From: Maciej W. Rozycki > Sent: 03 March 2022 11:31 .. > It does, but, oh dear, it's a "solution" to a problem we have created in > the first place. Why do we ever want to have signed characters in the TTY > layer, and then to vary between platforms? It's asking for portability > issues. C 'char' is signed because the pdp/11 byte load sign extended. I guess some ABI use unsigned char to avoid issues with all the functions that take/return an int parameter that is either a 'char' cast to 'unsigned char' or EOF. EOF is usually (-1) - but doesn't have to be. But it needs to be different from any value obtained by casting a 'char' to 'unsigned char'. (But that may only need to be all characters, not all values of 'char'.) Then you get the requirement that: sizeof (int) >= sizeof (short) >= sizeof (char) which means that it is perfectly valid for all 3 to be the same size [1]. In that case 'unsigned char' promotes to 'unsigned int' which probably breaks some code. It also makes defining EOF troublesome! [1] The C compiler for a DSP had this 'feature'. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
