Fix user locale settings (#2980)

This reverts commit 6b68967d (#2891) and fixes #2979.

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

@@ -13,7 +13,6 @@
 #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>
@@ -1237,7 +1236,6 @@ 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();
@@ -1249,7 +1247,6 @@ 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();
@@ -1674,7 +1671,6 @@ 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();
@@ -1687,7 +1683,6 @@ 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;
@@ -1704,7 +1699,6 @@ 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;