Does an empty string contain an empty string in C++?

Question

Just had an interesting argument in the comment to one of my questions. My opponent claims that the statement \"\" does not contain \"\"<

Answer 1

It's easy. String A contains sub-string B if there is an argument offset such that A.substr(offset, B.size()) == B. No special cases for empty strings needed.

So, let's see. std::string("").substr(0,0) turns out to be std::string(""). And we can even check your "counter-example". std::string("").substr(0,0).substr(0,0) is also well-defined and empty. Turtles all the way down.