George:

I meant:

For unsigned int, %d will only work if the value is not bigger than the
largest allowed value of int. Otherwise, a negative value will be
displayed. %u should be used with unsigned int.

%d is intended for use with int, and either positive or negative values
may be displayed.

Although not so well suited to localization, C++ streams handle this
issue much better, because they are overloaded for different types.