a question about POSIX fgetc

[Pietro Monteiro]

On Thu, Jul 2, 2026, at 10:29 PM, chris hermansen wrote:
> Good evening all;
>
> At https://gcc.gnu.org/onlinedocs/ga68/POSIX-string-transput.html I see 
> fgetc defined as:
>
> Procedure: *fgetc* `= (*int* fd) *int*` 
> <https://gcc.gnu.org/onlinedocs/ga68/POSIX-string-transput.html#index-fgetc>
> Read a character from the file with descriptor `fd`. This procedure 
> yields the read character in case a valid Unicode character got 
> successfully read. If an unrecognizable or unknown character is found 
> then this procedure yields `replacement char`. In case of end of file 
> this procedure yields `eof char`. 
>
> However when I look in libga68/posix.a68 I see:
>
> pub proc(int)char        fgetc = nest C "_libga68_posixfgetc";
>
> Digging further into libga68/ga68-posix.c I see that 
> _libga68_posixfgetc returns uint32_t and the values can be 
> EOF_PSEUDO_CHARACTER (== -1), REPLACEMENT_CHARACTER (0xFFFD) or the 
> successfully decoded uint32_t "res".
>
> My C ignorance is showing here but I'm having difficulty understanding 
> what -1 or 0xFFFD look like when returned as unit32_t and what those 
> values end up looking like in GNU Algol 68.

We use UTF-32 for chars, so the C unit32_t will be a regular char on the A68 side.
0xFFFD is the “question mark in a box” (�).
-1 will become 0xFFFFFF, since we use an unsigned type.

> Should I be doing something like
>
> int ic = REPR fgetc(fd) so that I can check to see if I've hit end of 
> file or a replacement character?

You can use the “string break” notation "'(uhhhh)" or "'(Uhhhhhhhh)”\

https://gcc.gnu.org/onlinedocs/gcc-16.1.0/ga68/String-breaks.html

> Please advise!

Hope that helps.

pietro

> -- 
> Chris Hermansen · clhermansen "at" gmail "dot" com
>
> C'est ma façon de parler.