diff --git a/tensorflow/lite/toco/tflite/export.cc b/tensorflow/lite/toco/tflite/export.cc
index d72a902001d..d109ab875b5 100644
--- a/tensorflow/lite/toco/tflite/export.cc
+++ b/tensorflow/lite/toco/tflite/export.cc
@@ -52,7 +52,7 @@ using ::tflite::Tensor;
 namespace {
 
 // Check if a TensorFlow Op is a control flow op by its name.
-bool IsControlFlowOp(const string& tensorflow_op) {
+bool IsControlFlowOp(const std::string& tensorflow_op) {
   // Technically this is equivalent to `::tensorflow::Node::IsControlFlow()`.
   // It requires to construct a `::tensorflow::Graph` to use that helper
   // function, so we simply hardcode the list of control flow ops here.
@@ -68,7 +68,7 @@ bool IsControlFlowOp(const string& tensorflow_op) {
 }
 
 // Check if a TensorFlow Op is unsupported by the Flex runtime.
-bool IsUnsupportedFlexOp(const string& tensorflow_op) {
+bool IsUnsupportedFlexOp(const std::string& tensorflow_op) {
   if (IsControlFlowOp(tensorflow_op)) {
     return true;
   }
@@ -82,14 +82,14 @@ bool IsUnsupportedFlexOp(const string& tensorflow_op) {
 }
 
 // Map from operator name to TF Lite enum value, for all builtins.
-const std::map<string, BuiltinOperator>& GetBuiltinOpsMap() {
-  static std::map<string, BuiltinOperator>* builtin_ops = nullptr;
+const std::map<std::string, BuiltinOperator>& GetBuiltinOpsMap() {
+  static std::map<std::string, BuiltinOperator>* builtin_ops = nullptr;
   if (builtin_ops == nullptr) {
-    builtin_ops = new std::map<string, BuiltinOperator>();
+    builtin_ops = new std::map<std::string, BuiltinOperator>();
 
     for (int i = BuiltinOperator_MIN; i <= BuiltinOperator_MAX; ++i) {
       BuiltinOperator op = static_cast<BuiltinOperator>(i);
-      string name = EnumNameBuiltinOperator(op);
+      std::string name = EnumNameBuiltinOperator(op);
       if (op != BuiltinOperator_CUSTOM && !name.empty()) {
         (*builtin_ops)[name] = op;
       }
@@ -99,10 +99,10 @@ const std::map<string, BuiltinOperator>& GetBuiltinOpsMap() {
 }
 
 void WriteModelToString(const flatbuffers::FlatBufferBuilder& builder,
-                        string* file_contents) {
+                        std::string* file_contents) {
   const uint8_t* buffer = builder.GetBufferPointer();
   int size = builder.GetSize();
-  *file_contents = string(reinterpret_cast<const char*>(buffer), size);
+  *file_contents = std::string(reinterpret_cast<const char*>(buffer), size);
 }
 
 }  // Anonymous namespace.
@@ -115,7 +115,7 @@ OperatorKey::OperatorKey(
     bool enable_select_tf_ops) {
   // Get the op name (by Toco definition).
   const ::toco::Operator& op = *op_signature.op;
-  string name = HelpfulOperatorTypeName(op);
+  std::string name = HelpfulOperatorTypeName(op);
 
   bool is_builtin = false;
   const auto& builtin_ops = GetBuiltinOpsMap();
@@ -146,7 +146,7 @@ OperatorKey::OperatorKey(
       is_flex_op_ = true;
       flex_tensorflow_op_ = tensorflow_op;
       custom_code_ =
-          string(::tflite::kFlexCustomCodePrefix) + flex_tensorflow_op_;
+          std::string(::tflite::kFlexCustomCodePrefix) + flex_tensorflow_op_;
     } else {
       custom_code_ = tensorflow_op;
     }
@@ -158,7 +158,7 @@ OperatorKey::OperatorKey(
     is_flex_op_ = true;
     flex_tensorflow_op_ = name;
     custom_code_ =
-        string(::tflite::kFlexCustomCodePrefix) + flex_tensorflow_op_;
+        std::string(::tflite::kFlexCustomCodePrefix) + flex_tensorflow_op_;
   } else {
     // If Flex is disabled or the original TensorFlow NodeDef isn't available,
     // we produce a custom op. This gives developers a chance to implement
@@ -175,7 +175,7 @@ OperatorKey::OperatorKey(
 
 void LoadTensorsMap(const Model& model, TensorsMap* tensors_map) {
   // First find a list of unique array names.
-  std::set<string> names;
+  std::set<std::string> names;
   for (const auto& array_pair : model.GetArrayMap()) {
     names.insert(array_pair.first);
   }
@@ -218,7 +218,7 @@ Offset<Vector<Offset<Tensor>>> ExportTensors(
   std::map<int, Offset<Tensor>> ordered_tensors;
 
   for (const auto& array_pair : model.GetArrayMap()) {
-    const string& tensor_name = array_pair.first;
+    const std::string& tensor_name = array_pair.first;
     const toco::Array& array = *array_pair.second;
 
     int buffer_index = buffers_to_write->size();
@@ -283,7 +283,7 @@ Offset<Vector<int32_t>> ExportOutputTensors(
     const Model& model, const details::TensorsMap& tensors_map,
     FlatBufferBuilder* builder) {
   std::vector<int32_t> outputs;
-  for (const string& output : model.flags.output_arrays()) {
+  for (const std::string& output : model.flags.output_arrays()) {
     outputs.push_back(tensors_map.at(output));
   }
   return builder->CreateVector<int32_t>(outputs);
@@ -295,10 +295,10 @@ Offset<Vector<Offset<OperatorCode>>> ExportOperatorCodes(
     const details::OperatorsMap& operators_map, FlatBufferBuilder* builder,
     const ExportParams& params) {
   // Map from operator name to TF Lite enum value, for all builtins.
-  std::map<string, BuiltinOperator> builtin_ops;
+  std::map<std::string, BuiltinOperator> builtin_ops;
   for (int i = BuiltinOperator_MIN; i <= BuiltinOperator_MAX; ++i) {
     BuiltinOperator op = static_cast<BuiltinOperator>(i);
-    string name = EnumNameBuiltinOperator(op);
+    std::string name = EnumNameBuiltinOperator(op);
     if (op != BuiltinOperator_CUSTOM && !name.empty()) {
       builtin_ops[name] = op;
     }
@@ -349,13 +349,13 @@ Offset<Vector<Offset<Operator>>> ExportOperators(
   std::vector<Offset<Operator>> op_vector;
   for (const auto& op : model.operators) {
     std::vector<int32_t> inputs;
-    for (const string& input : op->inputs) {
+    for (const std::string& input : op->inputs) {
       // -1 is the ID for optional tensor in TFLite output
       int id = model.IsOptionalArray(input) ? -1 : tensors_map.at(input);
       inputs.push_back(id);
     }
     std::vector<int32_t> outputs;
-    for (const string& output : op->outputs) {
+    for (const std::string& output : op->outputs) {
       outputs.push_back(tensors_map.at(output));
     }
     const toco::OperatorSignature op_signature = {op.get(), &model};
@@ -428,15 +428,15 @@ Offset<Vector<Offset<Buffer>>> ExportBuffers(
   return builder->CreateVector(buffer_vector);
 }
 
-tensorflow::Status Export(const Model& model, string* output_file_contents,
+tensorflow::Status Export(const Model& model, std::string* output_file_contents,
                           const ExportParams& params) {
   const auto ops_by_type = BuildOperatorByTypeMap(params.enable_select_tf_ops);
   return Export(model, output_file_contents, params, ops_by_type);
 }
 
-void ParseControlFlowErrors(std::set<string>* custom_ops,
-                            std::vector<string>* error_msgs) {
-  std::set<string> unsupported_control_flow_ops;
+void ParseControlFlowErrors(std::set<std::string>* custom_ops,
+                            std::vector<std::string>* error_msgs) {
+  std::set<std::string> unsupported_control_flow_ops;
   // Check if unsupported ops contains control flow ops. It's impossible
   // to implement these ops as custom ops at the moment.
   for (const auto& op : *custom_ops) {
@@ -471,10 +471,10 @@ void ExportModelVersionBuffer(
 }
 
 tensorflow::Status Export(
-    const Model& model, string* output_file_contents,
+    const Model& model, std::string* output_file_contents,
     const ExportParams& params,
     const std::map<OperatorType, std::unique_ptr<BaseOperator>>& ops_by_type) {
-  for (const string& input_array : model.GetInvalidInputArrays()) {
+  for (const std::string& input_array : model.GetInvalidInputArrays()) {
     if (model.HasArray(input_array)) {
       return tensorflow::errors::InvalidArgument(
           absl::StrCat("Placeholder ", input_array,
@@ -509,11 +509,11 @@ tensorflow::Status Export(
   }
 
   // The set of used builtin ops.
-  std::set<string> builtin_ops;
+  std::set<std::string> builtin_ops;
   // The set of custom ops (not including Flex ops).
-  std::set<string> custom_ops;
+  std::set<std::string> custom_ops;
   // The set of Flex ops which are not supported.
-  std::set<string> unsupported_flex_ops;
+  std::set<std::string> unsupported_flex_ops;
 
   for (const auto& it : operators_map) {
     const details::OperatorKey& key = it.first;
@@ -540,7 +540,7 @@ tensorflow::Status Export(
                "40-tflite-op-request.md\n and pasting the following:\n\n";
       };
 
-      std::vector<string> error_msgs;
+      std::vector<std::string> error_msgs;
       ParseControlFlowErrors(&custom_ops, &error_msgs);
 
       // Remove ExpandDims and ReorderAxes from unimplemented list unless they
@@ -549,7 +549,7 @@ tensorflow::Status Export(
       // transformation is unable to run because the output shape is not
       // defined. This causes unnecessary confusion during model conversion
       // time.
-      std::set<string> custom_ops_final;
+      std::set<std::string> custom_ops_final;
       for (const auto& op_type : custom_ops) {
         if (op_type != "ReorderAxes" && op_type != "ExpandDims") {
           custom_ops_final.insert(op_type);
diff --git a/tensorflow/lite/toco/tflite/export.h b/tensorflow/lite/toco/tflite/export.h
index 3af77ffcf43..64f7c7b128f 100644
--- a/tensorflow/lite/toco/tflite/export.h
+++ b/tensorflow/lite/toco/tflite/export.h
@@ -35,19 +35,19 @@ struct ExportParams {
 
 // Transform the given tf.mini model into a TF Lite flatbuffer and deposit the
 // result in the given string.
-tensorflow::Status Export(const Model& model, string* output_file_contents,
+tensorflow::Status Export(const Model& model, std::string* output_file_contents,
                           const ExportParams& params);
 
 // Export API with custom TFLite operator mapping.
 tensorflow::Status Export(
-    const Model& model, string* output_file_contents,
+    const Model& model, std::string* output_file_contents,
     const ExportParams& params,
     const std::map<OperatorType, std::unique_ptr<BaseOperator>>& ops_by_type);
 
 // This is for backward-compatibility.
 // TODO(ycling): Remove the deprecated entry functions.
 inline void Export(const Model& model, bool allow_custom_ops,
-                   bool quantize_weights, string* output_file_contents) {
+                   bool quantize_weights, std::string* output_file_contents) {
   ExportParams params;
   params.allow_custom_ops = allow_custom_ops;
   params.quantize_weights =
@@ -60,7 +60,7 @@ inline void Export(const Model& model, bool allow_custom_ops,
 // TODO(ycling): Remove the deprecated entry functions.
 inline void Export(
     const Model& model, bool allow_custom_ops, bool quantize_weights,
-    string* output_file_contents,
+    std::string* output_file_contents,
     const std::map<OperatorType, std::unique_ptr<BaseOperator>>& ops_by_type) {
   ExportParams params;
   params.allow_custom_ops = allow_custom_ops;
@@ -72,7 +72,7 @@ inline void Export(
 
 // This is for backward-compatibility.
 // TODO(ycling): Remove the deprecated entry functions.
-inline void Export(const Model& model, string* output_file_contents) {
+inline void Export(const Model& model, std::string* output_file_contents) {
   ExportParams params;
   params.allow_custom_ops = true;
   auto status = Export(model, output_file_contents, params);
@@ -82,7 +82,7 @@ inline void Export(const Model& model, string* output_file_contents) {
 namespace details {
 
 // A map from tensor name to its final position in the TF Lite buffer.
-using TensorsMap = std::unordered_map<string, int>;
+using TensorsMap = std::unordered_map<std::string, int>;
 
 // A key to identify an operator.
 // Only when `type` is `kUnsupported`, `custom_code` is filled to
diff --git a/tensorflow/lite/toco/tflite/export_test.cc b/tensorflow/lite/toco/tflite/export_test.cc
index 19b77543c66..ed347a28d51 100644
--- a/tensorflow/lite/toco/tflite/export_test.cc
+++ b/tensorflow/lite/toco/tflite/export_test.cc
@@ -34,13 +34,13 @@ using ::testing::HasSubstr;
 class ExportTest : public ::testing::Test {
  protected:
   void ResetOperators() { input_model_.operators.clear(); }
-  void AddTensorsByName(std::initializer_list<string> names) {
-    for (const string& name : names) {
+  void AddTensorsByName(std::initializer_list<std::string> names) {
+    for (const std::string& name : names) {
       input_model_.GetOrCreateArray(name);
     }
   }
-  void AddOperatorsByName(std::initializer_list<string> names) {
-    for (const string& name : names) {
+  void AddOperatorsByName(std::initializer_list<std::string> names) {
+    for (const std::string& name : names) {
       if (name == "Conv") {
         auto* op = new ConvOperator;
         op->padding.type = PaddingType::kSame;
@@ -153,14 +153,15 @@ class ExportTest : public ::testing::Test {
   }
 
   tensorflow::Status ExportAndReturnStatus(const ExportParams& params) {
-    string result;
+    std::string result;
     return Export(input_model_, &result, params);
   }
 
-  std::vector<string> ExportAndSummarizeOperators(const ExportParams& params) {
-    std::vector<string> names;
+  std::vector<std::string> ExportAndSummarizeOperators(
+      const ExportParams& params) {
+    std::vector<std::string> names;
 
-    string result;
+    std::string result;
     auto status = Export(input_model_, &result, params);
     if (!status.ok()) {
       LOG(INFO) << status.error_message();
@@ -171,10 +172,12 @@ class ExportTest : public ::testing::Test {
 
     for (const ::tflite::OperatorCode* opcode : *model->operator_codes()) {
       if (opcode->builtin_code() != ::tflite::BuiltinOperator_CUSTOM) {
-        names.push_back(string("builtin:") + ::tflite::EnumNameBuiltinOperator(
-                                                 opcode->builtin_code()));
+        names.push_back(
+            std::string("builtin:") +
+            ::tflite::EnumNameBuiltinOperator(opcode->builtin_code()));
       } else {
-        names.push_back(string("custom:") + opcode->custom_code()->c_str());
+        names.push_back(std::string("custom:") +
+                        opcode->custom_code()->c_str());
       }
     }
 
@@ -185,7 +188,7 @@ class ExportTest : public ::testing::Test {
       const ExportParams& params) {
     std::vector<uint32_t> indices;
 
-    string result;
+    std::string result;
     if (!Export(input_model_, &result, params).ok()) return indices;
     auto* model = ::tflite::GetModel(result.data());
 
@@ -257,7 +260,7 @@ TEST_F(ExportTest, ExportMinRuntime) {
   params.enable_select_tf_ops = false;
   params.quantize_weights = QuantizedBufferType::NONE;
 
-  string output;
+  std::string output;
   auto status = Export(input_model_, &output, params);
   auto* model = ::tflite::GetModel(output.data());
   EXPECT_EQ(model->metadata()->size(), 1);
@@ -265,7 +268,8 @@ TEST_F(ExportTest, ExportMinRuntime) {
   auto buf = model->metadata()->Get(0)->buffer();
   auto* buffer = (*model->buffers())[buf];
   auto* array = buffer->data();
-  string version(reinterpret_cast<const char*>(array->data()), array->size());
+  std::string version(reinterpret_cast<const char*>(array->data()),
+                      array->size());
   EXPECT_EQ(version, "1.6.0");
 }
 
@@ -275,7 +279,7 @@ TEST_F(ExportTest, ExportEmptyMinRuntime) {
   ExportParams params;
   params.allow_custom_ops = true;
 
-  string output;
+  std::string output;
   auto status = Export(input_model_, &output, params);
   auto* model = ::tflite::GetModel(output.data());
   EXPECT_EQ(model->metadata()->size(), 1);
@@ -283,7 +287,8 @@ TEST_F(ExportTest, ExportEmptyMinRuntime) {
   auto buf = model->metadata()->Get(0)->buffer();
   auto* buffer = (*model->buffers())[buf];
   auto* array = buffer->data();
-  string version(reinterpret_cast<const char*>(array->data()), array->size());
+  std::string version(reinterpret_cast<const char*>(array->data()),
+                      array->size());
   EXPECT_EQ(version, "");
 }
 
@@ -296,7 +301,7 @@ TEST_F(ExportTest, UnsupportedControlFlowErrors) {
   // The model contains control flow ops which are not convertible, so we should
   // check the returned error message.
 
-  string output;
+  std::string output;
   const auto ops_by_type = BuildOperatorByTypeMap();
   auto status = Export(input_model_, &output, params, ops_by_type);
   EXPECT_EQ(status.error_message(),
@@ -318,7 +323,7 @@ TEST_F(ExportTest, UnsupportedOpsAndNeedEnableFlex) {
   params.allow_custom_ops = false;
   params.enable_select_tf_ops = false;
 
-  string output;
+  std::string output;
   const auto ops_by_type = BuildOperatorByTypeMap();
   auto status = Export(input_model_, &output, params, ops_by_type);
   EXPECT_EQ(
@@ -348,7 +353,7 @@ TEST_F(ExportTest, UnsupportedOpsNeedCustomImplementation) {
   params.allow_custom_ops = false;
   params.enable_select_tf_ops = true;
 
-  string output;
+  std::string output;
   const auto ops_by_type = BuildOperatorByTypeMap();
   auto status = Export(input_model_, &output, params, ops_by_type);
   EXPECT_EQ(
@@ -378,7 +383,7 @@ TEST_F(ExportTest, UnsupportedControlFlowAndCustomOpsErrors) {
   // The model contains control flow ops which are not convertible, so we should
   // check the returned error message.
 
-  string output;
+  std::string output;
   const auto ops_by_type = BuildOperatorByTypeMap();
   auto status = Export(input_model_, &output, params, ops_by_type);
   EXPECT_EQ(
@@ -407,11 +412,11 @@ TEST_F(ExportTest, UnsupportedControlFlowAndCustomOpsErrors) {
 TEST_F(ExportTest, QuantizeWeights) {
   // Sanity check for quantize_weights parameter.
   BuildQuantizableTestModel();
-  string unquantized_result;
+  std::string unquantized_result;
   Export(input_model_, true, /*quantize_weights*/ false, &unquantized_result);
 
   BuildQuantizableTestModel();
-  string quantized_result;
+  std::string quantized_result;
   Export(input_model_, true, /*quantize_weights*/ true, &quantized_result);
 
   // The quantized models should be smaller.
@@ -443,12 +448,13 @@ class OpSetsTest : public ExportTest {
     }
   }
 
-  std::vector<string> ImportExport(std::initializer_list<string> op_names) {
+  std::vector<std::string> ImportExport(
+      std::initializer_list<std::string> op_names) {
     ResetOperators();
     if (!import_all_ops_as_unsupported_) {
       AddOperatorsByName(op_names);
     } else {
-      for (const string& name : op_names) {
+      for (const std::string& name : op_names) {
         auto* op = new TensorFlowUnsupportedOperator;
         op->tensorflow_op = name;
         input_model_.operators.emplace_back(op);
@@ -644,7 +650,7 @@ TEST_F(VersionedOpExportTest, Export) {
   AddConvOp(false);
   AddConvOp(true);
 
-  string result;
+  std::string result;
   const auto ops_by_type = BuildFakeOperatorByTypeMap();
   Export(input_model_, true, false, &result, ops_by_type);
 
diff --git a/tensorflow/lite/toco/tflite/import.cc b/tensorflow/lite/toco/tflite/import.cc
index 0f3dd48652e..136aa4ffaa8 100644
--- a/tensorflow/lite/toco/tflite/import.cc
+++ b/tensorflow/lite/toco/tflite/import.cc
@@ -99,7 +99,7 @@ void ImportTensors(const ::tflite::Model& input_model, Model* model) {
 
 void ImportOperators(
     const ::tflite::Model& input_model,
-    const std::map<string, std::unique_ptr<BaseOperator>>& ops_by_name,
+    const std::map<std::string, std::unique_ptr<BaseOperator>>& ops_by_name,
     const details::TensorsTable& tensors_table,
     const details::OperatorsTable& operators_table, Model* model) {
   // TODO(aselle): add support for multiple subgraphs.
@@ -112,12 +112,12 @@ void ImportOperators(
       LOG(FATAL) << "Index " << index << " must be between zero and "
                  << operators_table.size();
     }
-    string opname = operators_table.at(index);
+    std::string opname = operators_table.at(index);
 
     // Find and use the appropriate operator deserialization factory.
     std::unique_ptr<Operator> new_op = nullptr;
     if (ops_by_name.count(opname) == 0) {
-      string effective_opname = "TENSORFLOW_UNSUPPORTED";
+      std::string effective_opname = "TENSORFLOW_UNSUPPORTED";
       if (ops_by_name.count(effective_opname) == 0) {
         LOG(FATAL) << "Internal logic error: TENSORFLOW_UNSUPPORTED not found.";
       }
@@ -147,10 +147,10 @@ void ImportOperators(
       auto input_index = inputs->Get(i);
       // input_index == -1 indicates optional tensor.
       if (input_index != -1) {
-        const string& input_name = tensors_table.at(input_index);
+        const std::string& input_name = tensors_table.at(input_index);
         op->inputs.push_back(input_name);
       } else {
-        const string& tensor_name =
+        const std::string& tensor_name =
             toco::AvailableArrayName(*model, "OptionalTensor");
         model->CreateOptionalArray(tensor_name);
         op->inputs.push_back(tensor_name);
@@ -159,7 +159,7 @@ void ImportOperators(
     auto outputs = input_op->outputs();
     for (int i = 0; i < outputs->Length(); i++) {
       auto output_index = outputs->Get(i);
-      const string& output_name = tensors_table.at(output_index);
+      const std::string& output_name = tensors_table.at(output_index);
       op->outputs.push_back(output_name);
     }
   }
@@ -173,7 +173,7 @@ void ImportIOTensors(const ModelFlags& model_flags,
     auto inputs = (*input_model.subgraphs())[0]->inputs();
     if (inputs) {
       for (int input : *inputs) {
-        const string& input_name = tensors_table.at(input);
+        const std::string& input_name = tensors_table.at(input);
         model->flags.add_input_arrays()->set_name(input_name);
       }
     }
@@ -184,7 +184,7 @@ void ImportIOTensors(const ModelFlags& model_flags,
     auto outputs = (*input_model.subgraphs())[0]->outputs();
     if (outputs) {
       for (int output : *outputs) {
-        const string& output_name = tensors_table.at(output);
+        const std::string& output_name = tensors_table.at(output);
         model->flags.add_output_arrays(output_name);
       }
     }
@@ -199,7 +199,7 @@ bool Verify(const void* buf, size_t len) {
 }  // namespace
 
 std::unique_ptr<Model> Import(const ModelFlags& model_flags,
-                              const string& input_file_contents) {
+                              const std::string& input_file_contents) {
   ::tflite::AlwaysTrueResolver r;
   if (!::tflite::Verify(input_file_contents.data(), input_file_contents.size(),
                         r, ::tflite::DefaultErrorReporter())) {
diff --git a/tensorflow/lite/toco/tflite/import.h b/tensorflow/lite/toco/tflite/import.h
index f5de3b53b5b..bac55aae8b9 100644
--- a/tensorflow/lite/toco/tflite/import.h
+++ b/tensorflow/lite/toco/tflite/import.h
@@ -24,17 +24,17 @@ namespace tflite {
 
 // Parse the given string as TF Lite flatbuffer and return a new tf.mini model.
 std::unique_ptr<Model> Import(const ModelFlags &model_flags,
-                              const string &input_file_contents);
+                              const std::string &input_file_contents);
 
 namespace details {
 
 // The names of all tensors found in a TF Lite model.
-using TensorsTable = std::vector<string>;
+using TensorsTable = std::vector<std::string>;
 
 // The names of all operators found in TF Lite model. If the operator is
 // builtin, the string representation of the corresponding enum value is used
 // as name.
-using OperatorsTable = std::vector<string>;
+using OperatorsTable = std::vector<std::string>;
 
 void LoadTensorsTable(const ::tflite::Model &input_model,
                       TensorsTable *tensors_table);
diff --git a/tensorflow/lite/toco/tflite/import_test.cc b/tensorflow/lite/toco/tflite/import_test.cc
index b00c4124d83..6163ebab45b 100644
--- a/tensorflow/lite/toco/tflite/import_test.cc
+++ b/tensorflow/lite/toco/tflite/import_test.cc
@@ -134,9 +134,9 @@ class ImportTest : public ::testing::Test {
 
     input_model_ = ::tflite::GetModel(builder_.GetBufferPointer());
   }
-  string InputModelAsString() {
-    return string(reinterpret_cast<char*>(builder_.GetBufferPointer()),
-                  builder_.GetSize());
+  std::string InputModelAsString() {
+    return std::string(reinterpret_cast<char*>(builder_.GetBufferPointer()),
+                       builder_.GetSize());
   }
   flatbuffers::FlatBufferBuilder builder_;
   const ::tflite::Model* input_model_ = nullptr;
diff --git a/tensorflow/lite/toco/tflite/op_version.cc b/tensorflow/lite/toco/tflite/op_version.cc
index cf127a9f459..efa53c69cae 100644
--- a/tensorflow/lite/toco/tflite/op_version.cc
+++ b/tensorflow/lite/toco/tflite/op_version.cc
@@ -29,7 +29,7 @@ namespace tflite {
 
 // Deprecated and please register new ops/versions in
 // tflite/tools/versioning/op_version.cc".
-string GetMinimumRuntimeVersionForModel(const Model& model) {
+std::string GetMinimumRuntimeVersionForModel(const Model& model) {
   // Use this as the placeholder string if a particular op is not yet included
   // in any Tensorflow's RC/Final release source package. Once that op is
   // included in the release, please update this with the real version string.
@@ -37,8 +37,8 @@ string GetMinimumRuntimeVersionForModel(const Model& model) {
   // A map from the version key of an op to its minimum runtime version.
   // For example, {{kAveragePool, 1}, "1.5.0"},  means the 1st version of
   // AveragePool requires a minimum TF Lite runtime version '1.5.0`.
-  static const std::map<std::pair<OperatorType, int>, string>* op_version_map =
-      new std::map<std::pair<OperatorType, int>, string>({
+  static const std::map<std::pair<OperatorType, int>, std::string>*
+      op_version_map = new std::map<std::pair<OperatorType, int>, std::string>({
           {{OperatorType::kAveragePool, 1}, "1.5.0"},
           {{OperatorType::kAveragePool, 2}, "1.14.0"},
           {{OperatorType::kAveragePool, 3}, kPendingReleaseOpVersion},
@@ -253,7 +253,7 @@ string GetMinimumRuntimeVersionForModel(const Model& model) {
       tflite::BuildOperatorByTypeMap(false /*enable_select_tf_ops=*/);
   OperatorSignature op_signature;
   op_signature.model = &model;
-  string model_min_version;
+  std::string model_min_version;
   for (const auto& op : model.operators) {
     if (op_types_map.find(op->type) == op_types_map.end()) continue;
     op_signature.op = op.get();
diff --git a/tensorflow/lite/toco/tflite/op_version_test.cc b/tensorflow/lite/toco/tflite/op_version_test.cc
index 14b086471b7..8466fc35ad7 100644
--- a/tensorflow/lite/toco/tflite/op_version_test.cc
+++ b/tensorflow/lite/toco/tflite/op_version_test.cc
@@ -27,9 +27,9 @@ TEST(OpVersionTest, MinimumVersionForSameOpVersions) {
   Model model;
   // Float convolutional kernel is introduced since '1.5.0'.
   std::unique_ptr<ConvOperator> conv(new ConvOperator());
-  const string conv_input = "conv_input";
-  const string conv_filter = "conv_filter";
-  const string conv_output = "conv_output";
+  const std::string conv_input = "conv_input";
+  const std::string conv_filter = "conv_filter";
+  const std::string conv_output = "conv_output";
   conv->inputs.push_back(conv_input);
   conv->inputs.push_back(conv_filter);
   conv->outputs.push_back(conv_output);
@@ -44,8 +44,8 @@ TEST(OpVersionTest, MinimumVersionForSameOpVersions) {
 
   // Float softmax kernel is introduced since '1.5.0'.
   std::unique_ptr<SoftmaxOperator> softmax(new SoftmaxOperator());
-  const string softmax_input = "softmax_input";
-  const string softmax_output = "softmax_output";
+  const std::string softmax_input = "softmax_input";
+  const std::string softmax_output = "softmax_output";
   softmax->inputs.push_back(softmax_input);
   softmax->outputs.push_back(softmax_output);
   array_map[softmax_input] = std::unique_ptr<Array>(new Array);
@@ -60,9 +60,9 @@ TEST(OpVersionTest, MinimumVersionForMultipleOpVersions) {
   Model model;
   // Dilated DepthWiseConvolution is introduced since '1.12.0'.
   std::unique_ptr<DepthwiseConvOperator> conv(new DepthwiseConvOperator());
-  const string conv_input = "conv_input";
-  const string conv_filter = "conv_filter";
-  const string conv_output = "conv_output";
+  const std::string conv_input = "conv_input";
+  const std::string conv_filter = "conv_filter";
+  const std::string conv_output = "conv_output";
   conv->inputs.push_back(conv_input);
   conv->inputs.push_back(conv_filter);
   conv->outputs.push_back(conv_output);
@@ -77,10 +77,10 @@ TEST(OpVersionTest, MinimumVersionForMultipleOpVersions) {
   // FullyConnected op with kShuffled4x16Int8 weight format is introduced from
   // '1.10.0'.
   std::unique_ptr<FullyConnectedOperator> fc(new FullyConnectedOperator());
-  const string fc_input = "fc_input";
-  const string fc_weights = "fc_weights";
-  const string fc_bias = "fc_bias";
-  const string fc_output = "fc_output";
+  const std::string fc_input = "fc_input";
+  const std::string fc_weights = "fc_weights";
+  const std::string fc_bias = "fc_bias";
+  const std::string fc_output = "fc_output";
   fc->inputs.push_back(fc_input);
   fc->inputs.push_back(fc_weights);
   fc->inputs.push_back(fc_bias);
@@ -121,10 +121,10 @@ TEST(OpVersionTest, MinimumVersionForMixedOpVersions) {
   // FullyConnected op with kShuffled4x16Int8 weight format is introduced from
   // '1.10.0'.
   std::unique_ptr<FullyConnectedOperator> fc(new FullyConnectedOperator());
-  const string fc_input = "fc_input";
-  const string fc_weights = "fc_weights";
-  const string fc_bias = "fc_bias";
-  const string fc_output = "fc_output";
+  const std::string fc_input = "fc_input";
+  const std::string fc_weights = "fc_weights";
+  const std::string fc_bias = "fc_bias";
+  const std::string fc_output = "fc_output";
   fc->inputs.push_back(fc_input);
   fc->inputs.push_back(fc_weights);
   fc->inputs.push_back(fc_bias);
diff --git a/tensorflow/lite/toco/tflite/operator.cc b/tensorflow/lite/toco/tflite/operator.cc
index fee10a19787..be539cf6054 100644
--- a/tensorflow/lite/toco/tflite/operator.cc
+++ b/tensorflow/lite/toco/tflite/operator.cc
@@ -238,7 +238,7 @@ class SpaceToBatchND
                    TocoOperator* op) const override {}
 
   int GetVersion(const OperatorSignature& op_signature) const override {
-    const string& input_name = op_signature.op->inputs[0];
+    const std::string& input_name = op_signature.op->inputs[0];
     const Array& input_array = op_signature.model->GetArray(input_name);
     ::tflite::OpSignature op_sig =
         GetVersioningOpSig(builtin_op(), op_signature);
@@ -268,8 +268,8 @@ class Sub : public BuiltinOperator<SubOperator, ::tflite::SubOptions,
   }
 
   int GetVersion(const OperatorSignature& op_signature) const override {
-    const string& input1_name = op_signature.op->inputs[0];
-    const string& input2_name = op_signature.op->inputs[1];
+    const std::string& input1_name = op_signature.op->inputs[0];
+    const std::string& input2_name = op_signature.op->inputs[1];
     const Array& input1_array = op_signature.model->GetArray(input1_name);
     const Array& input2_array = op_signature.model->GetArray(input2_name);
     ::tflite::OpSignature op_sig =
@@ -305,8 +305,8 @@ class Div : public BuiltinOperator<DivOperator, ::tflite::DivOptions,
   }
 
   int GetVersion(const OperatorSignature& op_signature) const override {
-    const string& input1_name = op_signature.op->inputs[0];
-    const string& input2_name = op_signature.op->inputs[1];
+    const std::string& input1_name = op_signature.op->inputs[0];
+    const std::string& input2_name = op_signature.op->inputs[1];
     const Array& input1_array = op_signature.model->GetArray(input1_name);
     const Array& input2_array = op_signature.model->GetArray(input2_name);
     ::tflite::OpSignature op_sig =
@@ -339,7 +339,7 @@ class BatchToSpaceND
                    TocoOperator* op) const override {}
 
   int GetVersion(const OperatorSignature& op_signature) const override {
-    const string& input_name = op_signature.op->inputs[0];
+    const std::string& input_name = op_signature.op->inputs[0];
     const Array& input_array = op_signature.model->GetArray(input_name);
     ::tflite::OpSignature op_sig =
         GetVersioningOpSig(builtin_op(), op_signature);
@@ -662,9 +662,9 @@ class Mul : public BuiltinOperator<MulOperator, ::tflite::MulOptions,
   }
 
   int GetVersion(const OperatorSignature& op_signature) const override {
-    const string& input1_name = op_signature.op->inputs[0];
-    const string& input2_name = op_signature.op->inputs[1];
-    const string& output_name = op_signature.op->outputs[0];
+    const std::string& input1_name = op_signature.op->inputs[0];
+    const std::string& input2_name = op_signature.op->inputs[1];
+    const std::string& output_name = op_signature.op->outputs[0];
     const Array& input1_array = op_signature.model->GetArray(input1_name);
     const Array& input2_array = op_signature.model->GetArray(input2_name);
     const Array& output_array = op_signature.model->GetArray(output_name);
@@ -1440,7 +1440,7 @@ class Unpack : public BuiltinOperator<UnpackOperator, ::tflite::UnpackOptions,
   }
 
   int GetVersion(const OperatorSignature& op_signature) const override {
-    const string& input_name = op_signature.op->inputs[0];
+    const std::string& input_name = op_signature.op->inputs[0];
     const Array& input_array = op_signature.model->GetArray(input_name);
     // If the op take int8/uint8 input, it is version 2.
     if (input_array.data_type == ArrayDataType::kInt8 ||
@@ -1577,7 +1577,7 @@ class Where : public BuiltinOperator<WhereOperator, ::tflite::WhereOptions,
 };
 
 std::unique_ptr<flexbuffers::Builder> WriteFlexOpOptions(
-    const string& tensorflow_node_def) {
+    const std::string& tensorflow_node_def) {
   auto fbb = absl::make_unique<flexbuffers::Builder>();
 
   ::tensorflow::NodeDef node_def;
@@ -1597,7 +1597,7 @@ std::unique_ptr<flexbuffers::Builder> WriteFlexOpOptions(
 
 class TensorFlowUnsupported : public BaseOperator {
  public:
-  TensorFlowUnsupported(const string& name, OperatorType type,
+  TensorFlowUnsupported(const std::string& name, OperatorType type,
                         bool enable_select_tf_ops)
       : BaseOperator(name, type), enable_select_tf_ops_(enable_select_tf_ops) {}
 
@@ -1676,7 +1676,7 @@ class TensorFlowUnsupported : public BaseOperator {
         case tensorflow::AttrValue::kList:
           if (attr.list().s_size() > 0) {
             auto start = fbb->StartVector(key);
-            for (const string& v : attr.list().s()) {
+            for (const std::string& v : attr.list().s()) {
               fbb->Add(v);
             }
             fbb->EndVector(start, /*typed=*/true, /*fixed=*/false);
@@ -1736,10 +1736,11 @@ class TensorFlowUnsupported : public BaseOperator {
           break;
         case flexbuffers::FBT_BOOL:
           (*attr)[key].set_b(value.AsBool());
-          if (string(key) == "_output_quantized") {
+          if (std::string(key) == "_output_quantized") {
             op->quantized = value.AsBool();
           }
-          if (string(key) == "_support_output_type_float_in_quantized_op") {
+          if (std::string(key) ==
+              "_support_output_type_float_in_quantized_op") {
             op->support_output_type_float_in_quantized_op = value.AsBool();
           }
           break;
@@ -2095,9 +2096,9 @@ std::map<OperatorType, std::unique_ptr<BaseOperator>> BuildOperatorByTypeMap(
   return result;
 }
 
-std::map<string, std::unique_ptr<BaseOperator>> BuildOperatorByNameMap(
+std::map<std::string, std::unique_ptr<BaseOperator>> BuildOperatorByNameMap(
     bool enable_select_tf_ops) {
-  std::map<string, std::unique_ptr<BaseOperator>> result;
+  std::map<std::string, std::unique_ptr<BaseOperator>> result;
 
   std::vector<std::unique_ptr<BaseOperator>> ops =
       BuildOperatorList(enable_select_tf_ops);
@@ -2109,7 +2110,7 @@ std::map<string, std::unique_ptr<BaseOperator>> BuildOperatorByNameMap(
 }
 
 bool ShouldExportAsFlexOp(bool enable_select_tf_ops,
-                          const string& tensorflow_op_name) {
+                          const std::string& tensorflow_op_name) {
   // If Flex ops aren't allow at all, simply return false.
   if (!enable_select_tf_ops) {
     return false;
diff --git a/tensorflow/lite/toco/tflite/operator.h b/tensorflow/lite/toco/tflite/operator.h
index 19d92145e0c..fb79b97f46e 100644
--- a/tensorflow/lite/toco/tflite/operator.h
+++ b/tensorflow/lite/toco/tflite/operator.h
@@ -30,7 +30,7 @@ class BaseOperator;
 // Return a map contained all know TF Lite Operators, keyed by their names.
 // TODO(ycling): The pattern to propagate parameters (e.g. enable_select_tf_ops)
 // is ugly here. Consider refactoring.
-std::map<string, std::unique_ptr<BaseOperator>> BuildOperatorByNameMap(
+std::map<std::string, std::unique_ptr<BaseOperator>> BuildOperatorByNameMap(
     bool enable_select_tf_ops = false);
 
 // Return a map contained all know TF Lite Operators, keyed by the type of
@@ -41,7 +41,7 @@ std::map<OperatorType, std::unique_ptr<BaseOperator>> BuildOperatorByTypeMap(
 // Write the custom option FlexBuffer with a serialized TensorFlow NodeDef
 // for a Flex op.
 std::unique_ptr<flexbuffers::Builder> WriteFlexOpOptions(
-    const string& tensorflow_node_def);
+    const std::string& tensorflow_node_def);
 
 // These are the flatbuffer types for custom and builtin options.
 using CustomOptions = flatbuffers::Vector<uint8_t>;
@@ -71,11 +71,11 @@ struct Options {
 class BaseOperator {
  public:
   // Build an operator with the given TF Lite name and tf.mini type.
-  BaseOperator(const string& name, OperatorType type)
+  BaseOperator(const std::string& name, OperatorType type)
       : name_(name), type_(type) {}
   virtual ~BaseOperator() = default;
 
-  string name() const { return name_; }
+  std::string name() const { return name_; }
   OperatorType type() const { return type_; }
 
   // Given a tf.mini operator, create the corresponding flatbuffer options and
@@ -111,7 +111,7 @@ class BaseOperator {
   }
 
  private:
-  string name_;
+  std::string name_;
   OperatorType type_;
 };
 
@@ -123,7 +123,7 @@ class BaseOperator {
 // Helper function to determine if a unsupported TensorFlow op should be
 // exported as an Flex op or a regular custom op.
 bool ShouldExportAsFlexOp(bool enable_select_tf_ops,
-                          const string& tensorflow_op_name);
+                          const std::string& tensorflow_op_name);
 
 }  // namespace tflite
 
diff --git a/tensorflow/lite/toco/tflite/operator_test.cc b/tensorflow/lite/toco/tflite/operator_test.cc
index a4fe01e4afd..cb466fef079 100644
--- a/tensorflow/lite/toco/tflite/operator_test.cc
+++ b/tensorflow/lite/toco/tflite/operator_test.cc
@@ -30,8 +30,8 @@ namespace {
 class OperatorTest : public ::testing::Test {
  protected:
   // Return the operator for the given name and type.
-  const BaseOperator& GetOperator(const string& name, OperatorType type) {
-    using OpsByName = std::map<string, std::unique_ptr<BaseOperator>>;
+  const BaseOperator& GetOperator(const std::string& name, OperatorType type) {
+    using OpsByName = std::map<std::string, std::unique_ptr<BaseOperator>>;
     using OpsByType = std::map<OperatorType, std::unique_ptr<BaseOperator>>;
 
     static auto* by_name = new OpsByName(BuildOperatorByNameMap());
@@ -86,7 +86,7 @@ class OperatorTest : public ::testing::Test {
   // Verify serialization and deserialization of simple operators (those
   // that don't have any configuration parameters).
   template <typename T>
-  void CheckSimpleOperator(const string& name, OperatorType type) {
+  void CheckSimpleOperator(const std::string& name, OperatorType type) {
     Options options;
     auto output_toco_op =
         SerializeAndDeserialize(GetOperator(name, type), T(), &options);
@@ -99,7 +99,7 @@ class OperatorTest : public ::testing::Test {
   }
 
   template <typename T>
-  void CheckReducerOperator(const string& name, OperatorType type) {
+  void CheckReducerOperator(const std::string& name, OperatorType type) {
     T op;
 
     op.keep_dims = false;
diff --git a/tensorflow/lite/toco/tflite/types.cc b/tensorflow/lite/toco/tflite/types.cc
index 96cad557baf..9d4ab8434d1 100644
--- a/tensorflow/lite/toco/tflite/types.cc
+++ b/tensorflow/lite/toco/tflite/types.cc
@@ -25,7 +25,7 @@ DataBuffer::FlatBufferOffset CopyStringToBuffer(
     const Array& array, flatbuffers::FlatBufferBuilder* builder) {
   const auto& src_data = array.GetBuffer<ArrayDataType::kString>().data;
   ::tflite::DynamicBuffer dyn_buffer;
-  for (const string& str : src_data) {
+  for (const std::string& str : src_data) {
     dyn_buffer.AddString(str.c_str(), str.length());
   }
   char* tensor_buffer;
@@ -58,12 +58,12 @@ DataBuffer::FlatBufferOffset CopyBuffer(
 
 void CopyStringFromBuffer(const ::tflite::Buffer& buffer, Array* array) {
   auto* src_data = reinterpret_cast<const char*>(buffer.data()->data());
-  std::vector<string>* dst_data =
+  std::vector<std::string>* dst_data =
       &array->GetMutableBuffer<ArrayDataType::kString>().data;
   int32_t num_strings = ::tflite::GetStringCount(src_data);
   for (int i = 0; i < num_strings; i++) {
     ::tflite::StringRef str_ref = ::tflite::GetString(src_data, i);
-    string this_str(str_ref.str, str_ref.len);
+    std::string this_str(str_ref.str, str_ref.len);
     dst_data->push_back(this_str);
   }
 }