C++ Strip non-ASCII Characters from string

Question

Before you get started; yes I know this is a duplicate question and yes I have looked at the posted solutions. My problem is I could not get them to work.

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Answer 1

At least one problem is in your invalidChar function. It should be:

return !isprint( static_cast( c ) );

Casting a char to an unsigned is likely to give some very, very big values if the char is negative (UNIT_MAX+1 + c). Passing such a value toisprint` is undefined behavior.