Is there any character that is never used (in ASCII or Unicode)
c++
Solution
All ASCII code points are used for characters, but there are plenty of Unicode code points that are guaranteed to not be characters, for example U+FFFF.
I'm not sure of what you would do with this information, though. While the code point is not a valid character you can construct strings that include it. Those strings would not be legal in Unicode, but you seem to imply that you can store any data, not just Unicode text.
Problem
I just need one character that I can set in character arrays indicating that a particular location or a series of locations are free and available for storing data. I need this because I am making a simple memory pool and need to reset freed blocks and indicate them as free. Any help would be appreciated.