Thread: getchar()

Code:

#include<stdio.h>

int main ()
{
	int c;

   while((c=getchar()) !=EOF)
   	putchar(c);
}

getchar takes one character from the stadin and putchar should
print that character before any more input.

then
why the output is

hello
hello

instead of hheelllloo

Because it's buffered. Flush your output stream each time through the loop.

Quzah.

No, this is good code appearing in K&R

That means jack and squat to me. There are plenty of examples of bad code that is published.

An integer is used because EOF is -1 on some systems.

Just because it works on some systems is no reason to say its correct.

By defination getchar will only return EOF when "on end of file or error." Now lets see are we reading from a file? Nope. The chance of an error occuring? Slim to none.

Edit: No overflow problems with 1420 characters buffered.

That means jack and squat to me. There are plenty of examples of bad code that is

Perhaps. The author of c doesn't make too many blatant errors though. The reason why this code does not use a user interface that you are used to is that in unix(and in dos) you can let stdin be a file by doing something like ./prog < file.txt EOF can be returned upon user input but this depends on what OS. C-d for unix and C-z for windows

Correctness is a difficult property to define. It's entirely what the author of the code wants.

I believe that the stdout buffers might be flushed when stdin is accessed. This is the way with C++, I think. Try this program

Code:

#include <stdio.h>

int main(void) { printf("hello"); }

On my system there is no output.

Originally posted by Thantos
1) Don't use EOF. Test it against '\n'

Why not? EOF is a valid test.

Originally posted by Thantos
2) The process won't even go into the loop until the Enter key is pressed. Once it the enter key is pressed then the loops starts and getchar() gets the letters from the buffer for the input stream.

In the provided (first post) example, yes. But not if you add a fflush call to the loop like I suggested.

Originally posted by Thantos
3) You are saying c is an integer but you are assigning it a character. See the problem here?

No. There is no problem. In fact, this is exactly how you want to test characters, as integers, not as char.

You cannot test EOF with a char data type. For that matter, take a look at some standard library functions for use with characters:

int getc(FILE *stream);
int getchar(void);
int isalnum (int c);
int isalpha (int c);
int iscntrl (int c);
int isdigit (int c);
int isgraph (int c);
int islower (int c);
int isprint (int c);
int ispunct (int c);
int isspace (int c);
int isupper (int c);
int isxdigit (int c);

Now this may not mean "jack and squat" to you, but it does mean something to the ANSI standard committee. So perhaps you should take it up with them?

Quzah.

Originally posted by Thantos
But it doesn't work for what they are trying to do. If they were trying to read from a file its all good. However from the output they gave its pretty obvious they are not. So using input from stdin there is no way to end the program normally. How did I come to this conculsion, by running the dang program.

I'll admit I was wrong on the int part. But I will not conced the EOF part due to what the orginal poster gave as their output.

Well you're wrong again. Depending on your OS you can send EOF from the console by using CTRL+Z or CTRL+D usually.

Quzah.

>What about the OS's that can't?
This is a stretch. Name an operating system that is unable to signal EOF and supports interactive input.

>And I try to avoid having to use escape characters to terminate a program.
Why? If you're reading characters and every character is valid input, how do you terminate the program without placing extra restrictions on valid input or using an interactive option mechanism that would be awkward (at best).