Add a function to free the memory allocated when calling GetStringFlag

PiperOrigin-RevId: 731778685

connections/c/nc.cc

@@ -103,7 +103,9 @@ class FlagReaderWrapper : public nearby::flags::FlagReader {
     };
     NC_DATA flag_value = phenotype_flag_reader_.get_string_flag_value(
         context_, &flag_name, &default_value);
-    return std::string(flag_value.data, flag_value.size);
+    std::string ret = std::string(flag_value.data, flag_value.size);
+    phenotype_flag_reader_.free_string_value(&flag_value);
+    return ret;
   }
 
  private:

connections/c/nc_types.h

@@ -337,6 +337,8 @@ typedef struct NC_PHENOTYPE_FLAG_READER {
   const NC_DATA (*get_string_flag_value)(READER_CONTEXT context,
                                          const NC_DATA* flag_name,
                                          const NC_DATA* default_value);
+  // Frees a string allocated when calling get_string_flag_value.
+  const void (*free_string_value)(const NC_DATA* value);
 } NC_PHENOTYPE_FLAG_READER;
 
 #ifdef __cplusplus