(C/C++) EOF in windows7

Question

#include <cstdio>

void fcopy(FILE* from, FILE* to);

int main()
{
    fcopy(stdin, stdout);
    return 0;
}

void fcopy(FILE* from, FILE* to)
{
    int c;
    while ((c = getc(from)) != EOF) {
        putc(c, to);
    }
}

When I run this program, some unexpected behaviour happens with ^Z (Ctrl+z), which I would use to indicate EOF.

My input of "hello\\n" executes the while loop in 'fcopy' to print the same.

"^Z\\n" ends the program.

But if I input "blahblah^Zasdfasdf\\n", while I expected the program to print "blahblah" and terminate, it prints "blahblah→" with a little arrow and waits for my input. Whatever I write down here will be copied down exactly the same; it seems to re-execute the loop while cutting away anything written after '^Z'.

in: hello
out: hello

in: hello^Z
out/in: hello→?? // "??" is my input
out: ??

in: ^Z
termination

Could anyone please clarify why the program works that way? Thanks for any help, in advance.

Answer 1

This is because the Windows terminal program, which is what is reading your keyboard input and passing it on to your program, is handling Ctrl+Z like that. It only means "signal end of input" when pressed at the start of a line.

Note that EOF in C does not represent an actual ("physical") character, it's out-of-band signalling to indicate that "there was no character to be read, since the file has ended".

Answer 2

In general I would expect you that you should wait for ^Z and not EOF. ^Z is 0x1A ASCII character ( http://en.wikipedia.org/wiki/Substitute_character ). Also, you should definitely also check for EOF since file can end without ^Z

It seems that for some reason, console applications interpret ^Z as EOF when line is empty (I'm not sure why though - This could be legitimate behavior or simply a bug as suggested in https://connect.microsoft.com/VisualStudio/feedback/details/798951/c-getc-breaks-when-encountering-character-26-or-1a-hex-ascii-sub )

But the following code fixes it:

#include <cstdio>

#define CTRL_Z_SUB 0x1A // CTRL_Z substitue ASCII key

void fcopy(FILE* from, FILE* to);

int main()
{
    fcopy(stdin, stdout);
    return 0;
}

void fcopy(FILE* from, FILE* to)
{
    int c = getc(from);

    while (c != EOF && c != CTRL_Z_SUB) {
        putc(c, to);
        c = getc(from);
    }
}