Taking apart strings in C

Question

I have a string that includes two names and a comma how can i take them apart nd write them to seperate strings.
Example

 char *line="John Smith,Jane Smith";

I am thinking of using sscanf function.

 sscanf(line,"%s,%s",str1,str2);

What should i do?
note: I can change comma to space character.

You may want to give this a look: http://stackoverflow.com/questions/9210528/split-string-with-delimiters-in-c — wjmolina, Jan 02 '14 at 18:04
@JoeDF If that family, then `strtok_r()` (it's not inherently thread-unsafe). — , Jan 02 '14 at 18:07
Don't use `strtok`, it modifies the string. As he's using a string-constant it will invoke undefined behaviour. — Kninnug, Jan 02 '14 at 18:08

score 8 · Accepted Answer · answered Jan 02 '14 at 18:05

8

I am thinking of using sscanf function.

Don't even think about it.

char line[] = "John Smith,Jane Smith";
char *comma = strchr(line, ',');
*comma = 0;
char *firstName = line;
char *secondName = comma + 1;

answered Jan 02 '14 at 18:05

1

Actually there is a integer between names => "john Smith,10,Jane Smith". I tought i could manage it if i understand how to do it with only 2 strings. But your answer is a little complex for me (i'm absolute beginner) Do you mind at least a little explaining it to me? – ossobuko Jan 02 '14 at 18:14
2

@OssoBuko Yes. You search for the position of the comma with `strchr()`, then overwrite it with a 0 which terminates the first string. Then you have your first string. Then, you know that the second string starts immediately after the comma, so you grab a pointer to the character after it (`comma + 1`), and there you go, you got the second string too. – Jan 02 '14 at 18:16
@OssoBuko; This a very simple answer if you have some idea about [`strchr`](http://www.tutorialspoint.com/ansi_c/c_strchr.htm). – haccks Jan 02 '14 at 18:58
Sorry mate. I thought i can accept multiple. And i didn't know it was wrong. Sorry to give you a headache. – ossobuko Jan 02 '14 at 19:24

wjmolina · Answer 2 · 2014-01-02T18:51:50.933

-1

Here's how you could do it using strtok:

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

int main() 
{
    // Your string.
    char *line = "John Smith,10,Jane Smith";

    // Let's work with a copy of your string.
    char *line_copy = malloc(1 + strlen(line));
    strcpy(line_copy, line);

    // Get the first person.
    char *pointer = strtok(line_copy, ",");    
    char *first = malloc(1 + strlen(pointer));
    strcpy(first, pointer);

    // Skip the number.
    strtok(NULL, ",");

    // Get the second person.
    pointer = strtok(NULL, ",");    
    char *second = malloc(1 + strlen(pointer));
    strcpy(second, pointer);

    // Print.
    printf("%s\n%s", first, second);

    return 0;
}

edited Jan 02 '14 at 18:51

answered Jan 02 '14 at 18:21

wjmolina

2,625
2
26
35

3

**This is wrong** on so many levels. Firstly, there's an unnecessary copy. You could have just declared `line` as an array. Second, there's no memory allocated for `line_copy`, so `strcpy()`ing onto it leads to undefined behavior (meaning that this could crash or, what's even worse, it could fail silently, causing bigger, hard-to-detect problems elsewhere.) Also, it's better to use `strtok_r()` instead of `strtok()` because the latter is inherently thread-unsafe. – Jan 02 '14 at 18:29
Okay, my code was not suited for industry use alright. I made some changes to it. But when Osso writes a multi-threaded program, I will use `strtok_r`; he said he's an *absolute beginner*. – wjmolina Jan 02 '14 at 18:51
2

@JosuéMolina And that's why it's dangerous to write incorrect code for him. – Jan 02 '14 at 18:52
1

I feel the down-votes and delete request are unnecessarily harsh; my approach was conceptually correct. That it was *unsafe* at first did not deem it *wrong*. Thank you for the constructive criticism, though; I learned something new. – wjmolina Jan 02 '14 at 19:03
By the way, I already removed my downvote. But down voters should leave a comment. – haccks Jan 02 '14 at 19:12

Taking apart strings in C

2 Answers2