Thread: putchar vs. printf. why difference in output?

Hi everyone,

This is my first post on this forum & I hope to hang around for a long time. I have started learning C as hobbyist. CPL by Kernighan & Ritchie is my main book and Google a sidekick .

In one of the exercise in the book the value of EOF is asked to be printed. I used two methods:

#include <stdio.h>

main()
{
printf("The value of EOF is %d\n\n", EOF);


}

and

#include <stdio.h>

main()
{
putchar (EOF);

}

The output I get are different in both the cases. Why is that so?

putchar() writes the character c, cast to an unsigned char, to stream.
EOF is usually -1. printf %d just print argument as int. Thus -1 printed.

putchar actually puts the integer c to the stream: it just uses the first byte. I think the issue here is that whatever EOF is, it's non-printable as a character, so that is your difference in output. printf displays EOF's value, which is not the same obviously.

Code:

#include <assert.h>
#include <ctype.h>
#include <stdio.h>
int main(void)
{
        assert(isprint(EOF));
        return 0;
}

Assertion fails every time.

Thanks indeed for help guys! That cleared my confusion.