How to input eof(Ctrl+z) while letting the scanf have a space before the specifier to avoid getting previous \n error?

Asked Jan 05 '21 at 07:27

Active Jan 05 '21 at 07:31

Viewed 124 times

( I hit enter)

#include<stdio.h>
#include<stdlib.h>
int main(){
    int target,result;
    while(1){
        printf("Please input your target: ");
        scanf(" %d",&target);
        if(feof(stdin)){
            break;
        }
        printf("test\n");       
    }
}

if I chnage the code to: (delete the space)

#include<stdio.h>
#include<stdlib.h>
int main(){
    int target,result;
    while(1){
        printf("Please input your target: ");
        scanf("%d",&target);//no space
        if(feof(stdin)){
            break;
        }
        printf("test\n");       
    }
}

it worked

edited Jan 05 '21 at 07:31

Barmar

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asked Jan 05 '21 at 07:27

Test Raw

1

You don't need space before `%d`, since it always skips over whitespace to read a number. – Barmar Jan 05 '21 at 07:30
but scanf("%s",a); saves \n in the caches – Test Raw Jan 05 '21 at 11:49
That's OK. As I said, `%d` skips over whitespace, and `\n` is whitespace. – Barmar Jan 05 '21 at 15:05
what if now it's not %d but %s, then the eof can be detected with space added before %s? – Test Raw Jan 06 '21 at 01:50
`%s` also skips over whitespace to read one word. – Barmar Jan 06 '21 at 04:04
You should check the return value of `scanf()` to tell if it read anything. – Barmar Jan 06 '21 at 04:08
there's reason to add space before %, but I forgot it – Test Raw Jan 06 '21 at 07:08
You need it before certain formats, like `%c` because they don't skip whitespace automatically. See https://stackoverflow.com/questions/20306659/the-program-doesnt-stop-on-scanfc-ch-line-why – Barmar Jan 06 '21 at 15:07
Please don't post images of text; see https://meta.stackoverflow.com/questions/303812/discourage-screenshots-of-code-and-or-errors – tripleee Jan 19 '21 at 07:35

How to input eof(Ctrl+z) while letting the scanf have a space before the specifier to avoid getting previous \n error?

0 Answers0