# Format Correctness

The correctness of formats cannot be evaluated at compile-time. In fact, no format can be checked completely at compile-time because the final appearance on paper or on the screen must be checked by a human in each case.

It is possible to check the correctness of formats at run-time thanks to preconditions:

1. about the syntactical correctness of the format string.
2. about the relation between the format string and the other parameters.

Therefore, the approach is not completely unsafe. Part of the class declaration is a set of routines that check the format string and parameters.