fix data_filename_ bug with c_api

include/LightGBM/dataset.h

@@ -219,7 +219,7 @@ private:
   /*! \brief Load query wights */
   void LoadQueryWeights();
   /*! \brief Filename of current data */
-  const char* data_filename_;
+  std::string data_filename_;
   /*! \brief Number of data */
   data_size_t num_data_;
   /*! \brief Number of weights, used to check correct weight file */
@@ -546,7 +546,7 @@ public:
   Dataset(const Dataset&) = delete;
 
 private:
-  const char* data_filename_;
+  std::string data_filename_;
   /*! \brief Store used features */
   std::vector<std::unique_ptr<FeatureGroup>> feature_groups_;
   /*! \brief Mapper from real feature index to used index*/

src/io/dataset.cpp

@@ -511,7 +511,7 @@ bool Dataset::GetIntField(const char* field_name, data_size_t* out_len, const in
 
 void Dataset::SaveBinaryFile(const char* bin_filename) {
   if (bin_filename != nullptr
-      && std::string(bin_filename) == std::string(data_filename_)) {
+      && std::string(bin_filename) == data_filename_) {
     Log::Warning("Bianry file %s already existed", bin_filename);
     return;
   }

src/io/dataset_loader.cpp

@@ -608,10 +608,10 @@ Dataset* DatasetLoader::CostructFromSampleData(double** sample_values,
 
 void DatasetLoader::CheckDataset(const Dataset* dataset) {
   if (dataset->num_data_ <= 0) {
-    Log::Fatal("Data file %s is empty", dataset->data_filename_);
+    Log::Fatal("Data file %s is empty", dataset->data_filename_.c_str());
   }
   if (dataset->feature_groups_.empty()) {
-    Log::Fatal("No usable features in data file %s", dataset->data_filename_);
+    Log::Fatal("No usable features in data file %s", dataset->data_filename_.c_str());
   }
   if (dataset->feature_names_.size() != static_cast<size_t>(dataset->num_total_features_)) {
     Log::Fatal("Size of feature name error, should be %d, got %d", dataset->num_total_features_,