How to split a string to 2 strings in C

Question

I was wondering how you could take 1 string, split it into 2 with a delimiter, such as space, and assign the 2 parts to 2 separate strings. I've tried using strtok() but to no avail.

Solution 1

#include <string.h>

char *token;
char line[] = "SEVERAL WORDS";
char *search = " ";


// Token will point to "SEVERAL".
token = strtok(line, search);


// Token will point to "WORDS".
token = strtok(NULL, search);

---

Update

Note that on some operating systems, strtok man page mentions:

This interface is obsoleted by strsep(3).

An example with strsep is shown below:

char* token;
char* string;
char* tofree;

string = strdup("abc,def,ghi");

if (string != NULL) {

  tofree = string;

  while ((token = strsep(&string, ",")) != NULL)
  {
    printf("%s\n", token);
  }

  free(tofree);
}

Solution 2

For purposes such as this, I tend to use strtok_r() instead of strtok().

For example ...

int main (void) {
char str[128];
char *ptr;

strcpy (str, "123456 789asdf");
strtok_r (str, " ", &ptr);

printf ("'%s'  '%s'\n", str, ptr);
return 0;
}

This will output ...

'123456' '789asdf'

If more delimiters are needed, then loop.

Hope this helps.

Solution 3

char *line = strdup("user name"); // don't do char *line = "user name"; see Note

char *first_part = strtok(line, " "); //first_part points to "user"
char *sec_part = strtok(NULL, " ");   //sec_part points to "name"

Note: strtok modifies the string, so don't hand it a pointer to string literal.

Solution 4

You can use strtok() for that Example: it works for me

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

int main ()
{
    char str[] ="- This, a sample string.";
    char * pch;
    printf ("Splitting string \"%s\" into tokens:\n",str);
    pch = strtok (str," ,.-");
    while (pch != NULL)
    {
        printf ("%s\n",pch);
        pch = strtok (NULL, " ,.-");
    }
    return 0;
}

Solution 5

If you have a char array allocated you can simply put a '\0' wherever you want. Then point a new char * pointer to the location just after the newly inserted '\0'.

This will destroy your original string though depending on where you put the '\0'

View more solutions

Comments

[Drew Delano]

Show us your strtok() attempt.

[John Bode]

strtok() modifies its input, so using it on a string literal is bad juju (a.k.a undefined behavior).

[John Bode]

Looks good, except the second strtok() call is using a different delimiter.

[ereOn]

Yep. I forgot to mention that. Thanks.

[Drew Delano]

@ereOn: Perhaps you missed the point. Your example is passing a pointer to a string literal, therefore strtok() will be modifying the string literal and invoking UB.

[thecoshman]

What's the difference betwen strtok_r() and strtok()?

[ereOn]

My point was to demonstrate the basic use of strtok(). Well, I admit that using string literals in this situation is a bad pratice and should be avoided. Fun fact: if you look at cplusplus.com/reference/clibrary/cstring/strtok you can see the same "mistake" in the example.

[Drew Delano]

I think if you change char *line = "SEVERAL WORDS" to char line[] = "SEVERAL WORDS", you're all set.

[ereOn]

If this is true, I just learned something. I thought those two instructions had the same meaning. My bad.

[David Thornley]

@ereOn: Pointers and arrays are different things in C, until you sneeze near an array, and then it turns into a pointer. That's how the array size expression sizeof(arr)/sizeof(arr[0]) works.

[ereOn]

strtok_r() is the reentrant version of strtok(). More about reentrancy here: en.wikipedia.org/wiki/Reentrant_%28subroutine%29

[pmg]

strtok() is obsoleted? WOW! strsep() is not even Standard C.

[Bitterblue]

@ereOn Is it normal that strtok and strsep are throwing error signals ? Is there a way to avoid errors ? None of the code above worked without errors for me.

[ereOn]

@mini-me: I never heard of error signals using those functions. You probably should ask your own question (referring to this one, if it is relevant).