Question about EOF (C)

xailer · 12-06-2003, 12:14 PM

hi
I'm learning C using red hat 9

EOF marks the end of file.But what value does EOF represent?First I thought it was either 1 or 0,but none of them works.So I tried this

main()
{
#define EOF 3

int a;

a=getchar();
while(a!=EOF)
{
putchar(a);
getchar(c),
}
}

But loop just didn't want to end,no matter what I pressed.

So what value does EOF hold and why it didn't work even with #define
statement?

thank you

ter_roshak · 12-06-2003, 12:21 PM

I believe the value returned is -1, and I just tested it with the following code:

void main()
{
printf("%i\n", EOF) ;
}

...and I received a -1 response.

Josh

xailer · 12-06-2003, 12:35 PM

I get -1 also,but why is -1 ignored in while loop?

bye

teval · 12-06-2003, 12:46 PM

EOF is generated with ^D (ctrl + D)

I can tell you why it didn't work too

Your program is definitely not doing what you want it to do.

Code:

int main()
	{
//		#define EOF 3
// Redefining things like EOF is bad, don't do it.
// Some libs may use EOF and if you redefine it, it might break a lot of things

	int a;

	a = getchar(); //Note how it's in [ code] and [/ code] tags, it's indented and spaced out
	// It not only looks better, but it's simpler to read

	while( a != EOF ) // You had = instead of ==, what that would do is assing a the value of EOF
        // != is more logical than a! == EOF
        // You are not flipping the value of a and then comparing, you are comparing and seeing if they are differnet
	// That assignment should always return true, because unless you've used all your computer's memory it won't fail
	{
		putchar(a);
		getchar(a); //Note the fact that it's a all the time, you had c, but I think that was a typo.
	}

	retrun 0; //It's nice when main returns a value, since when you string programs togeather with && it'll cause the entire chain to fail if it's non 0
	//Also a nice way of testing of programs failed or worked
}

I suggest scrapping the code, and doing something else like..
making it stop at a newline (\n)

xailer · 12-06-2003, 01:11 PM

hi
Yes,c was a typo.
I copyed this exaple from book.

Quote:

Originally posted by teval

while( a != EOF )
// != is more logical than a! == EOF
// You are not flipping the value of a and then comparing, you are comparing and seeing if they are differnet
// That assignment should always return true, because unless you've used all your computer's memory it won't fail

Are you reffering to what would happened if I had
while (a! == EOF) ;

statement?

Is -1 not recognised as EOF because the value that I type in is essentially
a char,and EOF is integer?

thank you for helping

teval · 12-06-2003, 08:13 PM

I'm saying, EOF is not the same as -1. EOF is ^D
Comes up as -1 because of the fact ^D doesn't map as a visible character

xailer · 12-07-2003, 11:15 AM

thanx for your help