Why do C++ streams use char instead of unsigned char?

Question

I\'ve always wondered why the C++ Standard library has instantiated basic_[io]stream and all its variants using the char type instead of the unsigned char

Answer 1

I think this comment explains it well. To quote:

signed char and unsigned char are arithmetic, integral types just like int and unsigned int. On the other hand, char is expressly intended to be the "I/O" type that represents some opaque, system-specific fundamental unit of data on your platform. I would use them in this spirit.