Why is char initialized to 0xFF ?

[Ola Fosheim Grøstad]

On Sunday, 9 June 2019 at 08:36:30 UTC, Patrick Schluter wrote:
> No, by putting NaN in d you hav e a deterministic error. In C 
> and C++ you will have undefined behaviour that will vary with 
> compiler, version, options, OS version, architecture, position 
> of the moon, etc. and sometimes undetectable bugs.

I don't think it is undefined though… If something has an 
arbitrary value, you could still compute with it, if the 
algorithm takes that into account. Assuming that all bit-patterns 
provides a defined value (which is the case for IEEE floating 
point bit-patterns).

Anyway, the obvious advantage with having structs default 
initialized to all-bits-zero is that you can have an allocator 
that clears bits in the background (bypassing caches so they are 
not polluted).

Then you have no penalty when allocating an array of one million 
struct values. Which is very useful. Just allocate memory-chunks 
that are already set to zero-bits.

You usually want an array of floating point values to be 
pre-initialized to zeros. You almost never want an array of 
floating point values being initialized to NaN.