Fix Booster read/write locale dependency (#2891)

* Fix Booster read/write locale dependency

* Address review comments

* Move LocaleContext.h->locale_context.h
Co-authored-by: alberto.ferreira <alberto.ferreira@feedzai.com>

include/LightGBM/utils/locale_context.h

+/*!
+ * Copyright (c) 2020 Microsoft Corporation. All rights reserved.
+ * Licensed under the MIT License. See LICENSE file in the project root for license information.
+ */
+#ifndef LIGHTGBM_LOCALE_CONTEXT_H_
+#define LIGHTGBM_LOCALE_CONTEXT_H_
+
+#include <clocale>
+#include <locale>
+
+/*!
+ * Class to override the program global locale during this object lifetime.
+ * After the object is destroyed, the locale is returned to its original state.
+ *
+ * @warn This is not thread-safe.
+ */
+class LocaleContext {
+ public:
+  /*!
+   * Override the current program global locale during this object lifetime.
+   *
+   * @param target_locale override the locale to this locale setting.
+   * @warn This is not thread-safe.
+   * @note This doesn't override cout, cerr, etc.
+   */
+  explicit LocaleContext(const char* target_locale = "C") {
+    std::locale::global(std::locale(target_locale));
+  }
+
+  /*!
+   * Restores the old global locale.
+   */
+  ~LocaleContext() {
+    std::locale::global(_saved_global_locale);
+  }
+ private:
+  std::locale _saved_global_locale;  //!< Stores global locale at initialization.
+};
+
+#endif  // LIGHTGBM_LOCALE_CONTEXT_H_

src/c_api.cpp

@@ -13,6 +13,7 @@
 #include <LightGBM/objective_function.h>
 #include <LightGBM/prediction_early_stop.h>
 #include <LightGBM/utils/common.h>
+#include <LightGBM/utils/locale_context.h>
 #include <LightGBM/utils/log.h>
 #include <LightGBM/utils/openmp_wrapper.h>
 #include <LightGBM/utils/random.h>
@@ -1210,6 +1211,7 @@ int LGBM_BoosterCreateFromModelfile(
   int* out_num_iterations,
   BoosterHandle* out) {
   API_BEGIN();
+  LocaleContext withLocaleContext("C");
   auto ret = std::unique_ptr<Booster>(new Booster(filename));
   *out_num_iterations = ret->GetBoosting()->GetCurrentIteration();
   *out = ret.release();
@@ -1221,6 +1223,7 @@ int LGBM_BoosterLoadModelFromString(
   int* out_num_iterations,
   BoosterHandle* out) {
   API_BEGIN();
+  LocaleContext withLocaleContext("C");
   auto ret = std::unique_ptr<Booster>(new Booster(nullptr));
   ret->LoadModelFromString(model_str);
   *out_num_iterations = ret->GetBoosting()->GetCurrentIteration();
@@ -1635,6 +1638,7 @@ int LGBM_BoosterSaveModel(BoosterHandle handle,
                           int num_iteration,
                           const char* filename) {
   API_BEGIN();
+  LocaleContext withLocaleContext("C");
   Booster* ref_booster = reinterpret_cast<Booster*>(handle);
   ref_booster->SaveModelToFile(start_iteration, num_iteration, filename);
   API_END();
@@ -1647,6 +1651,7 @@ int LGBM_BoosterSaveModelToString(BoosterHandle handle,
                                   int64_t* out_len,
                                   char* out_str) {
   API_BEGIN();
+  LocaleContext withLocaleContext("C");
   Booster* ref_booster = reinterpret_cast<Booster*>(handle);
   std::string model = ref_booster->SaveModelToString(start_iteration, num_iteration);
   *out_len = static_cast<int64_t>(model.size()) + 1;
@@ -1663,6 +1668,7 @@ int LGBM_BoosterDumpModel(BoosterHandle handle,
                           int64_t* out_len,
                           char* out_str) {
   API_BEGIN();
+  LocaleContext withLocaleContext("C");
   Booster* ref_booster = reinterpret_cast<Booster*>(handle);
   std::string model = ref_booster->DumpModel(start_iteration, num_iteration);
   *out_len = static_cast<int64_t>(model.size()) + 1;