Split string with delimiters in C

Question

How do I write a function to split and return an array for a string with delimiters in the C programming language?

char* str = \"JAN,FEB,MAR,APR,MAY,JUN,JUL,         


        

Answer 1

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.