Re: C90 fpeek

On Fri, 24 Jan 2025 09:24:35 -0500
James Kuyper <jameskuyper@alumni.caltech.edu> wrote:

On 1/24/25 00:13, Keith Thompson wrote:

"Paul Edwards" <mutazilah@gmail.com> writes:
[...] 

With the benefit of hindsight, is there any reason why fpeek
couldn't have been added to C90, with implementations
being allowed with just a macro that returns some sort of
"unsupported"?
>
If fpeek (or similar) makes sense, can someone suggest an
appropriate interface? 

[...]
 
It would help to know what "fpeek" is supposed to do.  There no such
function in any edition of the C standard or in any implementation
that I'm aware of. 

 
A google search uncovered a stackoverflow question for which the
answer was:
 
int fpeek(FILE *stream)
{
    int c;
 
    c = fgetc(stream);
    ungetc(c, stream);
 
    return c;
}
 
I don't see any reason why such a function is needed in the standard
library. However, if it were added, since fgetc() and ungetc() are
mandatory for hosted implementations, I also see no reason to allow
for it to be unsupported.

It can be supported, but not useful for OP's purouses without ability
to set file to O_NONBLOCK. Which, I would think, is outside of C
standard.