c++ – Is there such a thing as non-utf8 character

c++ – Is there such a thing as non-utf8 character

Yes. 0xC0, 0xC1, 0xF5, 0xF6, 0xF7, 0xF8, 0xF9, 0xFA, 0xFB, 0xFC, 0xFD, 0xFE, 0xFF are invalid UTF-8 code units. A UTF-8 code unit is 8 bits. If by char you mean an 8-bit byte, then the invalid UTF-8 code units would be char values that do not appear in UTF-8 encoded text.

std::string only knows about raw char values, it knows nothing about particular character encodings that use char to hold encoded values.

Many common UTF-8 implementations use char to hold encoded codeunits (though C++20 will introduce char8_t and std::u8string for this purpose instead). But other character encodings (Windows-12##, ISO-8859-#, etc) can also fit their encoded values in char elements, too.

Any char value that falls within the ASCII range (0x00 .. 0x7F) will fit in 1 char and map to the same codepoint value in Unicode (U+0000 .. U+007F), but any char value in the ANSI range but not in the ASCII range (0x80 .. 0xFF) is subject to interpretation by whatever character encoding created the char values. Some encodings use 1 char per character, some use multiple chars.

So yes, there is such a thing as a non-UTF-8 char.

c++ – Is there such a thing as non-utf8 character

You can check out the UTF-8 standard on Wiki. Not every sequence of bytes is a valid UTF-8 character. Even if its a single byte: 0x11111000, 0x11111111 are not valid first bytes in UTF-8.

Though, I doubt that it is a good idea to use a non-UTF-8 character as a delimiter. You might find certain program (like Notepad++) having issues with reading output of your strings.