sscanf not working space from stdin

Question

I have some issue with sscanf function in C.

My program

#include <stdio.h>
#include <stdlib.h>

int main(){
    char str[50];
    int y=0, x=0;

    printf("Insert string: ");
    scanf("%s", str);
    sscanf(str, "%d %d", &x, &y);
    printf("x:%d  y:%d\n",x,y);
    return 0;
}

Input

10 20

Output

x:10  y:0

I also tried

sscanf(str, "%d%d", &x, &y);

and

sscanf(str, "%d%*[ \n\t]%d", &x, &y);

but the output is the same.

The strange thing is that when I try

#include <stdio.h>
#include <stdlib.h>

int main(){
    char str[] = "10 20";
    int y=0, x=0;

    sscanf(str, "%d %d", &x, &y);
    printf("x:%d  y:%d\n",x,y);
    return 0;
}

my output is x:10 y:20

Answer 1

That's not because sscanf fault, it's that scanf ignore whitespace.

As pointed out many times (How do you allow spaces to be entered using scanf?), you should use fgets instead to get string input.

So replacing scanf("%s", str); with the line below would work:

fgets( str, 50, stdin );