Fixed CreateVectorOfStructs for native_type (2nd try) (#4276)

* Added support for serializing native_type with CreateVectorOfNativeStructs

* Added support for serializing native_type with CreateVectorOfSortedNativeStructs

* Added C++ code generation for vectors of native_types

include/flatbuffers/flatbuffers.h

@@ -1197,6 +1197,24 @@ FLATBUFFERS_FINAL_CLASS
     return Offset<Vector<const T *>>(EndVector(len));
   }
 
+  /// @brief Serialize an array of native structs into a FlatBuffer `vector`.
+  /// @tparam T The data type of the struct array elements.
+  /// @tparam S The data type of the native struct array elements.
+  /// @param[in] v A pointer to the array of type `S` to serialize into the
+  /// buffer as a `vector`.
+  /// @param[in] len The number of elements to serialize.
+  /// @return Returns a typed `Offset` into the serialized data indicating
+  /// where the vector is stored.
+  template<typename T, typename S> Offset<Vector<const T *>> CreateVectorOfNativeStructs(
+      const S *v, size_t len) {
+    extern T Pack(const S&);
+    typedef T (*Pack_t)(const S&);
+    std::vector<T> vv(len);
+    std::transform(v, v+len, vv.begin(), *(Pack_t)&Pack);
+    return CreateVectorOfStructs<T>(vv.data(), vv.size());
+  }
+
+
   #ifndef FLATBUFFERS_CPP98_STL
   /// @brief Serialize an array of structs into a FlatBuffer `vector`.
   /// @tparam T The data type of the struct array elements.
@@ -1229,6 +1247,19 @@ FLATBUFFERS_FINAL_CLASS
     return CreateVectorOfStructs(data(v), v.size());
   }
 
+  /// @brief Serialize a `std::vector` of native structs into a FlatBuffer `vector`.
+  /// @tparam T The data type of the `std::vector` struct elements.
+  /// @tparam S The data type of the `std::vector` native struct elements.
+  /// @param[in]] v A const reference to the `std::vector` of structs to
+  /// serialize into the buffer as a `vector`.
+  /// @return Returns a typed `Offset` into the serialized data indicating
+  /// where the vector is stored.
+  template<typename T, typename S> Offset<Vector<const T *>> CreateVectorOfNativeStructs(
+      const std::vector<S> &v) {
+    return CreateVectorOfNativeStructs<T, S>(data(v), v.size());
+  }
+
+
   /// @cond FLATBUFFERS_INTERNAL
   template<typename T>
   struct StructKeyComparator {
@@ -1253,6 +1284,19 @@ FLATBUFFERS_FINAL_CLASS
     return CreateVectorOfSortedStructs(data(*v), v->size());
   }
 
+  /// @brief Serialize a `std::vector` of native structs into a FlatBuffer `vector`
+  /// in sorted order.
+  /// @tparam T The data type of the `std::vector` struct elements.
+  /// @tparam S The data type of the `std::vector` native struct elements.
+  /// @param[in]] v A const reference to the `std::vector` of structs to
+  /// serialize into the buffer as a `vector`.
+  /// @return Returns a typed `Offset` into the serialized data indicating
+  /// where the vector is stored.
+  template<typename T, typename S> Offset<Vector<const T *>> CreateVectorOfSortedNativeStructs(
+      std::vector<S> *v) {
+    return CreateVectorOfSortedNativeStructs<T, S>(data(*v), v->size());
+  }
+
   /// @brief Serialize an array of structs into a FlatBuffer `vector` in sorted
   /// order.
   /// @tparam T The data type of the struct array elements.
@@ -1267,6 +1311,24 @@ FLATBUFFERS_FINAL_CLASS
     return CreateVectorOfStructs(v, len);
   }
 
+  /// @brief Serialize an array of native structs into a FlatBuffer `vector` in sorted
+  /// order.
+  /// @tparam T The data type of the struct array elements.
+  /// @tparam S The data type of the native struct array elements.
+  /// @param[in] v A pointer to the array of type `S` to serialize into the
+  /// buffer as a `vector`.
+  /// @param[in] len The number of elements to serialize.
+  /// @return Returns a typed `Offset` into the serialized data indicating
+  /// where the vector is stored.
+  template<typename T, typename S> Offset<Vector<const T *>> CreateVectorOfSortedNativeStructs(
+      S *v, size_t len) {
+    extern T Pack(const S&);
+    typedef T (*Pack_t)(const S&);
+    std::vector<T> vv(len);
+    std::transform(v, v+len, vv.begin(), *(Pack_t)&Pack);
+    return CreateVectorOfSortedStructs<T>(vv, len);
+  }
+
   /// @cond FLATBUFFERS_INTERNAL
   template<typename T>
   struct TableKeyComparator {

src/idl_gen_cpp.cpp

@@ -1753,7 +1753,15 @@ class CppGenerator : public BaseGenerator {
           }
           case BASE_TYPE_STRUCT: {
             if (IsStruct(vector_type)) {
-              code += "_fbb.CreateVectorOfStructs(" + value + ")";
+              auto native_type =
+                field.value.type.struct_def->attributes.Lookup("native_type");
+              if (native_type) {
+                code += "_fbb.CreateVectorOfNativeStructs<";
+                code += WrapInNameSpace(*vector_type.struct_def) + ">";
+              } else {
+                code += "_fbb.CreateVectorOfStructs";              	
+              }
+              code += "(" + value + ")";
             } else {
               code += "_fbb.CreateVector<flatbuffers::Offset<";
               code += WrapInNameSpace(*vector_type.struct_def) + ">>";