EOF in C, what is EOF?

Question

I have some questions about EOF in C.

1. What is actually EOF? I have read that it is a macro that "expands" to -1. What does this mean? Specifcally what does "expand" mean in this case?

I have this code:

#include <stdio.h>

int main()
{
    int c;
    scanf("%d", &c);
    if (c==EOF){printf("c is EOF");}
    else {printf("C is not EOF");}
}

Output:

1
C is not EOF
    
-1
c is EOF
    
^Z

2. In the code, if I write -1, I get that this is EOF. But from what I have read, EOF is not really -1, because we can write -1 at the end of a file?

3. I have read that on windows to get EOF you need to type CTRL+Z. But when I try to type this and press enter in the terminal, nothing happens, as I demonstrate in the last example in the code. What am I doing wrong?

Answer 1

What is actually EOF? I have read that it is a macro that "expands" to -1. What does this mean? Specifically what does "expand" mean in this case?

It means that it is defined as C macro for example:

#define EOF -1

What is EOF?

EOF indicates that the last operation on the file or stream has reached its end.

The C preprocessor textually replaces occurrences of the EOF in your source code with -1

Your code is wrong. scanf returns EOF not scans it. It should be:

int main()
{
    int c, val;
    c = scanf("%d", &val);
    if (c==EOF){printf("c is EOF");}
    else {printf("C is not EOF");}
}

But scanf will almost never return EOF unless you provide a special key combination to force it.