Added operator- member implementation and improved test cases

* operator- takes a reference to a const std::string::const_iterator and as such enables determining the actual position of a codepoint within a string
* ranged for loops in test cases now take the iterator value by rvalue reference instead of by value

1 files changed, 2 insertions, 0 deletions

diff --git a/src/codepoint_iterator.h b/src/codepoint_iterator.h
index b505587..d1806e5 100644
--- a/src/codepoint_iterator.h
+++ b/src/codepoint_iterator.h
@@ -22,6 +22,8 @@ class CodepointIterator : public std::iterator<std::bidirectional_iterator_tag,
 		bool operator!=(const CodepointIterator&) const;
 		bool operator!=(const std::string::const_iterator&) const;
 
+		std::ptrdiff_t operator-(const std::string::const_iterator&) const;
+
 		char32_t operator*();
 
 		CodepointIterator& operator++();