Some refactorings:

- Overrides added
 - usages of push_back() replaced with emplace_back()
 - Loop variable made const-refernce
 - NULL replaced with nullptr
 - Names used in the declaration and definition unified
 - size() replaced with empty
 - Identical cases merged

examples/210-Evt-EventListeners.cpp

@@ -30,7 +30,7 @@ std::ostream& operator<<(std::ostream& out, Catch::Tag t) {
 template< typename T >
 std::ostream& operator<<( std::ostream& os, std::vector<T> const& v ) {
     os << "{ ";
-    for ( auto x : v )
+    for ( const auto& x : v )
         os << x << ", ";
     return os << "}";
 }
@@ -63,7 +63,7 @@ void print( std::ostream& os, int const level, Catch::MessageInfo const& info )
 
 void print( std::ostream& os, int const level, std::string const& title, std::vector<Catch::MessageInfo> const& v ) {
     os << ws(level  ) << title << ":\n";
-    for ( auto x : v )
+    for ( const auto& x : v )
     {
         os << ws(level+1) << "{\n";
         print( os, level+2, x );

examples/231-Cfg-OutputStreams.cpp

@@ -18,7 +18,7 @@ class out_buff : public std::stringbuf {
 public:
     out_buff(std::FILE* stream):m_stream(stream) {}
     ~out_buff();
-    int sync() {
+    int sync() override {
         int ret = 0;
         for (unsigned char c : str()) {
             if (putc(c, m_stream) == EOF) {