diff --git a/internal/ceres/callbacks.cc b/internal/ceres/callbacks.cc
index 0e0df9d..e6e0644 100644
--- a/internal/ceres/callbacks.cc
+++ b/internal/ceres/callbacks.cc
@@ -1,5 +1,5 @@
 // Ceres Solver - A fast non-linear least squares minimizer
-// Copyright 2015 Google Inc. All rights reserved.
+// Copyright 2023 Google Inc. All rights reserved.
 // http://ceres-solver.org/
 //
 // Redistribution and use in source and binary forms, with or without
@@ -30,25 +30,24 @@
 
 #include "ceres/callbacks.h"
 
+#include <algorithm>
 #include <iostream>  // NO LINT
+#include <string>
 
 #include "ceres/program.h"
 #include "ceres/stringprintf.h"
 #include "glog/logging.h"
 
-namespace ceres {
-namespace internal {
-
-using std::string;
+namespace ceres::internal {
 
 StateUpdatingCallback::StateUpdatingCallback(Program* program,
                                              double* parameters)
     : program_(program), parameters_(parameters) {}
 
-StateUpdatingCallback::~StateUpdatingCallback() {}
+StateUpdatingCallback::~StateUpdatingCallback() = default;
 
 CallbackReturnType StateUpdatingCallback::operator()(
-    const IterationSummary& summary) {
+    const IterationSummary& /*summary*/) {
   program_->StateVectorToParameterBlocks(parameters_);
   program_->CopyParameterBlockStateToUserState();
   return SOLVER_CONTINUE;
@@ -64,14 +63,12 @@
       user_parameters_(user_parameters) {}
 
 GradientProblemSolverStateUpdatingCallback::
-    ~GradientProblemSolverStateUpdatingCallback() {}
+    ~GradientProblemSolverStateUpdatingCallback() = default;
 
 CallbackReturnType GradientProblemSolverStateUpdatingCallback::operator()(
     const IterationSummary& summary) {
   if (summary.step_is_successful) {
-    std::copy(internal_parameters_,
-              internal_parameters_ + num_parameters_,
-              user_parameters_);
+    std::copy_n(internal_parameters_, num_parameters_, user_parameters_);
   }
   return SOLVER_CONTINUE;
 }
@@ -80,44 +77,42 @@
                                  const bool log_to_stdout)
     : minimizer_type(minimizer_type), log_to_stdout_(log_to_stdout) {}
 
-LoggingCallback::~LoggingCallback() {}
+LoggingCallback::~LoggingCallback() = default;
 
 CallbackReturnType LoggingCallback::operator()(
     const IterationSummary& summary) {
-  string output;
+  std::string output;
   if (minimizer_type == LINE_SEARCH) {
-    const char* kReportRowFormat =
-        "% 4d: f:% 8e d:% 3.2e g:% 3.2e h:% 3.2e "
-        "s:% 3.2e e:% 3d it:% 3.2e tt:% 3.2e";
-    output = StringPrintf(kReportRowFormat,
-                          summary.iteration,
-                          summary.cost,
-                          summary.cost_change,
-                          summary.gradient_max_norm,
-                          summary.step_norm,
-                          summary.step_size,
-                          summary.line_search_function_evaluations,
-                          summary.iteration_time_in_seconds,
-                          summary.cumulative_time_in_seconds);
+    output = StringPrintf(
+        "% 4d: f:% 8e d:% 3.2e g:% 3.2e h:% 3.2e s:% 3.2e e:% 3d it:% 3.2e "
+        "tt:% 3.2e",
+        summary.iteration,
+        summary.cost,
+        summary.cost_change,
+        summary.gradient_max_norm,
+        summary.step_norm,
+        summary.step_size,
+        summary.line_search_function_evaluations,
+        summary.iteration_time_in_seconds,
+        summary.cumulative_time_in_seconds);
   } else if (minimizer_type == TRUST_REGION) {
     // clang-format off
     if (summary.iteration == 0) {
       output = "iter      cost      cost_change  |gradient|   |step|    tr_ratio  tr_radius  ls_iter  iter_time  total_time\n";  // NOLINT
     }
-    const char* kReportRowFormat =
-        "% 4d % 8e   % 3.2e   % 3.2e  % 3.2e  % 3.2e % 3.2e     % 4d   % 3.2e   % 3.2e";  // NOLINT
-    // clang-format on
-    output += StringPrintf(kReportRowFormat,
-                           summary.iteration,
-                           summary.cost,
-                           summary.cost_change,
-                           summary.gradient_max_norm,
-                           summary.step_norm,
-                           summary.relative_decrease,
-                           summary.trust_region_radius,
-                           summary.linear_solver_iterations,
-                           summary.iteration_time_in_seconds,
-                           summary.cumulative_time_in_seconds);
+    output += StringPrintf(
+        "% 4d % 8e   % 3.2e   % 3.2e  % 3.2e  % 3.2e % 3.2e     % 4d   % 3.2e   % 3.2e",  // NOLINT
+        // clang-format on
+        summary.iteration,
+        summary.cost,
+        summary.cost_change,
+        summary.gradient_max_norm,
+        summary.step_norm,
+        summary.relative_decrease,
+        summary.trust_region_radius,
+        summary.linear_solver_iterations,
+        summary.iteration_time_in_seconds,
+        summary.cumulative_time_in_seconds);
   } else {
     LOG(FATAL) << "Unknown minimizer type.";
   }
@@ -130,5 +125,4 @@
   return SOLVER_CONTINUE;
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal