Is casting of infinity to integer undefined?

Question

Is the casting of infinity (represented by float) to an integer an undefined behavior?

The standard says:

4.10 Floating-integral conversions<

Answer 1

You said

I can't tell whether "truncated value cannot be represented" covers infinity

but it all boils down to

What is the result of truncating infinity.

The C standard (incorporated into C++ via 26.9) answers that quite plainly:

Since truncation of infinity is still infinity, and infinity cannot be represented in int (I hope there's no question about this part), the behavior is undefined.