C - sscanf not working

Question

I'm trying to extract a string and an integer out of a string using sscanf:

#include<stdio.h>

int main()
{
    char Command[20] = "command:3";
    char Keyword[20];
    int Context;

    sscanf(Command, "%s:%d", Keyword, &Context);

    printf("Keyword:%s\n",Keyword);
    printf("Context:%d",Context);

    getch();
    return 0;
}

But this gives me the output:

Keyword:command:3
Context:1971293397

I'm expecting this ouput:

Keyword:command
Context:3

Why does sscanf behaves like this? Thanks in advance you for your help!

Is there a good reason you don't check the result of `sscanf`? — Maxim Egorushkin, Oct 25 '11 at 09:15

score 21 · Accepted Answer · answered Oct 25 '11 at 09:11

21

sscanf expects the %s tokens to be whitespace delimited (tab, space, newline), so you'd have to have a space between the string and the :

for an ugly looking hack you can try:

sscanf(Command, "%[^:]:%d", Keyword, &Context);

which will force the token to not match the colon.

answered Oct 25 '11 at 09:11

John Weldon

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You mean, there's no way I can use ":" as delimiter? – kazinix Oct 25 '11 at 09:12
So not possible to extract the string and an integeer from "command:3"? – kazinix Oct 25 '11 at 09:15
yes, it is: `sscanf(Command, "%7s:%d", Keyword, &Context);` on the other end, this accepts only commands that are 7 characters long. – Ferenc Deak Oct 25 '11 at 09:16
@John, it's working, and I wonder why :D Can you please explain? Thank you so much. – kazinix Oct 25 '11 at 09:19
the contents of the [] indicate characters to match. if the first character in the [] is ^ it tells the function to match everything *except* the characters in the [] – John Weldon Oct 25 '11 at 09:25
@kfmfe04 It doesn't. – Jan 18 '18 at 11:35

score 8 · Answer 2 · answered Oct 25 '11 at 09:27

If you aren't particular about using sscanf, you could always use strtok, since what you want is to tokenize your string.

    char Command[20] = "command:3";

    char* key;
    int val;

    key = strtok(Command, ":");
    val = atoi(strtok(NULL, ":"));

    printf("Keyword:%s\n",key);
    printf("Context:%d\n",val);

This is much more readable, in my opinion.

score 3 · Answer 3 · answered Oct 25 '11 at 09:22

use a %[ convention here. see the manual page of scanf: http://linux.die.net/man/3/scanf

#include <stdio.h>

int main()
{
    char *s = "command:3";
    char s1[0xff];
    int d;
    sscanf(s, "%[^:]:%d", s1, &d);
    printf("here: %s:%d\n", s1, d);
    return 0;
}

which gives "here:command:3" as its output.

C - sscanf not working

3 Answers3