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Full Discussion: Text stream K&R exercises
Operating Systems OS X (Apple) Text stream K&R exercises Post 302387199 by Jammer Six on Thursday 14th of January 2010 11:43:45 PM
Old 01-15-2010
Okay, I'm back. Smilie

I've been examining if.

For 1-6, I wrote this, thinking that perhaps I was just making it too complicated:

Code:
/*
 *  verify.c
 *  
 *	Exercise 1-6, Verify that the expression "getchar() != EOF is 0 or 1.
 */

#include <stdio.h>

main(){
	
	int v;
	
	while (v=(getchar() != EOF)) { // get another character, make the test
		
		printf("%d\n",v);	// prints as long as it isn't EOF
	}	// end of while
	
	printf("Reached EOF, program ends.\n\n");
	
}	// end of main

When I run it, I see a strange problem.

It produces a list of 1s, (because the statement is always true, if there's another character that isn't EOF) and then when you hit Control-D (Thank you, thank you!) it prints the end statement.

The problem is that it always prints one extra 1!

That is, if I type a string of five letters into the keyboard, it will print six ones.

I don't see where the extra one is coming from, the only way to reach the printf statement is for there to be a character in the character stream. I think. Maybe. Perhaps. Probably. In my fantasy world.

So where is the extra 1 coming from?

P.S. Now I'm off to nail 1-8, which looks easy.

---------- Post updated at 20:43 ---------- Previous update was at 20:32 ----------

Quote:
Originally Posted by gaurav1086
Which Operating System do you use?
Gaurav, thank you, I'm using Mac OX X, 10.6.2, called Snow Leopard, and Control-D does indeed work.

Thank you again. Smilie

Last edited by Jammer Six; 01-15-2010 at 12:39 AM.. Reason: P.S.
 

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GETS(3) 						     Linux Programmer's Manual							   GETS(3)

NAME
fgetc, fgets, getc, getchar, gets, ungetc - input of characters and strings SYNOPSIS
#include <stdio.h> int fgetc(FILE *stream); char *fgets(char *s, int size, FILE *stream); int getc(FILE *stream); int getchar(void); char *gets(char *s); int ungetc(int c, FILE *stream); DESCRIPTION
fgetc() reads the next character from stream and returns it as an unsigned char cast to an int, or EOF on end of file or error. getc() is equivalent to fgetc() except that it may be implemented as a macro which evaluates stream more than once. getchar() is equivalent to getc(stdin). gets() reads a line from stdin into the buffer pointed to by s until either a terminating newline or EOF, which it replaces with ''. No check for buffer overrun is performed (see BUGS below). fgets() reads in at most one less than size characters from stream and stores them into the buffer pointed to by s. Reading stops after an EOF or a newline. If a newline is read, it is stored into the buffer. A '' is stored after the last character in the buffer. ungetc() pushes c back to stream, cast to unsigned char, where it is available for subsequent read operations. Pushed - back characters will be returned in reverse order; only one pushback is guaranteed. Calls to the functions described here can be mixed with each other and with calls to other input functions from the stdio library for the same input stream. For non-locking counterparts, see unlocked_stdio(3). RETURN VALUE
fgetc(), getc() and getchar() return the character read as an unsigned char cast to an int or EOF on end of file or error. gets() and fgets() return s on success, and NULL on error or when end of file occurs while no characters have been read. ungetc() returns c on success, or EOF on error. CONFORMING TO
ANSI - C, POSIX.1 BUGS
Never use gets(). Because it is impossible to tell without knowing the data in advance how many characters gets() will read, and because gets() will continue to store characters past the end of the buffer, it is extremely dangerous to use. It has been used to break computer security. Use fgets() instead. It is not advisable to mix calls to input functions from the stdio library with low - level calls to read() for the file descriptor associ- ated with the input stream; the results will be undefined and very probably not what you want. SEE ALSO
read(2), write(2), ferror(3), fopen(3), fread(3), fseek(3), puts(3), scanf(3), unlocked_stdio(3) GNU
1993-04-04 GETS(3)
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