Are you familiar with preprocessor directives?
They have been integral part of C since its conception.
If you are not (familiar with preprocessor ) , how posting the entire several hundreds lines of text will help (you) to understand the issue ?

yes i am familiar with this concept, thank you,
Nevertheless everything inside conditional preprocessor directives must be valid C++, which arbitrary text is not.

I asked for a bigger snippet to get an idea where and how your noted text is used exactly.

Are you familiar with preprocessor directives?

I suspect @raven-worx is perfectly familiar with C, C++, preprocessors and other such :)

that should include " ' "

No. C++ preprocessor tokenizes input. This is different from the old C preprocessor behaviour. You can't assume everything is identical. It looks for " (double-quote) as potential strings but also ' (single-quote) as potential literal character sequences. These could be unterminated.

You could read:
https://gcc.gnu.org/onlinedocs/cpp/Tokenization.html#Tokenization
https://gcc.gnu.org/onlinedocs/cpp/Traditional-lexical-analysis.html#Traditional-lexical-analysis

You seem to have a single single-quote on a line. You are likely to have that reported as "an unterminated character". It is perhaps a warning rather than error. Behaviour varies by compiler.

Needless to say, this is from whatever C++ compiler you are using. Nothing to do with Qt or Creator. I don't know who you have in mind for reporting a bug to.

One online compiler (gcc):

// Example program
int main()
{
#ifdef UNUSED
Ignore this
but can't have this single quote
#endif
}

generates compiler warning:
6:8: warning: missing terminating ' character

You can look at it via https://godbolt.org/z/Px9WanYWW

Commenting your "free text" lines by // ... would avoid the problem.

@AnneRanch
but the line containing the error is not C++, thus an error is expected.

It does NOT ignore " ' " . Why?

why do you expect it to be ignored?
show the whole snippet of code please.

Are you familiar with preprocessor directives?
They have been integral part of C since its conception.
If you are not (familiar with preprocessor ) , how posting the entire several hundreds lines of text will help (you) to understand the issue ?

#ifdef BYPASS

do not process what is inside here
unless BYPASS is define(d)
that should include " ' "

#endif

It does NOT ignore " ' " . Why?

why do you expect it to be ignored?
show the whole snippet of code please.

@AnneRanch
sure, this isnt C++

To whom ( the bell tools ) ?
preprocessor r forum ?