The C17 (N2176) standard states, "The fputc function returns the character written" (7.21.7.3) if there is no write error.

But in the context of

int c ;
// ... later, c is assigned an "interesting" value ...
int k = fputc ( c , stdout ) ;

is

k == c || k == EOF

always true? I.e., provided that fputc does not return EOF, is it guaranteed to return c? Put a third way, can fputc write a character other than one equal to its first argument?

For example If I request output of the dollar sign (not guaranteed to be in the source or execution character sets, AFAICT), could '\u0024' != fputc('\u0024', stdout). Maybe the program will output a local currency symbol, instead.

CodePudding user response：

is k == c || k == EOF always true?

Usualy yes, but no.

With fputc ( c , stdout ), c is converted to an unsigned char and that is written. It is that value, or EOF that is returned.

Instead, expect k == (unsigned char) c || k == EOF.

CodePudding user response：

Yes, fputc always returns either EOF or the written character.

Per cppreference.com's page on fputc:

Return value
On success, returns the written character.
On failure, returns EOF and sets the error indicator (see ferror()) on stream.

And from the C17 standard (7.21.7.3/3 "The fputc function", N2310):

Returns
The fputc function returns the character written. If a write error occurs, the error indicator for the stream is set and fputc returns EOF.