UTF-8 symbol written to the terminal output - c++

Question

I've been trying to understand the working principle of the operator<< of std::cout in C++. I've found that it prints UTF-8 symbols, for instance:
The simple program is:
#include <iostream>
unsigned char t[] = "ي";
unsigned char m0 = t[0];
unsigned char m1 = t[1];
int main()
{
std::cout << t << std::endl; // Prints ي
std::cout << (int)t[0] << std::endl; // Prints 217
std::cout << (int)t[1] << std::endl; // Prints 138
std::cout << m0 << std::endl; // Prints �
std::cout << m1 << std::endl; // Prints �
}
DEMO
How does the terminal that produces output determine that it must interpret t as a single symbol ي, but not as two symbols � �?

Answer 1

You are dealing with two different types, unsigned char[] and unsigned char.
If you were to do sizeof on t, you'd find that it occupied
three bytes, and strlen( t ) will return 2. On the other
hand, m0 and m1 are single characters.
When you output a unsigned char[], it is converted to an
unsigned char*, and the stream outputs all of the bytes until
it encounters a '\0' (which is the third byte in t). When
you output an unsigned char, the stream outputs just that
byte. So in your first line, the output device receives
2 bytes, and then the end of line. In the last two, it receives
1 byte, and then the end of line. And that byte, followed by
the end of line, is not a legal UTF-8 character, so the display
device displays something to indicate that there was an error,
or that it did not understand.
When working with UTF-8 (or any other multibyte encoding), you
cannot extract single bytes from a string and expect them to
have any real meaning.

Answer 2

The terminal is determining how to display the bytes you are feeding it. You are feeding it a newline (std::endl) between the two bytes of the 2-byte UTF-8-encoded Unicode character. Instead of this:
std::cout << m0 << std::endl; // Prints �
std::cout << m1 << std::endl; // Prints �
Try this:
std::cout << m0 << m1 << std::endl; // Prints ي
Why do m0 and m1 print as � in your original code?
Because your code is sending the bytes [217, 110, 138, 110], which is not interpretable as UTF-8. (Assuming std::endl corresponds to the \n character, value 110.)