assigned to @mclow

This is odd.

<__locale> includes (line 20), which includes <ctype.h> (line 39)

So you should be getting the definition of isascii.

Can you run the compile line again, removing the -c and using '-E' instead?
That should give some preprocessed output, and we can see the exact sequence of includes.

-E output part1

-E part2

newlib's ctype.h
After examining the -E output, I see that newlib's ctype.h is picked up. The isascii declarations are guarded, though:

#if (__MISC_VISIBLE || __XSI_VISIBLE) && !defined _AEABI_PORTABLE
int _EXFUN(isascii, (int __c));
int _EXFUN(toascii, (int __c));
#define _tolower(__c) ((unsigned char)(__c) - 'A' + 'a')
#define _toupper(__c) ((unsigned char)(__c) - 'a' + 'A')
#endif

I don't know whether libcxx's use of isascii ought to be changed or if my defines wrt to newlib are incorrect. Do you know?

Thanks,
Catherine

I don't know whether libcxx's use of isascii ought to be changed or if my
defines wrt to newlib are incorrect. Do you know?

No; I don't know. I suspect that you should define __MISC_VISIBLE to 1.
But I'm not a Newlib expert, so that's just a guess.

Do you have an update on this?
Is this a newlib problem? (because I can't see anything that libc++ is doing wrong here)

No, I don't have an update and I'm not currently tracking this problem. I will close it out and resubmit if we encounter in the future.

Thanks,
Catherine