Question

Well, i’ve read some months ago another “well know” C book(in my language), and i never learn’t nothing about this. The way that K&R writes 3 chapters in 20 pages it’s simply amazing, and of course that i can’t expect huge explanations, but that also rises questions.

I have a question about this point 1.5.1
The book says(pag 16):

main(){
  int c;// <-- Here is the question
  c=getchar();
  while (c != EOF){
    putchar(c);
    c = getchar();
  }
}

[…] The type char is specifically meant for storing such character
data, but any integer type can be used. We used int for a subtle but
important reason.
The problem is distinguishing the end of input from
valid data. The solution is that getchar returns a distinctive value
when there is no more input, a value that cannot be cinfused with any
real character. This value is called EOF, for “end of file”. We must
declare c to be a type big enought to hold any value that getchar
returns. We can’t use char since c must be big enough to hold EOF in
addition to any possible char. Therefore we use int.[…]

After searching google for another explanation:

EOF is a special macro representing End Of File (Linux: use CTRL+d on
the keyboard to create this, Windows command: use CTRL+z (may have to
be at beginning of new line, followed by RETURN)): Often EOF = -1, but
implementation dependent. Must be a value that is not a valid value
for any possible character. For this reason, c is of type int (not
char as one may have expected).

So i modified source from int to char to see what is the problem, about taking EOF values… but there is no problem. Works the same way.

I also didn’t undestrood how does getchar takes every character i write, and prints everything. Int type is 4bytes long, so it can take 4 characters inside a variable.
But i can put any number of characters, it will read and write everything the same way.
And with char, happens the same…
What does really happens? Where are the values stored when there are more than 1-4 characters?

Answer 1

So i modified source from int to char to see what is the problem,
about taking EOF values… but there is no problem. Works the same way

I happens to work the same way. It all depends on the real type of char, i.e. if it’s signed or unsigned. There’s also a C FAQ about this very subject. You’re more likely to see the bug if your chars are unsigned.

The bug can go undetected for a long time, however, if chars are
signed and if the input is all 7-bit characters.

EDIT

The last question is: char type is one byte long, and int is 4bytes
long. So, char will only take one ascii character. But if i type
“stack overflow is over 1byte long”, the output will be “stack
overflow is over 1byte long”. Where is “tack overflow is over 1byte
long” stored, and how does putchar, puts an entire string

Each character will be stored by c in turn. So the first time, getchar() will return s, and putchar will send it on its way. Then t will come along and so on. At no point will c store more than one character. So although you feed it a large string, it deals with it by eating one character at a time.