Why are type keywords ended with "_t" suffix?

Question

I understand that size_t has _t suffix since its alias/typedef. However I can't understand for what reason char16_t, char32_t and wchar_t contains _t suffix.

Answer 1

For wchar_t:

In C++, wchar_t is a distinct fundamental type (and thus it is not defined in <cwchar> nor any other header).

In C, this is a typedef of an integral type.

For char16_t and char32_t, defined in <cuchar>/uchar.c:

In C, this header defines two macros: char16_t and char32_t, which map to unsigned integral types of the appropriate size (the same as uint_least16_t and uint_least32_t, respectively).

In C++, char16_t and char32_t are fundamental types (and thus this header does not define such macros in C++).

So, in both cases, even though they are fundamental types in C++, they keep the _t for compatibility with C, where they were typedefs or macros.