Sequentially truncate string if delimiter is found.
  If string is not NULL, the function scans string for the first occurrence of any character included in delimiters. If it is found, the function overwrites the delimiter in string by a null-character and returns a pointer to the token, i.e. the part of the scanned string previous to the delimiter.
  After a first call to strtok, the function may be called with NULL as string parameter, and it will follow by where the last call to strtok found a delimiter.
  delimiters may vary from a call to another.

Parameters.

string

Null-terminated string to scan.

separator

Null-terminated string containing the separators.

Return Value.
  A pointer to the last token found in string.   NULL is returned when there are no more tokens to be found.

Portability.
  Defined in ANSI-C.

Example.

/* strtok example */
#include <stdio.h>
#include <string.h>

/* strtok example */
#include 
#include 

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

See also.
  strcspn, strspn