C++03 Standard defines well-formed program (1.3.14 [defns.well.formed]) as
a C++ program constructed according to the syntax rules, diagnosable semantic rules, and the One Definition Rule (3.2)
It further defines an ill-formed program (1.3.4 [defns.ill.formed]) as
input to a C++ implementation that is not a well-formed program (1.3.14)
and the Standard is full of statements such as "if X then the program is ill-formed" for example (2.13.1/3):
A program is ill-formed if one of its translation units contains an integer literal that cannot be represented by any of the allowed types.
Yet I haven't found what the C++ implementation is required to do with ill-formed programs.
Suppose I have an ill-formed program. Now what?
Is the C++ implementation required to do something specific when it encounters an ill-formed program or is the C++ implementation behavior just undefined?