setComment() will assert if comment does not start with / (or if it were NULL, which would have seg-faulted before).

src/lib_json/json_value.cpp

@@ -1,3 +1,4 @@
+#include <iostream>
 #include <json/value.h>
 #include <json/writer.h>
 #include <utility>
@@ -149,6 +150,9 @@ Value::CommentInfo::setComment( const char *text )
 {
    if ( comment_ )
       valueAllocator()->releaseStringValue( comment_ );
+   JSON_ASSERT( text );
+   JSON_ASSERT_MESSAGE( text[0]==NULL || text[0]=='/', "Comments must start with /");
+   // It seems that /**/ style comments are acceptable as well.
    comment_ = valueAllocator()->duplicateStringValue( text );
 }