Preserve const-ness in string comparer.

diff --git a/retrace.hpp b/retrace.hpp
index 806d6ed..b697adb 100644 (file)
--- a/retrace.hpp
+++ b/retrace.hpp
@@ -97,7 +97,7 @@ struct Entry {
 
 
 struct stringComparer {
-  bool operator() (const char *a, const  char *b) {
+  bool operator() (const char *a, const  char *b) const {
     return strcmp(a, b) < 0;
   }
 };