Using strtok in c

Question

I need to use strtok to read in a first and last name and seperate it. How can I store the names where I can use them idependently in two seperate char arrays?

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

int main ()
{
  char str[] ="test string.";
  char * test;
  test = strtok (str," ");
  while (test != NULL)
  {
    printf ("%s\n",test);
    test= strtok (NULL, " ");
  }
  return 0;
}

Answer 1

Here is my take at a reasonably simple tokenize helper that

• stores results in a dynamically growing array
• null-terminating the array
• keeps the input string safe (strtok modifies the input string, which is undefined behaviour on a literal char[], at least I think in C99)

To make the code re-entrant, use the non-standard strtok_r

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

char** tokenize(const char* input)
{
    char* str = strdup(input);
    int count = 0;
    int capacity = 10;
    char** result = malloc(capacity*sizeof(*result));

    char* tok=strtok(str," "); 

    while(1)
    {
        if (count >= capacity)
            result = realloc(result, (capacity*=2)*sizeof(*result));

        result[count++] = tok? strdup(tok) : tok;

        if (!tok) break;

        tok=strtok(NULL," ");
    } 

    free(str);
    return result;
}

int main ()
{
    char** tokens = tokenize("test string.");

    char** it;
    for(it=tokens; it && *it; ++it)
    {
        printf("%s\n", *it);
        free(*it);
    }

    free(tokens);
    return 0;
}

Here is a strtok-free reimplementation of that (uses strpbrk instead):

char** tokenize(const char* str)
{
    int count = 0;
    int capacity = 10;
    char** result = malloc(capacity*sizeof(*result));

    const char* e=str;

    if (e) do 
    {
        const char* s=e;
        e=strpbrk(s," ");

        if (count >= capacity)
            result = realloc(result, (capacity*=2)*sizeof(*result));

        result[count++] = e? strndup(s, e-s) : strdup(s);
    } while (e && *(++e));

    if (count >= capacity)
        result = realloc(result, (capacity+=1)*sizeof(*result));
    result[count++] = 0;

    return result;
}

Answer 2

Do you need to store them separately? Two pointers into a modified char array will yield two separate perfectly usable strings.

That is we transform this:

char str[] ="test string.";

Into this:

char str[] ="test\0string.";
             ^     ^
             |     |
char *s1 -----     |
char *s2 -----------

.

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

int main ()
{
  char str[] ="test string.";
  char *firstname = strtok(str, " ");
  char *lastname = strtok(NULL, " ");
  if (!lastname)
    lastname = "";
  printf("%s, %s\n", lastname, firstname);
  return 0;
}