replace implicit use of cartographer::string with explicit use of std::string (#673)

Fixes #622.

cartographer/common/configuration_file_resolver.cc

@@ -27,14 +27,15 @@ namespace cartographer {
 namespace common {
 
 ConfigurationFileResolver::ConfigurationFileResolver(
-    const std::vector<string>& configuration_files_directories)
+    const std::vector<std::string>& configuration_files_directories)
     : configuration_files_directories_(configuration_files_directories) {
   configuration_files_directories_.push_back(kConfigurationFilesDirectory);
 }
 
-string ConfigurationFileResolver::GetFullPathOrDie(const string& basename) {
+std::string ConfigurationFileResolver::GetFullPathOrDie(
+    const std::string& basename) {
   for (const auto& path : configuration_files_directories_) {
-    const string filename = path + "/" + basename;
+    const std::string filename = path + "/" + basename;
     std::ifstream stream(filename.c_str());
     if (stream.good()) {
       LOG(INFO) << "Found '" << filename << "' for '" << basename << "'.";
@@ -44,10 +45,11 @@ string ConfigurationFileResolver::GetFullPathOrDie(const string& basename) {
   LOG(FATAL) << "File '" << basename << "' was not found.";
 }
 
-string ConfigurationFileResolver::GetFileContentOrDie(const string& basename) {
+std::string ConfigurationFileResolver::GetFileContentOrDie(
-  const string filename = GetFullPathOrDie(basename);
+    const std::string& basename) {
+  const std::string filename = GetFullPathOrDie(basename);
   std::ifstream stream(filename.c_str());
-  return string((std::istreambuf_iterator<char>(stream)),
+  return std::string((std::istreambuf_iterator<char>(stream)),
                      std::istreambuf_iterator<char>());
 }
 

cartographer/common/configuration_file_resolver.h

@@ -34,13 +34,13 @@ namespace common {
 class ConfigurationFileResolver : public FileResolver {
  public:
   explicit ConfigurationFileResolver(
-      const std::vector<string>& configuration_files_directories);
+      const std::vector<std::string>& configuration_files_directories);
 
-  string GetFullPathOrDie(const string& basename) override;
+  std::string GetFullPathOrDie(const std::string& basename) override;
-  string GetFileContentOrDie(const string& basename) override;
+  std::string GetFileContentOrDie(const std::string& basename) override;
 
  private:
-  std::vector<string> configuration_files_directories_;
+  std::vector<std::string> configuration_files_directories_;
 };
 
 }  // namespace common

cartographer/common/configuration_files_test.cc

@@ -23,20 +23,19 @@
 #include "cartographer/mapping/map_builder.h"
 #include "gtest/gtest.h"
 
-using std::string;
-
 namespace cartographer_ros {
 namespace {
 
 TEST(ConfigurationFilesTest, ValidateMapBuilderOptions) {
-  const string kCode = R"text(
+  const std::string kCode = R"text(
       include "map_builder.lua"
       MAP_BUILDER.use_trajectory_builder_2d = true
       return MAP_BUILDER)text";
   EXPECT_NO_FATAL_FAILURE({
     auto file_resolver = ::cartographer::common::make_unique<
         ::cartographer::common::ConfigurationFileResolver>(
-        std::vector<string>{string(::cartographer::common::kSourceDirectory) +
+        std::vector<std::string>{
+            std::string(::cartographer::common::kSourceDirectory) +
             "/configuration_files"});
     ::cartographer::common::LuaParameterDictionary lua_parameter_dictionary(
         kCode, std::move(file_resolver));
@@ -45,14 +44,15 @@ TEST(ConfigurationFilesTest, ValidateMapBuilderOptions) {
 }
 
 TEST(ConfigurationFilesTest, ValidateTrajectoryBuilderOptions) {
-  const string kCode = R"text(
+  const std::string kCode = R"text(
       include "trajectory_builder.lua"
       TRAJECTORY_BUILDER.trajectory_builder_2d.use_imu_data = false
       return TRAJECTORY_BUILDER)text";
   EXPECT_NO_FATAL_FAILURE({
     auto file_resolver = ::cartographer::common::make_unique<
         ::cartographer::common::ConfigurationFileResolver>(
-        std::vector<string>{string(::cartographer::common::kSourceDirectory) +
+        std::vector<std::string>{
+            std::string(::cartographer::common::kSourceDirectory) +
             "/configuration_files"});
     ::cartographer::common::LuaParameterDictionary lua_parameter_dictionary(
         kCode, std::move(file_resolver));

cartographer/common/fixed_ratio_sampler.cc

@@ -37,7 +37,7 @@ bool FixedRatioSampler::Pulse() {
   return false;
 }
 
-string FixedRatioSampler::DebugString() {
+std::string FixedRatioSampler::DebugString() {
   return std::to_string(num_samples_) + " (" +
          std::to_string(100. * num_samples_ / num_pulses_) + "%)";
 }

cartographer/common/fixed_ratio_sampler.h

@@ -38,7 +38,7 @@ class FixedRatioSampler {
   bool Pulse();
 
   // Returns a debug string describing the current ratio of samples to pulses.
-  string DebugString();
+  std::string DebugString();
 
  private:
   // Sampling occurs if the proportion of samples to pulses drops below this

cartographer/common/histogram.cc

@@ -28,7 +28,7 @@ namespace common {
 
 void Histogram::Add(const float value) { values_.push_back(value); }
 
-string Histogram::ToString(const int buckets) const {
+std::string Histogram::ToString(const int buckets) const {
   CHECK_GE(buckets, 1);
   if (values_.empty()) {
     return "Count: 0";
@@ -37,7 +37,7 @@ string Histogram::ToString(const int buckets) const {
   const float max = *std::max_element(values_.begin(), values_.end());
   const float mean =
       std::accumulate(values_.begin(), values_.end(), 0.f) / values_.size();
-  string result = "Count: " + std::to_string(values_.size()) +
+  std::string result = "Count: " + std::to_string(values_.size()) +
                        "  Min: " + std::to_string(min) +
                        "  Max: " + std::to_string(max) +
                        "  Mean: " + std::to_string(mean);

cartographer/common/histogram.h

@@ -28,7 +28,7 @@ namespace common {
 class Histogram {
  public:
   void Add(float value);
-  string ToString(int buckets) const;
+  std::string ToString(int buckets) const;
 
  private:
   std::vector<float> values_;

cartographer/common/lua_parameter_dictionary.cc

@@ -99,7 +99,7 @@ int LuaChoose(lua_State* L) {
 
 // Pushes a value to the Lua stack.
 void PushValue(lua_State* L, const int key) { lua_pushinteger(L, key); }
-void PushValue(lua_State* L, const string& key) {
+void PushValue(lua_State* L, const std::string& key) {
   lua_pushstring(L, key.c_str());
 }
 
@@ -147,18 +147,18 @@ void GetArrayValues(lua_State* L, const std::function<void()>& pop_value) {
 
 std::unique_ptr<LuaParameterDictionary>
 LuaParameterDictionary::NonReferenceCounted(
-    const string& code, std::unique_ptr<FileResolver> file_resolver) {
+    const std::string& code, std::unique_ptr<FileResolver> file_resolver) {
   return std::unique_ptr<LuaParameterDictionary>(new LuaParameterDictionary(
       code, ReferenceCount::NO, std::move(file_resolver)));
 }
 
 LuaParameterDictionary::LuaParameterDictionary(
-    const string& code, std::unique_ptr<FileResolver> file_resolver)
+    const std::string& code, std::unique_ptr<FileResolver> file_resolver)
     : LuaParameterDictionary(code, ReferenceCount::YES,
                              std::move(file_resolver)) {}
 
 LuaParameterDictionary::LuaParameterDictionary(
-    const string& code, ReferenceCount reference_count,
+    const std::string& code, ReferenceCount reference_count,
     std::unique_ptr<FileResolver> file_resolver)
     : L_(luaL_newstate()),
       index_into_reference_table_(-1),
@@ -206,9 +206,9 @@ LuaParameterDictionary::~LuaParameterDictionary() {
   }
 }
 
-std::vector<string> LuaParameterDictionary::GetKeys() const {
+std::vector<std::string> LuaParameterDictionary::GetKeys() const {
   CheckTableIsAtTopOfStack(L_);
-  std::vector<string> keys;
+  std::vector<std::string> keys;
 
   lua_pushnil(L_);  // Push the first key
   while (lua_next(L_, -2) != 0) {
@@ -220,28 +220,28 @@ std::vector<string> LuaParameterDictionary::GetKeys() const {
   return keys;
 }
 
-bool LuaParameterDictionary::HasKey(const string& key) const {
+bool LuaParameterDictionary::HasKey(const std::string& key) const {
   return HasKeyOfType(L_, key);
 }
 
-string LuaParameterDictionary::GetString(const string& key) {
+std::string LuaParameterDictionary::GetString(const std::string& key) {
   CheckHasKeyAndReference(key);
   GetValueFromLuaTable(L_, key);
   return PopString(Quoted::NO);
 }
 
-string LuaParameterDictionary::PopString(Quoted quoted) const {
+std::string LuaParameterDictionary::PopString(Quoted quoted) const {
   CHECK(lua_isstring(L_, -1)) << "Top of stack is not a string value.";
   if (quoted == Quoted::YES) {
     QuoteStringOnStack(L_);
   }
 
-  const string value = lua_tostring(L_, -1);
+  const std::string value = lua_tostring(L_, -1);
   lua_pop(L_, 1);
   return value;
 }
 
-double LuaParameterDictionary::GetDouble(const string& key) {
+double LuaParameterDictionary::GetDouble(const std::string& key) {
   CheckHasKeyAndReference(key);
   GetValueFromLuaTable(L_, key);
   return PopDouble();
@@ -254,7 +254,7 @@ double LuaParameterDictionary::PopDouble() const {
   return value;
 }
 
-int LuaParameterDictionary::GetInt(const string& key) {
+int LuaParameterDictionary::GetInt(const std::string& key) {
   CheckHasKeyAndReference(key);
   GetValueFromLuaTable(L_, key);
   return PopInt();
@@ -267,7 +267,7 @@ int LuaParameterDictionary::PopInt() const {
   return value;
 }
 
-bool LuaParameterDictionary::GetBool(const string& key) {
+bool LuaParameterDictionary::GetBool(const std::string& key) {
   CheckHasKeyAndReference(key);
   GetValueFromLuaTable(L_, key);
   return PopBool();
@@ -281,7 +281,7 @@ bool LuaParameterDictionary::PopBool() const {
 }
 
 std::unique_ptr<LuaParameterDictionary> LuaParameterDictionary::GetDictionary(
-    const string& key) {
+    const std::string& key) {
   CheckHasKeyAndReference(key);
   GetValueFromLuaTable(L_, key);
   return PopDictionary(reference_count_);
@@ -297,12 +297,13 @@ std::unique_ptr<LuaParameterDictionary> LuaParameterDictionary::PopDictionary(
   return value;
 }
 
-string LuaParameterDictionary::DoToString(const string& indent) const {
+std::string LuaParameterDictionary::DoToString(
-  string result = "{";
+    const std::string& indent) const {
+  std::string result = "{";
   bool dictionary_is_empty = true;
 
   const auto top_of_stack_to_string = [this, indent,
-                                       &dictionary_is_empty]() -> string {
+                                       &dictionary_is_empty]() -> std::string {
     dictionary_is_empty = false;
 
     const int value_type = lua_type(L_, -1);
@@ -346,10 +347,10 @@ string LuaParameterDictionary::DoToString(const string& indent) const {
   }
 
   // String keys.
-  std::vector<string> keys = GetKeys();
+  std::vector<std::string> keys = GetKeys();
   if (!keys.empty()) {
     std::sort(keys.begin(), keys.end());
-    for (const string& key : keys) {
+    for (const std::string& key : keys) {
       GetValueFromLuaTable(L_, key);
       result.append("\n");
       result.append(indent);
@@ -370,7 +371,7 @@ string LuaParameterDictionary::DoToString(const string& indent) const {
   return result;
 }
 
-string LuaParameterDictionary::ToString() const { return DoToString(""); }
+std::string LuaParameterDictionary::ToString() const { return DoToString(""); }
 
 std::vector<double> LuaParameterDictionary::GetArrayValuesAsDoubles() {
   std::vector<double> values;
@@ -387,19 +388,19 @@ LuaParameterDictionary::GetArrayValuesAsDictionaries() {
   return values;
 }
 
-std::vector<string> LuaParameterDictionary::GetArrayValuesAsStrings() {
+std::vector<std::string> LuaParameterDictionary::GetArrayValuesAsStrings() {
-  std::vector<string> values;
+  std::vector<std::string> values;
   GetArrayValues(L_,
                  [&values, this] { values.push_back(PopString(Quoted::NO)); });
   return values;
 }
 
-void LuaParameterDictionary::CheckHasKey(const string& key) const {
+void LuaParameterDictionary::CheckHasKey(const std::string& key) const {
   CHECK(HasKey(key)) << "Key '" << key << "' not in dictionary:\n"
                      << ToString();
 }
 
-void LuaParameterDictionary::CheckHasKeyAndReference(const string& key) {
+void LuaParameterDictionary::CheckHasKeyAndReference(const std::string& key) {
   CheckHasKey(key);
   reference_counts_[key]++;
 }
@@ -414,7 +415,7 @@ void LuaParameterDictionary::CheckAllKeysWereUsedExactlyOnceAndReset() {
   reference_counts_.clear();
 }
 
-int LuaParameterDictionary::GetNonNegativeInt(const string& key) {
+int LuaParameterDictionary::GetNonNegativeInt(const std::string& key) {
   const int temp = GetInt(key);  // Will increase reference count.
   CHECK_GE(temp, 0) << temp << " is negative.";
   return temp;
@@ -427,15 +428,16 @@ int LuaParameterDictionary::LuaInclude(lua_State* L) {
   CHECK(lua_isstring(L, -1)) << "include takes a filename.";
 
   LuaParameterDictionary* parameter_dictionary = GetDictionaryFromRegistry(L);
-  const string basename = lua_tostring(L, -1);
+  const std::string basename = lua_tostring(L, -1);
-  const string filename =
+  const std::string filename =
       parameter_dictionary->file_resolver_->GetFullPathOrDie(basename);
   if (std::find(parameter_dictionary->included_files_.begin(),
                 parameter_dictionary->included_files_.end(),
                 filename) != parameter_dictionary->included_files_.end()) {
-    string error_msg = "Tried to include " + filename +
+    std::string error_msg =
+        "Tried to include " + filename +
         " twice. Already included files in order of inclusion: ";
-    for (const string& filename : parameter_dictionary->included_files_) {
+    for (const std::string& filename : parameter_dictionary->included_files_) {
       error_msg.append(filename);
       error_msg.append("\n");
     }
@@ -445,7 +447,7 @@ int LuaParameterDictionary::LuaInclude(lua_State* L) {
   lua_pop(L, 1);
   CHECK_EQ(lua_gettop(L), 0);
 
-  const string content =
+  const std::string content =
       parameter_dictionary->file_resolver_->GetFileContentOrDie(basename);
   CheckForLuaErrors(
       L, luaL_loadbuffer(L, content.c_str(), content.size(), filename.c_str()));
@@ -460,7 +462,7 @@ int LuaParameterDictionary::LuaRead(lua_State* L) {
   CHECK(lua_isstring(L, -1)) << "read takes a filename.";
 
   LuaParameterDictionary* parameter_dictionary = GetDictionaryFromRegistry(L);
-  const string file_content =
+  const std::string file_content =
       parameter_dictionary->file_resolver_->GetFileContentOrDie(
           lua_tostring(L, -1));
   lua_pushstring(L, file_content.c_str());

cartographer/common/lua_parameter_dictionary.h

@@ -34,15 +34,15 @@ namespace common {
 class FileResolver {
  public:
   virtual ~FileResolver() {}
-  virtual string GetFullPathOrDie(const string& basename) = 0;
+  virtual std::string GetFullPathOrDie(const std::string& basename) = 0;
-  virtual string GetFileContentOrDie(const string& basename) = 0;
+  virtual std::string GetFileContentOrDie(const std::string& basename) = 0;
 };
 
 // A parameter dictionary that gets loaded from Lua code.
 class LuaParameterDictionary {
  public:
   // Constructs the dictionary from a Lua Table specification.
-  LuaParameterDictionary(const string& code,
+  LuaParameterDictionary(const std::string& code,
                          std::unique_ptr<FileResolver> file_resolver);
 
   LuaParameterDictionary(const LuaParameterDictionary&) = delete;
@@ -50,38 +50,39 @@ class LuaParameterDictionary {
 
   // Constructs a LuaParameterDictionary without reference counting.
   static std::unique_ptr<LuaParameterDictionary> NonReferenceCounted(
-      const string& code, std::unique_ptr<FileResolver> file_resolver);
+      const std::string& code, std::unique_ptr<FileResolver> file_resolver);
 
   ~LuaParameterDictionary();
 
   // Returns all available keys.
-  std::vector<string> GetKeys() const;
+  std::vector<std::string> GetKeys() const;
 
   // Returns true if the key is in this dictionary.
-  bool HasKey(const string& key) const;
+  bool HasKey(const std::string& key) const;
 
   // These methods CHECK() that the 'key' exists.
-  string GetString(const string& key);
+  std::string GetString(const std::string& key);
-  double GetDouble(const string& key);
+  double GetDouble(const std::string& key);
-  int GetInt(const string& key);
+  int GetInt(const std::string& key);
-  bool GetBool(const string& key);
+  bool GetBool(const std::string& key);
-  std::unique_ptr<LuaParameterDictionary> GetDictionary(const string& key);
+  std::unique_ptr<LuaParameterDictionary> GetDictionary(const std::string& key);
 
   // Gets an int from the dictionary and CHECK()s that it is non-negative.
-  int GetNonNegativeInt(const string& key);
+  int GetNonNegativeInt(const std::string& key);
 
   // Returns a string representation for this LuaParameterDictionary.
-  string ToString() const;
+  std::string ToString() const;
 
   // Returns the values of the keys '1', '2', '3' as the given types.
   std::vector<double> GetArrayValuesAsDoubles();
-  std::vector<string> GetArrayValuesAsStrings();
+  std::vector<std::string> GetArrayValuesAsStrings();
   std::vector<std::unique_ptr<LuaParameterDictionary>>
   GetArrayValuesAsDictionaries();
 
  private:
   enum class ReferenceCount { YES, NO };
-  LuaParameterDictionary(const string& code, ReferenceCount reference_count,
+  LuaParameterDictionary(const std::string& code,
+                         ReferenceCount reference_count,
                          std::unique_ptr<FileResolver> file_resolver);
 
   // For GetDictionary().
@@ -89,7 +90,7 @@ class LuaParameterDictionary {
                          std::shared_ptr<FileResolver> file_resolver);
 
   // Function that recurses to keep track of indent for ToString().
-  string DoToString(const string& indent) const;
+  std::string DoToString(const std::string& indent) const;
 
   // Pop the top of the stack and CHECKs that the type is correct.
   double PopDouble() const;
@@ -100,7 +101,7 @@ class LuaParameterDictionary {
   // is either quoted to be suitable to be read back by a Lua interpretor or
   // not.
   enum class Quoted { YES, NO };
-  string PopString(Quoted quoted) const;
+  std::string PopString(Quoted quoted) const;
 
   // Creates a LuaParameterDictionary from the Lua table at the top of the
   // stack, either with or without reference counting.
@@ -108,10 +109,10 @@ class LuaParameterDictionary {
       ReferenceCount reference_count) const;
 
   // CHECK() that 'key' is in the dictionary.
-  void CheckHasKey(const string& key) const;
+  void CheckHasKey(const std::string& key) const;
 
   // CHECK() that 'key' is in this dictionary and reference it as being used.
-  void CheckHasKeyAndReference(const string& key);
+  void CheckHasKeyAndReference(const std::string& key);
 
   // If desired, this can be called in the destructor of a derived class. It
   // will CHECK() that all keys defined in the configuration have been used
@@ -135,11 +136,11 @@ class LuaParameterDictionary {
 
   // This is modified with every call to Get* in order to verify that all
   // parameters are read exactly once.
-  std::map<string, int> reference_counts_;
+  std::map<std::string, int> reference_counts_;
 
   // List of all included files in order of inclusion. Used to prevent double
   // inclusion.
-  std::vector<string> included_files_;
+  std::vector<std::string> included_files_;
 };
 
 }  // namespace common

cartographer/common/lua_parameter_dictionary_test.cc

@@ -29,7 +29,7 @@ namespace common {
 namespace {
 
 std::unique_ptr<LuaParameterDictionary> MakeNonReferenceCounted(
-    const string& code) {
+    const std::string& code) {
   return LuaParameterDictionary::NonReferenceCounted(
       code, common::make_unique<DummyFileResolver>());
 }
@@ -37,7 +37,7 @@ std::unique_ptr<LuaParameterDictionary> MakeNonReferenceCounted(
 class LuaParameterDictionaryTest : public ::testing::Test {
  protected:
   void ReferenceAllKeysAsIntegers(LuaParameterDictionary* dict) {
-    for (const string& key : dict->GetKeys()) {
+    for (const std::string& key : dict->GetKeys()) {
       dict->GetInt(key);
     }
   }
@@ -73,7 +73,7 @@ TEST_F(LuaParameterDictionaryTest, GetDictionary) {
       MakeDictionary("return { blah = { blue = 100, red = 200 }, fasel = 10 }");
 
   std::unique_ptr<LuaParameterDictionary> sub_dict(dict->GetDictionary("blah"));
-  std::vector<string> keys = sub_dict->GetKeys();
+  std::vector<std::string> keys = sub_dict->GetKeys();
   ASSERT_EQ(keys.size(), 2);
   std::sort(keys.begin(), keys.end());
   ASSERT_EQ(keys[0], "blue");
@@ -89,7 +89,7 @@ TEST_F(LuaParameterDictionaryTest, GetDictionary) {
 TEST_F(LuaParameterDictionaryTest, GetKeys) {
   auto dict = MakeDictionary("return { blah = 100, blah1 = 200}");
 
-  std::vector<string> keys = dict->GetKeys();
+  std::vector<std::string> keys = dict->GetKeys();
   ASSERT_EQ(keys.size(), 2);
   std::sort(keys.begin(), keys.end());
   ASSERT_EQ(keys[0], "blah");
@@ -122,7 +122,7 @@ TEST_F(LuaParameterDictionaryTest, ToString) {
   alpha1 = false,
   })");
 
-  const string golden = R"({
+  const std::string golden = R"({
   alpha = true,
   alpha1 = false,
   blub = "hello",
@@ -164,7 +164,7 @@ TEST_F(LuaParameterDictionaryTest, ToStringForArrays) {
       foo = "ups",
   })");
 
-  const string golden = R"({
+  const std::string golden = R"({
   "blub",
   3.000000,
   3.100000,
@@ -176,7 +176,7 @@ TEST_F(LuaParameterDictionaryTest, ToStringForArrays) {
 TEST_F(LuaParameterDictionaryTest, GetArrayValuesAsStrings) {
   auto dict = MakeDictionary("return { 'a', 'b', 'c' }");
   EXPECT_EQ(0, dict->GetKeys().size());
-  const std::vector<string> values = dict->GetArrayValuesAsStrings();
+  const std::vector<std::string> values = dict->GetArrayValuesAsStrings();
   EXPECT_EQ(3, values.size());
   EXPECT_EQ("a", values[0]);
   EXPECT_EQ("b", values[1]);

cartographer/common/lua_parameter_dictionary_test_helpers.h

@@ -37,16 +37,17 @@ class DummyFileResolver : public FileResolver {
 
   ~DummyFileResolver() override {}
 
-  string GetFileContentOrDie(const string& unused_basename) override {
+  std::string GetFileContentOrDie(const std::string& unused_basename) override {
     LOG(FATAL) << "Not implemented";
   }
 
-  string GetFullPathOrDie(const string& unused_basename) override {
+  std::string GetFullPathOrDie(const std::string& unused_basename) override {
     LOG(FATAL) << "Not implemented";
   }
 };
 
-std::unique_ptr<LuaParameterDictionary> MakeDictionary(const string& code) {
+std::unique_ptr<LuaParameterDictionary> MakeDictionary(
+    const std::string& code) {
   return common::make_unique<LuaParameterDictionary>(
       code, common::make_unique<DummyFileResolver>());
 }

cartographer/common/port.h

@@ -36,8 +36,6 @@ using uint16 = uint16_t;
 using uint32 = uint32_t;
 using uint64 = uint64_t;
 
-using std::string;
-
 namespace common {
 
 inline int RoundToInt(const float x) { return std::lround(x); }
@@ -48,7 +46,8 @@ inline int64 RoundToInt64(const float x) { return std::lround(x); }
 
 inline int64 RoundToInt64(const double x) { return std::lround(x); }
 
-inline void FastGzipString(const string& uncompressed, string* compressed) {
+inline void FastGzipString(const std::string& uncompressed,
+                           std::string* compressed) {
   boost::iostreams::filtering_ostream out;
   out.push(
       boost::iostreams::gzip_compressor(boost::iostreams::zlib::best_speed));
@@ -58,7 +57,8 @@ inline void FastGzipString(const string& uncompressed, string* compressed) {
                           uncompressed.size());
 }
 
-inline void FastGunzipString(const string& compressed, string* decompressed) {
+inline void FastGunzipString(const std::string& compressed,
+                             std::string* decompressed) {
   boost::iostreams::filtering_ostream out;
   out.push(boost::iostreams::gzip_decompressor());
   out.push(boost::iostreams::back_inserter(*decompressed));

cartographer/common/rate_timer.h

@@ -78,7 +78,7 @@ class RateTimer {
   }
 
   // Returns a debug string representation.
-  string DebugString() const {
+  std::string DebugString() const {
     if (events_.size() < 2) {
       return "unknown";
     }
@@ -109,7 +109,7 @@ class RateTimer {
   }
 
   // Returns the average and standard deviation of the deltas.
-  string DeltasDebugString() const {
+  std::string DeltasDebugString() const {
     const auto deltas = ComputeDeltasInSeconds();
     const double sum = std::accumulate(deltas.begin(), deltas.end(), 0.);
     const double mean = sum / deltas.size();

cartographer/ground_truth/autogenerate_ground_truth_main.cc

@@ -163,8 +163,8 @@ proto::GroundTruth GenerateGroundTruth(
   return ground_truth;
 }
 
-void Run(const string& pose_graph_filename, const string& output_filename,
+void Run(const std::string& pose_graph_filename,
-         const double min_covered_distance,
+         const std::string& output_filename, const double min_covered_distance,
          const double outlier_threshold_meters,
          const double outlier_threshold_radians) {
   LOG(INFO) << "Reading pose graph from '" << pose_graph_filename << "'...";

cartographer/ground_truth/compute_relations_metrics_main.cc

@@ -67,7 +67,7 @@ Error ComputeError(const transform::Rigid3d& pose1,
                common::Pow2(transform::GetAngle(error))};
 }
 
-string MeanAndStdDevString(const std::vector<double>& values) {
+std::string MeanAndStdDevString(const std::vector<double>& values) {
   CHECK_GE(values.size(), 2);
   const double mean =
       std::accumulate(values.begin(), values.end(), 0.) / values.size();
@@ -80,10 +80,10 @@ string MeanAndStdDevString(const std::vector<double>& values) {
   std::ostringstream out;
   out << std::fixed << std::setprecision(5) << mean << " +/- "
       << standard_deviation;
-  return string(out.str());
+  return std::string(out.str());
 }
 
-string StatisticsString(const std::vector<Error>& errors) {
+std::string StatisticsString(const std::vector<Error>& errors) {
   std::vector<double> translational_errors;
   std::vector<double> squared_translational_errors;
   std::vector<double> rotational_errors_degrees;
@@ -109,7 +109,8 @@ string StatisticsString(const std::vector<Error>& errors) {
          MeanAndStdDevString(squared_rotational_errors_degrees) + " deg^2\n";
 }
 
-void Run(const string& pose_graph_filename, const string& relations_filename,
+void Run(const std::string& pose_graph_filename,
+         const std::string& relations_filename,
          const bool read_text_file_with_unix_timestamps) {
   LOG(INFO) << "Reading pose graph from '" << pose_graph_filename << "'...";
   mapping::proto::SparsePoseGraph pose_graph;

cartographer/ground_truth/relations_text_file.cc

@@ -37,7 +37,8 @@ common::Time UnixToCommonTime(double unix_time) {
 
 }  // namespace
 
-proto::GroundTruth ReadRelationsTextFile(const string& relations_filename) {
+proto::GroundTruth ReadRelationsTextFile(
+    const std::string& relations_filename) {
   proto::GroundTruth ground_truth;
   std::ifstream relations_stream(relations_filename.c_str());
   double unix_time_1, unix_time_2, x, y, z, roll, pitch, yaw;

cartographer/ground_truth/relations_text_file.h

@@ -33,7 +33,7 @@ namespace ground_truth {
 // R. Kuemmerle, B. Steder, C. Dornhege, M. Ruhnke, G. Grisetti, C. Stachniss,
 // and A. Kleiner, "On measuring the accuracy of SLAM algorithms," Autonomous
 // Robots, vol. 27, no. 4, pp. 387–407, 2009.
-proto::GroundTruth ReadRelationsTextFile(const string& relations_filename);
+proto::GroundTruth ReadRelationsTextFile(const std::string& relations_filename);
 
 }  // namespace ground_truth
 }  // namespace cartographer

cartographer/io/coloring_points_processor.cc

@@ -27,7 +27,7 @@ std::unique_ptr<ColoringPointsProcessor>
 ColoringPointsProcessor::FromDictionary(
     common::LuaParameterDictionary* const dictionary,
     PointsProcessor* const next) {
-  const string frame_id = dictionary->GetString("frame_id");
+  const std::string frame_id = dictionary->GetString("frame_id");
   const std::vector<double> color_values =
       dictionary->GetDictionary("color")->GetArrayValuesAsDoubles();
   const Uint8Color color = {{static_cast<uint8>(color_values[0]),
@@ -38,7 +38,7 @@ ColoringPointsProcessor::FromDictionary(
 }
 
 ColoringPointsProcessor::ColoringPointsProcessor(const FloatColor& color,
-                                                 const string& frame_id,
+                                                 const std::string& frame_id,
                                                  PointsProcessor* const next)
     : color_(color), frame_id_(frame_id), next_(next) {}
 

cartographer/io/coloring_points_processor.h

@@ -31,7 +31,7 @@ class ColoringPointsProcessor : public PointsProcessor {
  public:
   constexpr static const char* kConfigurationFileActionName = "color_points";
 
-  ColoringPointsProcessor(const FloatColor& color, const string& frame_id,
+  ColoringPointsProcessor(const FloatColor& color, const std::string& frame_id,
                           PointsProcessor* next);
 
   static std::unique_ptr<ColoringPointsProcessor> FromDictionary(
@@ -47,7 +47,7 @@ class ColoringPointsProcessor : public PointsProcessor {
 
  private:
   const FloatColor color_;
-  const string frame_id_;
+  const std::string frame_id_;
   PointsProcessor* const next_;
 };
 

cartographer/io/file_writer.cc

@@ -19,7 +19,7 @@
 namespace cartographer {
 namespace io {
 
-StreamFileWriter::StreamFileWriter(const string& filename)
+StreamFileWriter::StreamFileWriter(const std::string& filename)
     : filename_(filename), out_(filename, std::ios::out | std::ios::binary) {}
 
 StreamFileWriter::~StreamFileWriter() {}
@@ -49,7 +49,7 @@ bool StreamFileWriter::WriteHeader(const char* const data, const size_t len) {
   return Write(data, len);
 }
 
-string StreamFileWriter::GetFilename() { return filename_; }
+std::string StreamFileWriter::GetFilename() { return filename_; }
 
 }  // namespace io
 }  // namespace cartographer

cartographer/io/file_writer.h

@@ -42,7 +42,7 @@ class FileWriter {
 
   virtual bool Write(const char* data, size_t len) = 0;
   virtual bool Close() = 0;
-  virtual string GetFilename() = 0;
+  virtual std::string GetFilename() = 0;
 };
 
 // An Implementation of file using std::ofstream.
@@ -50,20 +50,20 @@ class StreamFileWriter : public FileWriter {
  public:
   ~StreamFileWriter() override;
 
-  StreamFileWriter(const string& filename);
+  StreamFileWriter(const std::string& filename);
 
   bool Write(const char* data, size_t len) override;
   bool WriteHeader(const char* data, size_t len) override;
   bool Close() override;
-  string GetFilename() override;
+  std::string GetFilename() override;
 
  private:
-  const string filename_;
+  const std::string filename_;
   std::ofstream out_;
 };
 
 using FileWriterFactory =
-    std::function<std::unique_ptr<FileWriter>(const string& filename)>;
+    std::function<std::unique_ptr<FileWriter>(const std::string& filename)>;
 
 }  // namespace io
 }  // namespace cartographer

cartographer/io/frame_id_filtering_points_processor.cc

@@ -27,7 +27,7 @@ namespace io {
 std::unique_ptr<FrameIdFilteringPointsProcessor>
 FrameIdFilteringPointsProcessor::FromDictionary(
     common::LuaParameterDictionary* dictionary, PointsProcessor* next) {
-  std::vector<string> keep_frames, drop_frames;
+  std::vector<std::string> keep_frames, drop_frames;
   if (dictionary->HasKey("keep_frames")) {
     keep_frames =
         dictionary->GetDictionary("keep_frames")->GetArrayValuesAsStrings();
@@ -37,13 +37,15 @@ FrameIdFilteringPointsProcessor::FromDictionary(
         dictionary->GetDictionary("drop_frames")->GetArrayValuesAsStrings();
   }
   return common::make_unique<FrameIdFilteringPointsProcessor>(
-      std::unordered_set<string>(keep_frames.begin(), keep_frames.end()),
+      std::unordered_set<std::string>(keep_frames.begin(), keep_frames.end()),
-      std::unordered_set<string>(drop_frames.begin(), drop_frames.end()), next);
+      std::unordered_set<std::string>(drop_frames.begin(), drop_frames.end()),
+      next);
 }
 
 FrameIdFilteringPointsProcessor::FrameIdFilteringPointsProcessor(
-    const std::unordered_set<string>& keep_frame_ids,
+    const std::unordered_set<std::string>& keep_frame_ids,
-    const std::unordered_set<string>& drop_frame_ids, PointsProcessor* next)
+    const std::unordered_set<std::string>& drop_frame_ids,
+    PointsProcessor* next)
     : keep_frame_ids_(keep_frame_ids),
       drop_frame_ids_(drop_frame_ids),
       next_(next) {

cartographer/io/frame_id_filtering_points_processor.h

@@ -32,8 +32,9 @@ class FrameIdFilteringPointsProcessor : public PointsProcessor {
  public:
   constexpr static const char* kConfigurationFileActionName = "frame_id_filter";
   FrameIdFilteringPointsProcessor(
-      const std::unordered_set<string>& keep_frame_ids,
+      const std::unordered_set<std::string>& keep_frame_ids,
-      const std::unordered_set<string>& drop_frame_ids, PointsProcessor* next);
+      const std::unordered_set<std::string>& drop_frame_ids,
+      PointsProcessor* next);
   static std::unique_ptr<FrameIdFilteringPointsProcessor> FromDictionary(
       common::LuaParameterDictionary* dictionary, PointsProcessor* next);
   ~FrameIdFilteringPointsProcessor() override {}
@@ -47,8 +48,8 @@ class FrameIdFilteringPointsProcessor : public PointsProcessor {
   FlushResult Flush() override;
 
  private:
-  const std::unordered_set<string> keep_frame_ids_;
+  const std::unordered_set<std::string> keep_frame_ids_;
-  const std::unordered_set<string> drop_frame_ids_;
+  const std::unordered_set<std::string> drop_frame_ids_;
   PointsProcessor* const next_;
 };
 

cartographer/io/hybrid_grid_points_processor.cc

@@ -47,7 +47,7 @@ void HybridGridPointsProcessor::Process(std::unique_ptr<PointsBatch> batch) {
 PointsProcessor::FlushResult HybridGridPointsProcessor::Flush() {
   const mapping_3d::proto::HybridGrid hybrid_grid_proto =
       hybrid_grid_.ToProto();
-  string serialized;
+  std::string serialized;
   hybrid_grid_proto.SerializeToString(&serialized);
   file_writer_->Write(serialized.data(), serialized.size());
   CHECK(file_writer_->Close());

cartographer/io/intensity_to_color_points_processor.cc

@@ -28,7 +28,7 @@ std::unique_ptr<IntensityToColorPointsProcessor>
 IntensityToColorPointsProcessor::FromDictionary(
     common::LuaParameterDictionary* const dictionary,
     PointsProcessor* const next) {
-  const string frame_id =
+  const std::string frame_id =
       dictionary->HasKey("frame_id") ? dictionary->GetString("frame_id") : "";
   const float min_intensity = dictionary->GetDouble("min_intensity");
   const float max_intensity = dictionary->GetDouble("max_intensity");
@@ -38,7 +38,7 @@ IntensityToColorPointsProcessor::FromDictionary(
 
 IntensityToColorPointsProcessor::IntensityToColorPointsProcessor(
     const float min_intensity, const float max_intensity,
-    const string& frame_id, PointsProcessor* const next)
+    const std::string& frame_id, PointsProcessor* const next)
     : min_intensity_(min_intensity),
       max_intensity_(max_intensity),
       frame_id_(frame_id),

cartographer/io/intensity_to_color_points_processor.h

@@ -35,7 +35,7 @@ class IntensityToColorPointsProcessor : public PointsProcessor {
   // with this value for each point that comes from the sensor with 'frame_id'.
   // If 'frame_id' is empty, this applies to all points.
   IntensityToColorPointsProcessor(float min_intensity, float max_intensity,
-                                  const string& frame_id,
+                                  const std::string& frame_id,
                                   PointsProcessor* next);
 
   static std::unique_ptr<IntensityToColorPointsProcessor> FromDictionary(
@@ -54,7 +54,7 @@ class IntensityToColorPointsProcessor : public PointsProcessor {
  private:
   const float min_intensity_;
   const float max_intensity_;
-  const string frame_id_;
+  const std::string frame_id_;
   PointsProcessor* const next_;
 };
 

cartographer/io/pcd_writing_points_processor.cc

@@ -34,10 +34,10 @@ namespace {
 // 'output_file'.
 void WriteBinaryPcdHeader(const bool has_color, const int64 num_points,
                           FileWriter* const file_writer) {
-  string color_header_field = !has_color ? "" : " rgb";
+  std::string color_header_field = !has_color ? "" : " rgb";
-  string color_header_type = !has_color ? "" : " U";
+  std::string color_header_type = !has_color ? "" : " U";
-  string color_header_size = !has_color ? "" : " 4";
+  std::string color_header_size = !has_color ? "" : " 4";
-  string color_header_count = !has_color ? "" : " 1";
+  std::string color_header_count = !has_color ? "" : " 1";
 
   std::ostringstream stream;
   stream << "# generated by Cartographer\n"
@@ -52,7 +52,7 @@ void WriteBinaryPcdHeader(const bool has_color, const int64 num_points,
          << "POINTS " << std::setw(15) << std::setfill('0') << num_points
          << "\n"
          << "DATA binary\n";
-  const string out = stream.str();
+  const std::string out = stream.str();
   file_writer->WriteHeader(out.data(), out.size());
 }
 

cartographer/io/ply_writing_points_processor.cc

@@ -34,7 +34,7 @@ namespace {
 // 'output_file'.
 void WriteBinaryPlyHeader(const bool has_color, const int64 num_points,
                           FileWriter* const file_writer) {
-  string color_header = !has_color ? ""
+  std::string color_header = !has_color ? ""
                                         : "property uchar red\n"
                                           "property uchar green\n"
                                           "property uchar blue\n";
@@ -48,7 +48,7 @@ void WriteBinaryPlyHeader(const bool has_color, const int64 num_points,
          << "property float y\n"
          << "property float z\n"
          << color_header << "end_header\n";
-  const string out = stream.str();
+  const std::string out = stream.str();
   CHECK(file_writer->WriteHeader(out.data(), out.size()));
 }
 

cartographer/io/points_batch.h

@@ -46,7 +46,7 @@ struct PointsBatch {
 
   // Sensor that generated this data's 'frame_id' or empty if this information
   // is unknown.
-  string frame_id;
+  std::string frame_id;
 
   // Trajectory ID that produced this point.
   int trajectory_id;

cartographer/io/points_processor_pipeline_builder.cc

@@ -125,7 +125,7 @@ PointsProcessorPipelineBuilder::CreatePipeline(
 
   // We construct the pipeline starting at the back.
   for (auto it = configurations.rbegin(); it != configurations.rend(); it++) {
-    const string action = (*it)->GetString("action");
+    const std::string action = (*it)->GetString("action");
     auto factory_it = factories_.find(action);
     CHECK(factory_it != factories_.end())
         << "Unknown action '" << action

cartographer/io/points_processor_pipeline_builder_test.cc

@@ -29,7 +29,7 @@ namespace {
 TEST(PointsProcessorPipelineBuilderTest, RegisterBuiltInPointsProcessors) {
   PointsProcessorPipelineBuilder builder;
   FileWriterFactory dummy_factory =
-      [](const string& filename) -> std::unique_ptr<FileWriter> {
+      [](const std::string& filename) -> std::unique_ptr<FileWriter> {
     return nullptr;
   };
   RegisterBuiltInPointsProcessors({}, dummy_factory, &builder);

cartographer/io/proto_stream.cc

@@ -42,15 +42,15 @@ bool ReadSizeAsLittleEndian(std::istream* in, uint64* size) {
 
 }  // namespace
 
-ProtoStreamWriter::ProtoStreamWriter(const string& filename)
+ProtoStreamWriter::ProtoStreamWriter(const std::string& filename)
     : out_(filename, std::ios::out | std::ios::binary) {
   WriteSizeAsLittleEndian(kMagic, &out_);
 }
 
 ProtoStreamWriter::~ProtoStreamWriter() {}
 
-void ProtoStreamWriter::Write(const string& uncompressed_data) {
+void ProtoStreamWriter::Write(const std::string& uncompressed_data) {
-  string compressed_data;
+  std::string compressed_data;
   common::FastGzipString(uncompressed_data, &compressed_data);
   WriteSizeAsLittleEndian(compressed_data.size(), &out_);
   out_.write(compressed_data.data(), compressed_data.size());
@@ -61,7 +61,7 @@ bool ProtoStreamWriter::Close() {
   return !out_.fail();
 }
 
-ProtoStreamReader::ProtoStreamReader(const string& filename)
+ProtoStreamReader::ProtoStreamReader(const std::string& filename)
     : in_(filename, std::ios::in | std::ios::binary) {
   uint64 magic;
   if (!ReadSizeAsLittleEndian(&in_, &magic) || magic != kMagic) {
@@ -71,12 +71,12 @@ ProtoStreamReader::ProtoStreamReader(const string& filename)
 
 ProtoStreamReader::~ProtoStreamReader() {}
 
-bool ProtoStreamReader::Read(string* decompressed_data) {
+bool ProtoStreamReader::Read(std::string* decompressed_data) {
   uint64 compressed_size;
   if (!ReadSizeAsLittleEndian(&in_, &compressed_size)) {
     return false;
   }
-  string compressed_data(compressed_size, '\0');
+  std::string compressed_data(compressed_size, '\0');
   if (!in_.read(&compressed_data.front(), compressed_size)) {
     return false;
   }

cartographer/io/proto_stream.h

@@ -32,7 +32,7 @@ namespace io {
 // compression performance? Should we use LZ4?
 class ProtoStreamWriter {
  public:
-  ProtoStreamWriter(const string& filename);
+  ProtoStreamWriter(const std::string& filename);
   ~ProtoStreamWriter();
 
   ProtoStreamWriter(const ProtoStreamWriter&) = delete;
@@ -41,7 +41,7 @@ class ProtoStreamWriter {
   // Serializes, compressed and writes the 'proto' to the file.
   template <typename MessageType>
   void WriteProto(const MessageType& proto) {
-    string uncompressed_data;
+    std::string uncompressed_data;
     proto.SerializeToString(&uncompressed_data);
     Write(uncompressed_data);
   }
@@ -50,7 +50,7 @@ class ProtoStreamWriter {
   bool Close();
 
  private:
-  void Write(const string& uncompressed_data);
+  void Write(const std::string& uncompressed_data);
 
   std::ofstream out_;
 };
@@ -58,7 +58,7 @@ class ProtoStreamWriter {
 // A reader of the format produced by ProtoStreamWriter.
 class ProtoStreamReader {
  public:
-  ProtoStreamReader(const string& filename);
+  ProtoStreamReader(const std::string& filename);
   ~ProtoStreamReader();
 
   ProtoStreamReader(const ProtoStreamReader&) = delete;
@@ -66,7 +66,7 @@ class ProtoStreamReader {
 
   template <typename MessageType>
   bool ReadProto(MessageType* proto) {
-    string decompressed_data;
+    std::string decompressed_data;
     return Read(&decompressed_data) &&
            proto->ParseFromString(decompressed_data);
   }
@@ -74,7 +74,7 @@ class ProtoStreamReader {
   bool eof() const;
 
  private:
-  bool Read(string* decompressed_data);
+  bool Read(std::string* decompressed_data);
 
   std::ifstream in_;
 };

cartographer/io/proto_stream_test.cc

@@ -32,18 +32,18 @@ namespace {
 class ProtoStreamTest : public ::testing::Test {
  protected:
   void SetUp() override {
-    const string tmpdir = P_tmpdir;
+    const std::string tmpdir = P_tmpdir;
     test_directory_ = tmpdir + "/proto_stream_test_XXXXXX";
     ASSERT_NE(mkdtemp(&test_directory_[0]), nullptr) << strerror(errno);
   }
 
   void TearDown() override { remove(test_directory_.c_str()); }
 
-  string test_directory_;
+  std::string test_directory_;
 };
 
 TEST_F(ProtoStreamTest, WriteAndReadBack) {
-  const string test_file = test_directory_ + "/test_trajectory.pbstream";
+  const std::string test_file = test_directory_ + "/test_trajectory.pbstream";
   {
     ProtoStreamWriter writer(test_file);
     for (int i = 0; i != 10; ++i) {

cartographer/io/xray_points_processor.cc

@@ -98,7 +98,8 @@ bool ContainedIn(const common::Time& time,
 XRayPointsProcessor::XRayPointsProcessor(
     const double voxel_size, const transform::Rigid3f& transform,
     const std::vector<mapping::Floor>& floors,
-    const DrawTrajectories& draw_trajectories, const string& output_filename,
+    const DrawTrajectories& draw_trajectories,
+    const std::string& output_filename,
     const std::vector<mapping::proto::Trajectory>& trajectories,
     FileWriterFactory file_writer_factory, PointsProcessor* const next)
     : draw_trajectories_(draw_trajectories),

cartographer/io/xray_points_processor.h

@@ -40,7 +40,8 @@ class XRayPointsProcessor : public PointsProcessor {
   XRayPointsProcessor(
       double voxel_size, const transform::Rigid3f& transform,
       const std::vector<mapping::Floor>& floors,
-      const DrawTrajectories& draw_trajectories, const string& output_filename,
+      const DrawTrajectories& draw_trajectories,
+      const std::string& output_filename,
       const std::vector<mapping::proto::Trajectory>& trajectories,
       FileWriterFactory file_writer_factory, PointsProcessor* next);
 
@@ -81,7 +82,7 @@ class XRayPointsProcessor : public PointsProcessor {
   // If empty, we do not separate into floors.
   std::vector<mapping::Floor> floors_;
 
-  const string output_filename_;
+  const std::string output_filename_;
   const transform::Rigid3f transform_;
 
   // Only has one entry if we do not separate into floors.

cartographer/io/xyz_writing_points_processor.cc

@@ -15,7 +15,7 @@ void WriteXyzPoint(const Eigen::Vector3f& point,
   std::ostringstream stream;
   stream << std::setprecision(6);
   stream << point.x() << " " << point.y() << " " << point.z() << "\n";
-  const string out = stream.str();
+  const std::string out = stream.str();
   CHECK(file_writer->Write(out.data(), out.size()));
 }
 

cartographer/mapping/collated_trajectory_builder.cc

@@ -30,7 +30,7 @@ constexpr double kSensorDataRatesLoggingPeriodSeconds = 15.;
 
 CollatedTrajectoryBuilder::CollatedTrajectoryBuilder(
     sensor::Collator* const sensor_collator, const int trajectory_id,
-    const std::unordered_set<string>& expected_sensor_ids,
+    const std::unordered_set<std::string>& expected_sensor_ids,
     std::unique_ptr<GlobalTrajectoryBuilderInterface>
         wrapped_trajectory_builder)
     : sensor_collator_(sensor_collator),
@@ -39,7 +39,7 @@ CollatedTrajectoryBuilder::CollatedTrajectoryBuilder(
       last_logging_time_(std::chrono::steady_clock::now()) {
   sensor_collator_->AddTrajectory(
       trajectory_id, expected_sensor_ids,
-      [this](const string& sensor_id, std::unique_ptr<sensor::Data> data) {
+      [this](const std::string& sensor_id, std::unique_ptr<sensor::Data> data) {
         HandleCollatedSensorData(sensor_id, std::move(data));
       });
 }
@@ -51,12 +51,12 @@ const PoseEstimate& CollatedTrajectoryBuilder::pose_estimate() const {
 }
 
 void CollatedTrajectoryBuilder::AddSensorData(
-    const string& sensor_id, std::unique_ptr<sensor::Data> data) {
+    const std::string& sensor_id, std::unique_ptr<sensor::Data> data) {
   sensor_collator_->AddSensorData(trajectory_id_, sensor_id, std::move(data));
 }
 
 void CollatedTrajectoryBuilder::HandleCollatedSensorData(
-    const string& sensor_id, std::unique_ptr<sensor::Data> data) {
+    const std::string& sensor_id, std::unique_ptr<sensor::Data> data) {
   auto it = rate_timers_.find(sensor_id);
   if (it == rate_timers_.end()) {
     it = rate_timers_

cartographer/mapping/collated_trajectory_builder.h

@@ -40,7 +40,7 @@ class CollatedTrajectoryBuilder : public TrajectoryBuilder {
  public:
   CollatedTrajectoryBuilder(
       sensor::Collator* sensor_collator, int trajectory_id,
-      const std::unordered_set<string>& expected_sensor_ids,
+      const std::unordered_set<std::string>& expected_sensor_ids,
       std::unique_ptr<GlobalTrajectoryBuilderInterface>
           wrapped_trajectory_builder);
   ~CollatedTrajectoryBuilder() override;
@@ -51,11 +51,11 @@ class CollatedTrajectoryBuilder : public TrajectoryBuilder {
 
   const PoseEstimate& pose_estimate() const override;
 
-  void AddSensorData(const string& sensor_id,
+  void AddSensorData(const std::string& sensor_id,
                      std::unique_ptr<sensor::Data> data) override;
 
  private:
-  void HandleCollatedSensorData(const string& sensor_id,
+  void HandleCollatedSensorData(const std::string& sensor_id,
                                 std::unique_ptr<sensor::Data> data);
 
   sensor::Collator* const sensor_collator_;
@@ -64,7 +64,7 @@ class CollatedTrajectoryBuilder : public TrajectoryBuilder {
 
   // Time at which we last logged the rates of incoming sensor data.
   std::chrono::steady_clock::time_point last_logging_time_;
-  std::map<string, common::RateTimer<>> rate_timers_;
+  std::map<std::string, common::RateTimer<>> rate_timers_;
 };
 
 }  // namespace mapping

cartographer/mapping/map_builder.cc

@@ -74,7 +74,7 @@ MapBuilder::MapBuilder(
 MapBuilder::~MapBuilder() {}
 
 int MapBuilder::AddTrajectoryBuilder(
-    const std::unordered_set<string>& expected_sensor_ids,
+    const std::unordered_set<std::string>& expected_sensor_ids,
     const proto::TrajectoryBuilderOptions& trajectory_options) {
   const int trajectory_id = trajectory_builders_.size();
   if (options_.use_trajectory_builder_3d()) {
@@ -138,7 +138,8 @@ int MapBuilder::GetBlockingTrajectoryId() const {
   return sensor_collator_.GetBlockingTrajectoryId();
 }
 
-string MapBuilder::SubmapToProto(const mapping::SubmapId& submap_id,
+std::string MapBuilder::SubmapToProto(
+    const mapping::SubmapId& submap_id,
     proto::SubmapQuery::Response* const response) {
   if (submap_id.trajectory_id < 0 ||
       submap_id.trajectory_id >= num_trajectory_builders()) {

cartographer/mapping/map_builder.h

@@ -61,7 +61,7 @@ class MapBuilder {
 
   // Creates a new trajectory builder and returns its index.
   int AddTrajectoryBuilder(
-      const std::unordered_set<string>& expected_sensor_ids,
+      const std::unordered_set<std::string>& expected_sensor_ids,
       const proto::TrajectoryBuilderOptions& trajectory_options);
 
   // Creates a new trajectory and returns its index. Querying the trajectory
@@ -84,7 +84,7 @@ class MapBuilder {
 
   // Fills the SubmapQuery::Response corresponding to 'submap_id'. Returns an
   // error string on failure, or an empty string on success.
-  string SubmapToProto(const SubmapId& submap_id,
+  std::string SubmapToProto(const SubmapId& submap_id,
                             proto::SubmapQuery::Response* response);
 
   // Serializes the current state to a proto stream.

cartographer/mapping/trajectory_builder.h

@@ -50,10 +50,10 @@ class TrajectoryBuilder {
 
   virtual const PoseEstimate& pose_estimate() const = 0;
 
-  virtual void AddSensorData(const string& sensor_id,
+  virtual void AddSensorData(const std::string& sensor_id,
                              std::unique_ptr<sensor::Data> data) = 0;
 
-  void AddRangefinderData(const string& sensor_id, common::Time time,
+  void AddRangefinderData(const std::string& sensor_id, common::Time time,
                           const Eigen::Vector3f& origin,
                           const sensor::TimedPointCloud& ranges) {
     AddSensorData(sensor_id,
@@ -61,20 +61,20 @@ class TrajectoryBuilder {
                       time, origin, ranges));
   }
 
-  void AddImuData(const string& sensor_id, common::Time time,
+  void AddImuData(const std::string& sensor_id, common::Time time,
                   const Eigen::Vector3d& linear_acceleration,
                   const Eigen::Vector3d& angular_velocity) {
     AddSensorData(sensor_id, sensor::MakeDispatchable(sensor::ImuData{
                                  time, linear_acceleration, angular_velocity}));
   }
 
-  void AddOdometerData(const string& sensor_id, common::Time time,
+  void AddOdometerData(const std::string& sensor_id, common::Time time,
                        const transform::Rigid3d& odometer_pose) {
     AddSensorData(sensor_id, sensor::MakeDispatchable(
                                  sensor::OdometryData{time, odometer_pose}));
   }
 
-  void AddFixedFramePoseData(const string& sensor_id, common::Time time,
+  void AddFixedFramePoseData(const std::string& sensor_id, common::Time time,
                              const transform::Rigid3d& fixed_frame_pose) {
     AddSensorData(sensor_id,
                   sensor::MakeDispatchable(

cartographer/mapping_2d/submaps.cc

@@ -91,7 +91,7 @@ void Submap::ToResponseProto(
   CellLimits limits;
   probability_grid_.ComputeCroppedLimits(&offset, &limits);
 
-  string cells;
+  std::string cells;
   for (const Eigen::Array2i& xy_index : XYIndexRangeIterator(limits)) {
     if (probability_grid_.IsKnown(xy_index + offset)) {
       // We would like to add 'delta' but this is not possible using a value and

cartographer/mapping_3d/scan_matching/ceres_scan_matcher.cc

@@ -40,7 +40,8 @@ proto::CeresScanMatcherOptions CreateCeresScanMatcherOptions(
     common::LuaParameterDictionary* const parameter_dictionary) {
   proto::CeresScanMatcherOptions options;
   for (int i = 0;; ++i) {
-    const string lua_identifier = "occupied_space_weight_" + std::to_string(i);
+    const std::string lua_identifier =
+        "occupied_space_weight_" + std::to_string(i);
     if (!parameter_dictionary->HasKey(lua_identifier)) {
       break;
     }

cartographer/mapping_3d/submaps.cc

@@ -113,9 +113,9 @@ std::vector<Eigen::Array4i> ExtractVoxelData(
 
 // Builds texture data containing interleaved value and alpha for the
 // visualization from 'accumulated_pixel_data'.
-string ComputePixelValues(
+std::string ComputePixelValues(
     const std::vector<PixelData>& accumulated_pixel_data) {
-  string cell_data;
+  std::string cell_data;
   cell_data.reserve(2 * accumulated_pixel_data.size());
   constexpr float kMinZDifference = 3.f;
   constexpr float kFreeSpaceWeight = 0.15f;
@@ -168,7 +168,7 @@ void AddToTextureProto(
 
   const std::vector<PixelData> accumulated_pixel_data = AccumulatePixelData(
       width, height, min_index, max_index, voxel_indices_and_probabilities);
-  const string cell_data = ComputePixelValues(accumulated_pixel_data);
+  const std::string cell_data = ComputePixelValues(accumulated_pixel_data);
 
   common::FastGzipString(cell_data, texture->mutable_cells());
   *texture->mutable_slice_pose() = transform::ToProto(

cartographer/sensor/collator.cc

@@ -21,7 +21,7 @@ namespace sensor {
 
 void Collator::AddTrajectory(
     const int trajectory_id,
-    const std::unordered_set<string>& expected_sensor_ids,
+    const std::unordered_set<std::string>& expected_sensor_ids,
     const Callback& callback) {
   for (const auto& sensor_id : expected_sensor_ids) {
     const auto queue_key = QueueKey{trajectory_id, sensor_id};
@@ -39,7 +39,8 @@ void Collator::FinishTrajectory(const int trajectory_id) {
   }
 }
 
-void Collator::AddSensorData(const int trajectory_id, const string& sensor_id,
+void Collator::AddSensorData(const int trajectory_id,
+                             const std::string& sensor_id,
                              std::unique_ptr<Data> data) {
   queue_.Add(QueueKey{trajectory_id, sensor_id}, std::move(data));
 }

cartographer/sensor/collator.h

@@ -31,7 +31,8 @@ namespace sensor {
 
 class Collator {
  public:
-  using Callback = std::function<void(const string&, std::unique_ptr<Data>)>;
+  using Callback =
+      std::function<void(const std::string&, std::unique_ptr<Data>)>;
 
   Collator() {}
 
@@ -41,7 +42,7 @@ class Collator {
   // Adds a trajectory to produce sorted sensor output for. Calls 'callback'
   // for each collated sensor data.
   void AddTrajectory(int trajectory_id,
-                     const std::unordered_set<string>& expected_sensor_ids,
+                     const std::unordered_set<std::string>& expected_sensor_ids,
                      const Callback& callback);
 
   // Marks 'trajectory_id' as finished.
@@ -50,7 +51,7 @@ class Collator {
   // Adds 'data' for 'trajectory_id' to be collated. 'data' must contain valid
   // sensor data. Sensor packets with matching 'sensor_id' must be added in time
   // order.
-  void AddSensorData(int trajectory_id, const string& sensor_id,
+  void AddSensorData(int trajectory_id, const std::string& sensor_id,
                      std::unique_ptr<Data> data);
 
   // Dispatches all queued sensor packets. May only be called once.

cartographer/sensor/collator_test.cc

@@ -30,7 +30,7 @@ namespace sensor {
 namespace {
 
 TEST(Collator, Ordering) {
-  const std::array<string, 4> kSensorId = {
+  const std::array<std::string, 4> kSensorId = {
       {"horizontal_rangefinder", "vertical_rangefinder", "imu", "odometry"}};
   DispatchableRangefinderData zero(common::FromUniversal(0),
                                    Eigen::Vector3f::Zero(), {});
@@ -46,11 +46,11 @@ TEST(Collator, Ordering) {
   OdometryData sixth{common::FromUniversal(600),
                      transform::Rigid3d::Identity()};
 
-  std::vector<std::pair<string, common::Time>> received;
+  std::vector<std::pair<std::string, common::Time>> received;
   Collator collator;
   collator.AddTrajectory(
-      0, std::unordered_set<string>(kSensorId.begin(), kSensorId.end()),
+      0, std::unordered_set<std::string>(kSensorId.begin(), kSensorId.end()),
-      [&received](const string& sensor_id, std::unique_ptr<Data> data) {
+      [&received](const std::string& sensor_id, std::unique_ptr<Data> data) {
         received.push_back(std::make_pair(sensor_id, data->GetTime()));
       });
 

cartographer/sensor/compressed_point_cloud_test.cc

@@ -41,7 +41,7 @@ constexpr float kPrecision = 0.001f;
 
 // Matcher for 3-d vectors w.r.t. to the target precision.
 MATCHER_P(ApproximatelyEquals, expected,
-          string("is equal to ") + PrintToString(expected)) {
+          std::string("is equal to ") + PrintToString(expected)) {
   return (arg - expected).isZero(kPrecision);
 }
 

cartographer/sensor/landmark_data.h

@@ -30,7 +30,7 @@ namespace cartographer {
 namespace sensor {
 
 struct Landmark {
-  string id;
+  std::string id;
   transform::Rigid3d transform;
   double translation_weight;
   double rotation_weight;

cartographer/sensor/ordered_multi_queue.h

@@ -33,7 +33,7 @@ namespace sensor {
 
 struct QueueKey {
   int trajectory_id;
-  string sensor_id;
+  std::string sensor_id;
 
   bool operator<(const QueueKey& other) const {
     return std::forward_as_tuple(trajectory_id, sensor_id) <

cartographer/transform/rigid_transform.h

@@ -76,8 +76,8 @@ class Rigid2 {
     return Rigid2(translation, rotation);
   }
 
-  string DebugString() const {
+  std::string DebugString() const {
-    string out;
+    std::string out;
     out.append("{ t: [");
     out.append(std::to_string(translation().x()));
     out.append(", ");
@@ -161,8 +161,8 @@ class Rigid3 {
     return Rigid3(translation, rotation);
   }
 
-  string DebugString() const {
+  std::string DebugString() const {
-    string out;
+    std::string out;
     out.append("{ t: [");
     out.append(std::to_string(translation().x()));
     out.append(", ");

cartographer/transform/rigid_transform_test_helpers.h

@@ -40,7 +40,7 @@ Eigen::Transform<T, 3, Eigen::Affine> ToEigen(const Rigid3<T>& rigid3) {
 }
 
 MATCHER_P2(IsNearly, rigid, epsilon,
-           string(string(negation ? "isn't" : "is", " nearly ") +
+           std::string(std::string(negation ? "isn't" : "is", " nearly ") +
                        rigid.DebugString())) {
   return ToEigen(arg).isApprox(ToEigen(rigid), epsilon);
 }