2 files changed, 7 insertions, 4 deletions

diff --git a/cpp/nissy.cpp b/cpp/nissy.cpp
index e3193e1..6e1b700 100644
--- a/cpp/nissy.cpp
+++ b/cpp/nissy.cpp
@@ -166,11 +166,13 @@ namespace nissy {
                 ifs.read(reinterpret_cast<char *>(data.data()), size);
         }
 
-        error solver::check_data() const
+        error solver::check_data()
         {
-                auto err = nissy_checkdata(data.size(),
+                auto err_value = nissy_checkdata(data.size(),
                     reinterpret_cast<const char *>(data.data()));
-                return error{err};
+                error err{err_value};
+                data_checked = err.ok();
+                return err;
         }
 
         void solver::unload_data()
diff --git a/cpp/nissy.h b/cpp/nissy.h
index 7ab466d..448704e 100644
--- a/cpp/nissy.h
+++ b/cpp/nissy.h
@@ -84,10 +84,11 @@ namespace nissy {
                 size_t size;
                 std::string id;
                 std::vector<std::byte> data;
+                bool data_checked;
 
                 error generate_data();
                 void read_data(std::ifstream&);
-                error check_data() const;
+                error check_data();
                 void unload_data();
                 solve_result solve(const cube&, nissflag, unsigned minmoves,
                     unsigned maxmoves, unsigned maxsols, int optimal,