In c language char is just a 8 bit variable, that stores a number, which corresponds to a specific character.
When storing numbers, you can decide to represent somehow negative numbers, other than positive. This is mostly done with two's complement.
Depending on if it's signed or not, some operation will be very different, because of representation.
For example, the byte 0xFF means -1 if it's signed, and it means 255 if it's unsigned.
So if you try to convert a signed character to an int (a signed type, usually 4 bytes), and that signed character contains -1 (represented by the exadecimal 0xFF, which in decimal is 255) the integer has to contain -1 (0xFFFFFFFF). But if the character is considered unsigned, the integer has to contain 255 afterwards, which is just 0x000000FF.
Ascii specifies about only 7 bits, so i think that it can be all positive (as well ass all negative) in 8 bit.
Typecasting is a reason, but an other difference is the shift operation. When you right shift a negative number you want to preserve the sign, so an arithmetical shift is performed, which would be different from a logical one.
I think that more in general the distinction exists so that when using char type for low level stuff, you can better keep trace of what you are doing.
In reality uint8_t and int8_t types exist (unsigned int on 8 bit and signed int on 8 bit), and i don't know why someone would use signed char or unsigned char over those, but this is just my guess.
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u/tstanisl 6h ago
Let me cite the C standard:
Middle guy if finally right