change GetTrainnigScore to non-const.

include/LightGBM/boosting.h

@@ -64,7 +64,7 @@ public:
   * \param out_len length of returned score
   * \return training score
   */
-  virtual const score_t* GetTrainingScore(data_size_t* out_len) const = 0;
+  virtual const score_t* GetTrainingScore(data_size_t* out_len) = 0;
 
   /*!
   * \brief Get prediction result at data_idx data

src/boosting/gbdt.cpp

@@ -294,7 +294,7 @@ std::vector<double> GBDT::GetEvalAt(int data_idx) const {
 }
 
 /*! \brief Get training scores result */
-const score_t* GBDT::GetTrainingScore(data_size_t* out_len) const {
+const score_t* GBDT::GetTrainingScore(data_size_t* out_len) {
   *out_len = train_score_updater_->num_data() * num_class_;
   return train_score_updater_->score();
 }

src/boosting/gbdt.h

@@ -62,7 +62,7 @@ public:
   * \param out_len lenght of returned score
   * \return training score
   */
-  const score_t* GetTrainingScore(data_size_t* out_len) const override;
+  const score_t* GetTrainingScore(data_size_t* out_len) override;
 
   /*!
   * \brief Get prediction result at data_idx data

src/c_api.cpp

@@ -127,8 +127,11 @@ public:
   void SaveModelToFile(int num_used_model, const char* filename) {
     boosting_->SaveModelToFile(num_used_model, true, filename);
   }
+  
   const Boosting* GetBoosting() const { return boosting_; }
 
+  const float* GetTrainingScore(int* out_len) const { return boosting_->GetTrainingScore(out_len); }
+
   const inline int NumberOfClasses() const { return boosting_->NumberOfClasses(); }
 
 private:
@@ -478,9 +481,8 @@ DllExport int LGBM_BoosterGetScore(BoosterHandle handle,
   const float** out_result) {
 
   Booster* ref_booster = reinterpret_cast<Booster*>(handle);
-  auto boosting = ref_booster->GetBoosting();
   int len = 0;
-  *out_result = boosting->GetTrainingScore(&len);
+  *out_result = ref_booster->GetTrainingScore(&len);
   *out_len = static_cast<int64_t>(len);
 
   return 0;