One additional note, I could not find the source for Catalina. But in precedent versions of macOS, the code of ungetc is different depending on the fact that we push back the same character or not.

https://opensource.apple.com/source/Libc/Libc-1272.250.1/stdio/FreeBSD/ungetc.c.auto.html

In the first case, it's a simple rewind of the file pointer. In the second case, a buffer is used. That could explain why I see different behaviors depending on the fact that we push back the same character that was read and why it can interfere with ftell.

[espeak-ng:master] New Comment on Issue #674 Build fails on MacOS Catalina
By BenTalagan:

One additional note, I could not find the source for Catalina. But in precedent versions of macOS, the code of ungetc is different depending on the fact that we push back the same character or not.

ungetc.c

In the first case, it's a simple rewind of the file pointer. In the second case, a buffer is used. That could explain why I see different behaviors depending on the fact that we push back the same character that was read and why it can interfere with ftell.

[espeak-ng:master] New Comment on Issue #674 Build fails on MacOS Catalina
By rhdunn:

Interesting. Thanks.

I wonder what is causing espeak to unget a character different to the previously read character. Maybe addressing that will fix the issue you are seeing on the Mac (and possibly on other BSD-based platforms).