For sparse enums, use a switch statement to generate EnumNameXXX(). (#4845)

src/idl_gen_cpp.cpp

@@ -981,6 +981,23 @@ class CppGenerator : public BaseGenerator {
       code_ += ";";
 
       code_ += "  return EnumNames{{ENUM_NAME}}()[index];";
+      code_ += "}";
+      code_ += "";
+    } else {
+      code_ += "inline const char *EnumName{{ENUM_NAME}}({{ENUM_NAME}} e) {";
+
+      code_ += "  switch (e) {";
+
+      for (auto it = enum_def.vals.vec.begin(); it != enum_def.vals.vec.end();
+           ++it) {
+        const auto &ev = **it;
+        code_ += "    case {{ENUM_NAME}}_" + Name(ev) + ": return \"" +
+                 Name(ev) + "\";";
+      }
+
+      code_ += "    default: return \"\";";
+      code_ += "  }";
+
       code_ += "}";
       code_ += "";
     }