I don't see where the standard requires that EOF has to be different
from any possible char value.
EOF must have type int and be negative. On those systems where char
is unsigned, it obviously cannot be a char value.
It could be a valid char on a system where char is signed. But, as
explained below, none of the normal character I/O functions can return
any negative value other than for end of file or I/O error
If EOF is a valid char value, you could just check the feof()
function. For example, the following program should copy stdin to
stdout on such an implementation:
#include <stdio.h>
int main(void)
{
int c;
while (c = getchar(), c != EOF && !feof(stdin) && !ferror(stdin)) {
Coding problem here:
If c == EOF, then the remaining to expressions following the
first && will never be evaluated due to && short circuit. The while
will evaluate to false and the loop terminated immediately, regardless
of the status of feof and ferror. Consequently, you don't know if you
have hit the real EOF or the merely a character that looks like it.
If c != EOF, you are pretty much guaranteed that !feof() and
!ferror will both be true also.
Therefore, the expression c != EOF defeats the purpose of what
you want the expression after the comma to do.
Logic problem also:
getchar "returns the next character of [stdin] as an unsigned
char (converted to an int), or an EOF if end of file or error occurs"
(from K&R2, B1.4). Since an unsigned int cannot be negative and EOF
has to be, getchar cannot return EOF for a normal character.
putchar(c);
}
return 0;
}
The comparison to EOF could be omitted, but it might save the overhead
of some function calls.
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