Add missing include file for step-69

diff --git a/examples/step-69/step-69.cc b/examples/step-69/step-69.cc
index b4f1b00c9bcf0258dab61f577edadfe6c7908d80..49062a7540d30a00c79a42527b26e6f506df36dc 100644 (file)
--- a/examples/step-69/step-69.cc
+++ b/examples/step-69/step-69.cc
@@ -82,8 +82,9 @@
 #include <boost/range/irange.hpp>
 #include <boost/range/iterator_range.hpp>
 
-// For std::isnan and std::isinf.
+// For std::isnan, std::isinf, and std::ifstream
 #include <cmath>
+#include <fstream>
 
 // @sect3{Class template declarations}
 //