inside while loop used fflush does not work

Question

#include<stdio.h>
int main(){
    char arr[20];
    int a;
    int count=0;
    while(1){
        printf("enter string with space:");
        fflush(stdin);
        scanf("%[^\n]%*c", arr);
        printf("enter integer:");
        scanf("%d",&a);
        count++;
        if(count==4){
            break;
        }
    }
}

I want to read string with space and I have to use this code. I wrote this in while loop and I want to read string and after integer number and it does not work.

Output:

enter string with space:hey hey

enter integer:159

enter string with space:enter integer:

But output should be:

enter string with space:hey hey

enter integer:159

enter string with space:.... heyy

enter integer: 1235

Why do you "_have to_ us this code_"? If that is the code you must use, how can we help? The code you need will necessarily be different. — Clifford, May 22 '21 at 06:42
Please take a look at [Using fflush(stdin)](https://stackoverflow.com/q/2979209) — mediocrevegetable1, May 22 '21 at 06:47
@mediocrevegetable1 I could not see the solution to this here. and I was just told to use this code while read string with space — jack1919, May 22 '21 at 06:49
I typed incorrectly while editing the question, now I've edited it. — jack1919, May 22 '21 at 06:57
You still state that you _must_ use this code; implying that it cannot be changed. — Clifford, May 22 '21 at 07:01
Also you read the integer _after_ the string; not "_string and after integer_". — Clifford, May 22 '21 at 07:07

score 2 · Answer 1 · answered May 22 '21 at 06:57

2

fflush() is not defined input streams such as stdin. You will find that it works on Microsoft's C library, but not GNU.

Your scanf() call is incorrect. The first format specifier is incorrect, and you have no format specifier for string ;

scanf("%*[^\n]%*c") ;

will discard any remaining buffered characters to the end of the line inclusive. It accepts no input - it is not clear what string is or what you want to do with it. I'd suggest using a separate input call for that, for clarity.

Another somewhat less arcane solution is:

int c ;
while ((c = getchar()) != '\n' && c != EOF) { }

answered May 22 '21 at 06:57

Clifford

88,407
13
85
165

I was just told to use fflush code while read string with space and I typed incorrectly something while editing the question, now I've edited it. – jack1919 May 22 '21 at 06:59
@jack1919 : But it is still incorrect in exactly the same way, changing `string` to `arr` does not change that. You have omitted the `*` in `%*[^\n]`. Never transcribe your code manually, copy & paste it for accuracy. Otherwise you are asking about code we cannot see while posting misleading code. – Clifford May 22 '21 at 07:04
Note this is an answer to the original question before it was edited, and also to the question implied in the title. It does not address the whole question as it now stands. – Clifford May 22 '21 at 07:11

score 0 · Accepted Answer · answered May 22 '21 at 07:01

0

enter string with space:enter integer:

This happens because after you enter integer input, \n is still left in the stream. %[ does not skip leading whitespace unlike most other format specifiers. Change scanf("%[^\n]%*c", arr); to scanf(" %[^\n]%*c", arr); so it manually skips the leading whitespace before taking input.

As for fflush(stdin), that is undefined behavior (see Using fflush(stdin)). @Clifford already provides two nice solutions to that issue.

answered May 22 '21 at 07:01

mediocrevegetable1

4,086
1
11
33

1

indeed; my answer is to the original question, not the edited question - which is a different question that it originally appeared. – Clifford May 22 '21 at 07:10

inside while loop used fflush does not work

2 Answers2