C、为什么printf要在一位数长后加一个“D”？

Question

I'm working through the K&R C book and one of the example programs is this:

#include <stdio.h>

int main() {
    long nc;

    nc = 0;
    while (getchar() != EOF) {
        ++nc;
    }
    printf("%ld", nc);

    return 0;
}

When I run this program, it mostly behaves as I expect. So for an input like This is a sentence , it prints 19 .

However, if I input anything under 10 characters (including EOF), there is a capital D appended to the output number.

Eg for input hello , the output is 6D .

Why is there a D appended to an integer value and what does it mean?

Note: This occurs with cc , gcc and clang .

Answer 1

It turns out that D is part of the ^D that gets printed to the console when I input an EOF ( control + D on Unix). Because there is no \\n at the start of the printf statement, a single-digit number will overwrite the ^ , while a double-digit number will overwrite the entire ^D , which is what gave the impression of some weird behaviour.

Answer 2

What version of gcc are you using? I ran the exact same code using gcc and it runs fine. Maybe it's an artifact left over by your terminal where it's trying to print the Ctrl-D for end of file