QDataStream with QFile don't work in classes

The attached file includes #define FAIL. When FAIL is uncommented, a QDataStream and QFile are created in a class. The for loop puts 1000 integers in fail.dmp but when the program finishes fail.dmp is empty. The issue is that the data in the QDataSream/QFile is not flushed because if the for loop iterates 5000 times some data does appear in the file. If the #define FAIL is commented out, the QDataStream and QFile are defined in main() and the program doesn't fail.