C language: How to get the remaining string after using strtok() once

Question

My string is "A,B,C,D,E"
And the separator is ","
How can I get the remaining string after doing strtok() once, that is "B,C,D,E"

char a[] = "A,B,C,D,E";
char * separator = ",";
char * b = strtok(a,separator);
printf("a: %s\n", a);
printf("b: %s\n", b);

The output is:
a: A
b: A

But how to get the result
a: B,C,D,E
b: A

Thanks.

Don't think `strtok()` does that. – Rohan Nov 01 '13 at 10:00 — Rohan, Nov 01 '13 at 10:00

score 27 · Answer 1 · answered Nov 01 '13 at 10:17

27

You can vary the set of delimiters, so simply pass an empty string:

char a[] = "A,B,C,D,E";
char * separator = ",";
char * b = strtok(a, separator);
printf("b: %s\n", b);
char * c = strtok(NULL, "");
printf("c: %s\n", c);

answered Nov 01 '13 at 10:17

Neil

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2

**Passing no delimiter is the way to go!** In my case, I have used `strtok` more than once, and at some point I needed the remainder. So **not** using `strtok` was not a solution. Neither summing characters because I was `toking` on space, and it could contain a variable number of consecutive spaces, etc. – Paschalis Jun 23 '15 at 13:35

unwind · Answer 2 · 2016-07-11T10:50:10.373

12

Don't use strtok() for this, since that's not what it's for.

Use strchr() to find the first separator, and go from there:

char a[] = "A,B,C,D,E";
const char separator = ',';
char * const sep_at = strchr(a, separator);
if(sep_at != NULL)
{
  *sep_at = '\0'; /* overwrite first separator, creating two strings. */
  printf("first part: '%s'\nsecond part: '%s'\n", a, sep_at + 1);
}

edited Jul 11 '16 at 10:50

answered Nov 01 '13 at 10:01

unwind

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Very cleaver solution! – Federico Ponzi Jul 10 '16 at 19:37

alk · Answer 3 · 2013-11-01T10:18:40.730

Try this:

char a[] = "A,B,C,D,E";
char * end_of_a = a + strlen(a); /* Memorise the end of s. */
char * separator = ",";
char * b = strtok(a, separator);
printf("a: %s\n", a);
printf("b: %s\n", b);

/* There might be some more tokenising here, assigning its result to b. */

if (NULL != b)
{
  b = strtok(NULL, separator);
}

if (NULL != b)
{ /* Get reference to and print remainder: */
  char * end_of_b = b + strlen(b);

  if (end_of_b != end_of_a) /* Test whether there really needs to be something, 
                        will say tokenising did not already reached the end of a, 
                        which however is not the case for this example.  */
  {
    char * remainder = end_of_b + 1;
    printf("remainder: `%s`\n", remainder);
  }   
}

score 1 · Answer 4 · answered Nov 01 '13 at 10:09

strtok remembers the last string it worked with and where it ended. To get the next string, call it again with NULL as first argument.

char a[] = "A,B,C,D,E";
const char *separator = ",";
char *b = strtok(a, separator);
while (b) {
    printf("element: %s\n", b);
    b = strtok(NULL, separator);
}

Note: This is not thread safe.

score 0 · Answer 5 · answered Nov 01 '13 at 10:02

0

If using strtok is not a requirement, you can use strchr instead since the separator is a single character:

char a[] = "A,B,C,D,E";
char *sep = strchr(a, ',');
*sep = '\0';
puts(a);
puts(sep + 1);

answered Nov 01 '13 at 10:02

Fred Foo

355,277
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score 0 · Answer 6 · answered Nov 01 '13 at 10:04

0

printf("a: %s\n", a+1+strlen(b));

Try this

answered Nov 01 '13 at 10:04

nav_jan

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Please see *larsmans* comments to *dasblinkenlight*'s answer on this approach. It as well applies to your answer. – alk Nov 01 '13 at 10:09

score 0 · Answer 7 · answered Mar 09 '21 at 12:34

There's much better ways to work with ip addresses, but this is a practical example of needing to change delimeter at a certain point during execution from '.' to '/'.

struct Ip split_ip_by_octet(char ip_string[]) {

    struct Ip ip;
    char * value_before_delimeter = strtok(ip_string, "."); // N. 

    if (value_before_delimeter != NULL) {
        sscanf(value_before_delimeter, "%d", &ip.octet_1);
        value_before_delimeter = strtok(NULL, ".");        // n.N.

        sscanf(value_before_delimeter, "%d", &ip.octet_2);
        value_before_delimeter = strtok(NULL, ".");        // n.n.N.n/n

        sscanf(value_before_delimeter, "%d", &ip.octet_3);
        value_before_delimeter = strtok(NULL, "/");        // n.n.n.N/n

        sscanf(value_before_delimeter, "%d", &ip.octet_4);
        value_before_delimeter = strtok(NULL, "");         // n.n.n.n/N

        sscanf(value_before_delimeter, "%d", &ip.mask);
    }
    return ip; 
}

C language: How to get the remaining string after using strtok() once

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