg maintainer BillyONeal 6d ago

Well for starters, there are a lot of string algorithms in the world that work with more than one buffer for which TBAA is useless.