How to properly using EOF?

I have question about EOF.

First of all, I am coding a simple program that is coping/printing the user's input.

However, the program copies the EOF also in the output.

For an example, my O.S is Window and my EOF works when I type (Enter -> cntrl + z -> Enter) in order. If I input "Hello" + Enter + EOF key combination, the output prints the weird letter('?') at the end of the copied user input.

How can I get rid of the '?' at the end of the output, and why is it happening?

#include <stdio.h>

void copy(char to, char from);

main()
{
int i;
int c;

char origin[10];
char copied[10];

for(i = 0; (c = getchar()) != EOF; ++i)
{
origin[i] = c;
}

copy(copied, origin);


for(i = 0; i < 10; i++)
putchar(copied[i]);



}

void copy(char to, char from)
{
int i;

i = 0;
while((to[i] = from[i]) != '')
i++;
}


int main(void)

main()

EOF

char

char

unsigned

EOF

EOF

4 Answers
4

The problem is not related to EOF at all, there are multiple issues in your code leading to potential undefined behavior and unwanted side-effects:

EOF

origin

origin

stdin

copy

stdin

while((to[i] = from[i]) != '')

origin

copied

copied

origin

copy

stdout

copied

main

int main(void)

Here is a corrected version:

#include <stdio.h>

void copy(char to, char from);

int main(void) {
int i;
int c;
char origin[10];
char copied[10];

for (i = 0; i < 10 - 1 && (c = getchar()) != EOF; i++) {
origin[i] = c;
}
origin[i] = '';

copy(copied, origin);

for (i = 0; copied[i] != ''; i++) {
putchar(copied[i]);
}

return 0;
}

void copy(char to, char from) {
int i;

i = 0;
while ((to[i] = from[i]) != '')
i++;
}


You forgot to NUL-terminate origin. So you invoke Undefined Behavior during copying. Use the following code to get input instead:

origin

for(i = 0; i < 9 && (c = getchar()) != EOF; ++i) /* `i < 9` to prevent array overruns */
{
origin[i] = c;
}
origin[i] = ''; /* NUL-terminate your string */


Also change the printing code to:

for(i = 0; copied[i] != ''; i++) /* Print until a NUL-terminator */
putchar(copied[i]);


origin[i] = '';

origin

You are unconditionally outputting all 10 members of your array.
You could fix by appending the often used '' at the end of the letters to output.
With a

''

origin[i] = '';


after reading in.

And finally outputting until that marker, instead of everything

for(i = 0; copied[i]!=''; i++)


This keeps your assumption that the arrays are large enough to keep the input (including the added ''). You should however protect against that, e.g by using a dual condition for any loop, checking against accessing beyound the highest allowed array index.

''

for(i = 0; (c = getchar()) != EOF; ++i)

"Hello Newb<nasty shellcode>"

You are using an IDE (probably CodeBlocks) which is using page buffer between subsequent IO operation and that's why you actually get the output.

Next, you are forcing to print all ten elements of the array in the output for loop which is bad coding practice.

This simple snippet could help you

scanf("%10[^n]s",input);


Use it to read input from file ./youpro < file_name_where_to_fetch_input

Thanks to David C. Rankin in the comment to mention the error.

EOF

Ctrl+d

EOF

Ctrl+z

s

scanf("%9[^n]", origin);

scanf()

scanf()

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