* enh via tz:
> does anyone implement the ungetc() part or am i misunderstanding what
> that's trying to say?
>
> #include <stdio.h>
> int main() {
> FILE* fp = fopen("/tmp/x.c", "r");
> ungetc('x', fp);
> printf("%c\n", fgetc(fp));
> fclose(fp);
>
> fp = fopen("/tmp/x.c", "r");
> ungetc('x', fp);
> fflush(fp);
> printf("%c\n", fgetc(fp));
> fclose(fp);
>
> return 0;
> }
>
> where this file is /tmp/x.c gives me x and # whether or not the flush
> is there, for both glibc and macOS.
Not sure if this is what you mean. We changed glibc fairly recently:
commit 377e9733b50ce41e496c467ddcc112f73c88f3bd
Author: Joseph Myers <[email protected]>
Date: Tue Jan 28 19:38:27 2025 +0000
Fix fflush after ungetc on input file (bug 5994)
As discussed in bug 5994 (plus duplicates), POSIX requires fflush
after ungetc to discard pushed-back characters but preserve the file
position indicator. For this purpose, each ungetc decrements the file
position indicator by 1; it is unspecified after ungetc at the start
of the file, and after ungetwc, so no special handling is needed for
either of those cases.
This is fixed with appropriate logic in _IO_new_file_sync. I haven't
made any attempt to test or change things in this area for the "old"
functions; the case of files using mmap is addressed in a subsequent
patch (and there seem to be no problems in this area with files opened
with fmemopen).
Tested for x86_64.
Thanks,
Florian
