Fix unused field warning in clang.

Change-Id: I71d590a1e5b2709f0e2dcf97faaebda5cb918fc7
Tested: on Linux.

src/idl_gen_cpp.cpp

@@ -1621,6 +1621,11 @@ class CppGenerator : public BaseGenerator {
         NumToString((*id)++) + "__;";
   }
 
+  static void PaddingDeclaration(int bits, std::string *code_ptr, int *id) {
+    (void)bits;
+    *code_ptr += "(void)padding" + NumToString((*id)++) + "__;";
+  }
+
   static void PaddingInitializer(int bits, std::string *code_ptr, int *id) {
     (void)bits;
     *code_ptr += ",\n        padding" + NumToString((*id)++) + "__(0)";
@@ -1702,10 +1707,20 @@ class CppGenerator : public BaseGenerator {
       }
     }
 
+    padding_id = 0;
+    std::string padding_list;
+    for (auto it = struct_def.fields.vec.begin();
+         it != struct_def.fields.vec.end(); ++it) {
+      auto field = *it;
+      GenPadding(*field, &padding_list, &padding_id, PaddingDeclaration);
+    }
+
     code_.SetValue("ARG_LIST", arg_list);
     code_.SetValue("INIT_LIST", init_list);
+    code_.SetValue("PADDING_LIST", padding_list);
     code_ += "  {{STRUCT_NAME}}({{ARG_LIST}})";
     code_ += "      : {{INIT_LIST}} {";
+    if (padding_list.length()) code_ += "    {{PADDING_LIST}}";
     code_ += "  }";
 
     // Generate accessor methods of the form:

tests/monster_test_generated.h

@@ -154,6 +154,7 @@ MANUALLY_ALIGNED_STRUCT(2) Test FLATBUFFERS_FINAL_CLASS {
       : a_(flatbuffers::EndianScalar(_a)),
         b_(flatbuffers::EndianScalar(_b)),
         padding0__(0) {
+    (void)padding0__;
   }
   int16_t a() const {
     return flatbuffers::EndianScalar(a_);
@@ -199,6 +200,7 @@ MANUALLY_ALIGNED_STRUCT(16) Vec3 FLATBUFFERS_FINAL_CLASS {
         padding1__(0),
         test3_(_test3),
         padding2__(0) {
+    (void)padding0__;(void)padding1__;(void)padding2__;
   }
   float x() const {
     return flatbuffers::EndianScalar(x_);