cpp/regex/regex iterator/regex iterator

Constructs a new :

@1@ Default constructor. Constructs an end-of-sequence iterator.

@2@ Constructs a from the sequence of characters, the regular expression , and a flag  that governs matching behavior. This constructor performs an initial call to std with this data. If the result of this initial call is, is set to an end-of-sequence iterator.

@3@ Copies a.

@4@ The overload is not allowed to be called with a temporary regex, since the returned iterator would be immediately invalidated.