Get the beginning of a string until a given char

Question

I know that is a simple question but I couldn't find the answer.

I have this string:

"M1[r2][r3]"

I want to get only the "M1", I'm looking for something like strchr() a function that get the string and a char to stop at.

@CIsForCookies I think `"M1[r2][r3]"` is the content of the string. — Federico klez Culloca, Aug 23 '17 at 06:49
@Federico klez Culloca Like you said, "M1[r2][r3]" is the string — Elon Salfati, Aug 23 '17 at 06:50
Show some other strings and which part of them you want, otherwise the answer is `printf("M1");`. — Yunnosch, Aug 23 '17 at 06:53
Try this: [https://stackoverflow.com/questions/2114377/strings-in-c-how-to-get-substring](https://stackoverflow.com/questions/2114377/strings-in-c-how-to-get-substring) Or this: [https://stackoverflow.com/questions/4214314/get-a-substring-of-a-char](https://stackoverflow.com/questions/4214314/get-a-substring-of-a-char) Hope this helps. — Nahid Islam Shaiket, Aug 23 '17 at 06:54
Use [strtok()](https://linux.die.net/man/3/strtok) to tokenize strings based on a separator like `"["`. — Andre Kampling, Aug 23 '17 at 06:54
@AndreKampling I was writing this answer and only after that saw your comment :( — CIsForCookies, Aug 23 '17 at 06:56
The question is unclear. Is the code the declaration or the string itself? If it is the string, then why can't you use strchr as you propose yourself? — Lundin, Aug 23 '17 at 06:57
I thought this isn't a "write my code" site? The question is very poor quality. — Weather Vane, Aug 23 '17 at 06:59
`char id[8]; sscanf("M1[r2][r3]", " %7[^[]", id);` (`int len = 0; sscanf("M1[r2][r3]", " %7[^[][%n", id, &len);`) — BLUEPIXY, Aug 23 '17 at 07:25

CIsForCookies · Accepted Answer · 2017-08-23T08:57:26.850

9

What about using strtok and "[" as a delimiter?

#include <string.h> /* for strtok */
#include <stdio.h>  /* for printf */
int main()
{
    char str[] = "M1[r2][r3]"; // str will be modified by strtok
    const char deli[] = "[";   // deli could also be declared as [2] or as const char *. Take your pick...
    char *token;

    token = strtok(str, deli); // can also call strtok(str, "["); and not use variable deli at all
    printf("%s", token);       // printf("%s", str); will print the same result

    /* OUTPUT: M1 */

    return 0;    
}

edited Aug 23 '17 at 08:57

answered Aug 23 '17 at 06:55

CIsForCookies

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You should mention that `strtok()` changes the input buffer so that printing `str` will be `"M1"` too because every separator will be replaced by a null terminator. Further no `[2]` is needed use just `[]`. – Andre Kampling Aug 23 '17 at 06:57
I don't get why this answer get downvotes. Yes it isn't a "write the code for me" site but the answer isn't wrong or lacks in quality. I would say if somebody isn't comfortable with an answer to such a question he/she shouldn't upvote but also not downvote. – Andre Kampling Aug 23 '17 at 07:02
1

I agree that `[]` will be ok, but why not use `[2]`? I think of it as a reminder (especially for beginners) that "[" is a string literal that has 2 `char` – CIsForCookies Aug 23 '17 at 07:03
1

@ClsForCookies: Ah I didn't saw it that way :D. I was just thinking don't repeat yourself. – Andre Kampling Aug 23 '17 at 07:04
@AndreKampling it is usually considered [**unhelpful**](https://meta.stackoverflow.com/questions/334822/how-do-i-ask-and-answer-homework-questions) to supply a pat answer to "gimme the code" questions. – Weather Vane Aug 23 '17 at 07:05
1

I hope I'm not overstepping my bounds, but from my experience, when I was doing my first steps here at SO, these were the answers that were most helpful for me. I got to learn about new functions and how someone else would achieve my question goal. If the OP wasn't a noob here, my answer would be different – CIsForCookies Aug 23 '17 at 07:07
1

@CIsForCookies nice answer, +1, but please include the headers needed, some users might not be aware of them (although they can see it in the ref, but...). – gsamaras Aug 23 '17 at 08:41

score 2 · Answer 2 · answered Aug 23 '17 at 06:57

Use strtok() and the character to stop (a delimeter, in your case [) like this:

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

int main ()
{
  char str[] ="M1[r2][r3]";
  printf ("Getting M1 from \"%s\":\n",str);
  strtok (str,"[");
  if (str != NULL)
    printf ("%s\n",str);
  return 0;
}

Output:

Getting M1 from "M1[r2][r3]":
M1

However, if you know the length of the substring, you should see Get a substring of a char*.

chux - Reinstate Monica · Answer 3 · 2022-05-03T18:22:44.807

2

something like strchr() a function that get the string and a char to stop at.

If only a printing of the sub-string is needed, use strcspn() which finds the offset when '[' first occurs, (or the end if not found). This does not alter the source string.

const char *s = "M1[r2][r3]";
printf("%.*s\n", (int) strcspn(s, "["), s);

Output

M1

edited May 03 '22 at 18:22

answered Aug 23 '17 at 13:01

chux - Reinstate Monica

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Beautiful function. – jav May 03 '22 at 18:20
@jav Thanks - but it did have the wrong type - answer amended. – chux - Reinstate Monica May 03 '22 at 18:23

gsamaras · Answer 4 · 2017-08-23T07:56:49.550

1

Use sscanf() like this:

char subStr[3];
sscanf("M1[r2][r3]", " %2[^[]", subStr);

where [^[] means a character except [ and 2 guards the length of the string written into the substring (it's equal to subStr's size - 1, so that space for the NULL terminator is available).

as BLUEPIXY suggested.

edited Aug 23 '17 at 07:56

answered Aug 23 '17 at 07:39

gsamaras

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Get the beginning of a string until a given char

4 Answers4