1 files changed, 9 insertions, 3 deletions

diff --git a/diff.cpp b/diff.cpp
index ea9b04e..85d3167 100644
--- a/diff.cpp
+++ b/diff.cpp
@@ -21,9 +21,10 @@ std::string Diff::apply(const std::string& old_version) const
 {
  std::string result{old_version};
 
- result.erase(m_pos0, m_pos1 - m_pos0);
-
- result.insert(m_pos0, m_data);
+ if (m_pos0 <= m_pos1 && m_pos1 <= old_version.size()) {
+  result.erase(m_pos0, m_pos1 - m_pos0);
+  result.insert(m_pos0, m_data);
+ }
  
  return result;
 }
@@ -143,6 +144,11 @@ void Diff::create(const std::string& xml)
  create(ptree);
 }
 
+bool Diff::empty() const
+{
+ return m_pos0 == m_pos1 && m_data.empty();
+}
+
 boost::property_tree::ptree Diff::get_structure() const
 {
  pt::ptree ptree;