-XBT_PRIVATE FILE* surf_fopen(std::string name, const char* mode);
-XBT_PRIVATE std::ifstream* surf_ifsopen(std::string name);
+XBT_PRIVATE FILE* surf_fopen(const std::string& name, const char* mode);
+XBT_PRIVATE std::ifstream* surf_ifsopen(const std::string& name);