Added `SaveModelToString` and modified `SaveModelToFile` to use it. (#235)

include/LightGBM/boosting.h

@@ -147,6 +147,13 @@ public:
   */
   virtual bool SaveModelToFile(int num_iterations, const char* filename) const = 0;
 
+  /*!
+  * \brief Save model to string
+  * \param num_used_model Number of model that want to save, -1 means save all
+  * \return Non-empty string if succeeded
+  */
+  virtual std::string SaveModelToString(int num_iterations) const = 0;
+
   /*!
   * \brief Restore from a serialized string
   * \param model_str The string of model

src/boosting/gbdt.cpp

@@ -509,49 +509,58 @@ std::string GBDT::DumpModel(int num_iteration) const {
   return str_buf.str();
 }
 
-bool GBDT::SaveModelToFile(int num_iteration, const char* filename) const {
-  /*! \brief File to write models */
-  std::ofstream output_file;
-  output_file.open(filename);
+std::string GBDT::SaveModelToString(int num_iterations) const {
+    std::stringstream ss;
+
     // output model type
-  output_file << SubModelName() << std::endl;
+    ss << SubModelName() << std::endl;
     // output number of class
-  output_file << "num_class=" << num_class_ << std::endl;
+    ss << "num_class=" << num_class_ << std::endl;
     // output label index
-  output_file << "label_index=" << label_idx_ << std::endl;
+    ss << "label_index=" << label_idx_ << std::endl;
     // output max_feature_idx
-  output_file << "max_feature_idx=" << max_feature_idx_ << std::endl;
+    ss << "max_feature_idx=" << max_feature_idx_ << std::endl;
     // output objective name
     if (object_function_ != nullptr) {
-    output_file << "objective=" << object_function_->GetName() << std::endl;
+      ss << "objective=" << object_function_->GetName() << std::endl;
     }
     // output sigmoid parameter
-  output_file << "sigmoid=" << sigmoid_ << std::endl;
+    ss << "sigmoid=" << sigmoid_ << std::endl;
 
-  output_file << "feature_names=" << Common::Join(feature_names_, " ") << std::endl;
+    ss << "feature_names=" << Common::Join(feature_names_, " ") << std::endl;
 
-  output_file << std::endl;
+    ss << std::endl;
     int num_used_model = static_cast<int>(models_.size());
-  if (num_iteration > 0) {
-    num_used_model = std::min(num_iteration * num_class_, num_used_model);
+    if (num_iterations > 0) {
+      num_used_model = std::min(num_iterations * num_class_, num_used_model);
     }
     // output tree models
     for (int i = 0; i < num_used_model; ++i) {
-    output_file << "Tree=" << i << std::endl;
-    output_file << models_[i]->ToString() << std::endl;
+      ss << "Tree=" << i << std::endl;
+      ss << models_[i]->ToString() << std::endl;
     }
 
     std::vector<std::pair<size_t, std::string>> pairs = FeatureImportance();
-  output_file << std::endl << "feature importances:" << std::endl;
+    ss << std::endl << "feature importances:" << std::endl;
     for (size_t i = 0; i < pairs.size(); ++i) {
-    output_file << pairs[i].second << "=" << std::to_string(pairs[i].first) << std::endl;
+      ss << pairs[i].second << "=" << std::to_string(pairs[i].first) << std::endl;
     }
 
-  output_file << std::endl << "feature information:" << std::endl;
+    ss << std::endl << "feature information:" << std::endl;
     for (size_t i = 0; i < max_feature_idx_ + 1; ++i) {
-    output_file << feature_names_[i] << "=" << feature_infos_[i] << std::endl;
+      ss << feature_names_[i] << "=" << feature_infos_[i] << std::endl;
     }
 
+    return ss.str();
+}
+
+bool GBDT::SaveModelToFile(int num_iteration, const char* filename) const {
+  /*! \brief File to write models */
+  std::ofstream output_file;
+  output_file.open(filename);
+
+  output_file << SaveModelToString(num_iteration);
+
   output_file.close();
 
   return (bool)output_file;

src/boosting/gbdt.h

@@ -158,6 +158,13 @@ public:
   */
   virtual bool SaveModelToFile(int num_iterations, const char* filename) const override ;
 
+  /*!
+  * \brief Save model to string
+  * \param num_used_model Number of model that want to save, -1 means save all
+  * \return Non-empty string if succeeded
+  */
+  virtual std::string SaveModelToString(int num_iterations) const override ;
+
   /*!
   * \brief Restore from a serialized string
   */