Split string with delimiters in C

I think strsep is still the best tool for this:

while ((token = strsep(&str, ","))) my_fn(token);

That is literally one line that splits a string.

The extra parentheses are a stylistic element to indicate that we're intentionally testing the result of an assignment, not an equality operator ==.

For that pattern to work, token and str both have type char *. If you started with a string literal, then you'd want to make a copy of it first:

// More general pattern:
const char *my_str_literal = "JAN,FEB,MAR";
char *token, *str, *tofree;

tofree = str = strdup(my_str_literal);  // We own str's memory now.
while ((token = strsep(&str, ","))) my_fn(token);
free(tofree);

If two delimiters appear together in str, you'll get a token value that's the empty string. The value of str is modified in that each delimiter encountered is overwritten with a zero byte - another good reason to copy the string being parsed first.

In a comment, someone suggested that strtok is better than strsep because strtok is more portable. Ubuntu and Mac OS X have strsep; it's safe to guess that other unixy systems do as well. Windows lacks strsep, but it has strbrk which enables this short and sweet strsep replacement:

char *strsep(char **stringp, const char *delim) {
  if (*stringp == NULL) { return NULL; }
  char *token_start = *stringp;
  *stringp = strpbrk(token_start, delim);
  if (*stringp) {
    **stringp = '\0';
    (*stringp)++;
  }
  return token_start;
}

Here is a good explanation of strsep vs strtok. The pros and cons may be judged subjectively; however, I think it's a telling sign that strsep was designed as a replacement for strtok.

You can use the strtok() function to split a string (and specify the delimiter to use). Note that strtok() will modify the string passed into it. If the original string is required elsewhere make a copy of it and pass the copy to strtok().

EDIT:

Example (note it does not handle consecutive delimiters, "JAN,,,FEB,MAR" for example):

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

char** str_split(char* a_str, const char a_delim)
{
    char** result    = 0;
    size_t count     = 0;
    char* tmp        = a_str;
    char* last_comma = 0;
    char delim[2];
    delim[0] = a_delim;
    delim[1] = 0;

    /* Count how many elements will be extracted. */
    while (*tmp)
    {
        if (a_delim == *tmp)
        {
            count++;
            last_comma = tmp;
        }
        tmp++;
    }

    /* Add space for trailing token. */
    count += last_comma < (a_str + strlen(a_str) - 1);

    /* Add space for terminating null string so caller
       knows where the list of returned strings ends. */
    count++;

    result = malloc(sizeof(char*) * count);

    if (result)
    {
        size_t idx  = 0;
        char* token = strtok(a_str, delim);

        while (token)
        {
            assert(idx < count);
            *(result + idx++) = strdup(token);
            token = strtok(0, delim);
        }
        assert(idx == count - 1);
        *(result + idx) = 0;
    }

    return result;
}

int main()
{
    char months[] = "JAN,FEB,MAR,APR,MAY,JUN,JUL,AUG,SEP,OCT,NOV,DEC";
    char** tokens;

    printf("months=[%s]\n\n", months);

    tokens = str_split(months, ',');

    if (tokens)
    {
        int i;
        for (i = 0; *(tokens + i); i++)
        {
            printf("month=[%s]\n", *(tokens + i));
            free(*(tokens + i));
        }
        printf("\n");
        free(tokens);
    }

    return 0;
}

Output:

$ ./main.exe
months=[JAN,FEB,MAR,APR,MAY,JUN,JUL,AUG,SEP,OCT,NOV,DEC]

month=[JAN]
month=[FEB]
month=[MAR]
month=[APR]
month=[MAY]
month=[JUN]
month=[JUL]
month=[AUG]
month=[SEP]
month=[OCT]
month=[NOV]
month=[DEC]

String tokenizer this code should put you in the right direction.

int main(void) {
  char st[] ="Where there is will, there is a way.";
  char *ch;
  ch = strtok(st, " ");
  while (ch != NULL) {
  printf("%s\n", ch);
  ch = strtok(NULL, " ,");
  }
  getch();
  return 0;
}