Scieneer Common Lisp 1.3.9 online documentation

file-string-length stream object[Generic Function]

Return the delta in the stream file-position that would be caused by writing the object to the stream, or return nil if this can not be determined. The position of character file streams is defined as the number of characters read back so if an output conversion occurs that affects the number of characters read back then the file-string-length will differ from the object string length. A default method is provided for character output streams that returns nil.