read-char

(read-char &optional stream eof-error-p eof-value recursive-p)

Reads one character from stream (default: standard input) and returns it. The stream may be a file stream opened by open/with-open-file, a string input stream from with-input-from-string, or a TCP or TLS socket handle -- on a socket the character is assembled from the wire's UTF-8 bytes, so read-char and read-byte can be mixed on one connection. At end of input it signals an end-of-file condition unless eof-error-p is nil, in which case it returns eof-value (default nil). Because the condition is the registered end-of-file class, the usual CL lexer shape -- a read loop wrapped in (handler-case ... (end-of-file (e) ...)) -- terminates as written. A character is one Unicode code point on every backend, decoded from the stream's UTF-8. Malformed input reads as the JVM's decoder reads it, on every backend: a byte that starts no sequence is one U+FFFD (the replacement character), and so is a sequence that a wrong byte or the end of the input cuts short -- the wrong byte then starts the next character, so the bytes 41 E9 42 read as A, U+FFFD, B. read-line, peek-char and read-sequence decode the same way. recursive-p is accepted and ignored: it only matters to a reader macro's recursive read.