difference between length() and size() in c++ code example

Example: what is difffrence between s.length() and s.size()

The size() function is consistent with other STL containers 
(like vector, map, etc.) and length() is consistent with most 
peoples intuitive notion of character strings like a word, sentence
or paragraph. We say a paragraph'ss length not its size, so length() 
is to make things more readable.