C - split string into an array of strings

Question

I'm not completely sure how to do this in C:

char* curToken = strtok(string, ";");
//curToken = "ls -l" we will say
//I need a array of strings containing "ls", "-l", and NULL for execvp()

How would I go about doing this?

Answer 1

Since you've already looked into strtok just continue down the same path and split your string using space (' ') as a delimiter, then use something as realloc to increase the size of the array containing the elements to be passed to execvp.

See the below example, but keep in mind that strtok will modify the string passed to it. If you don't want this to happen you are required to make a copy of the original string, using strcpy or similar function.

char    str[]= "ls -l";
char ** res  = NULL;
char *  p    = strtok (str, " ");
int n_spaces = 0, i;


/* split string and append tokens to 'res' */

while (p) {
  res = realloc (res, sizeof (char*) * ++n_spaces);

  if (res == NULL)
    exit (-1); /* memory allocation failed */

  res[n_spaces-1] = p;

  p = strtok (NULL, " ");
}

/* realloc one extra element for the last NULL */

res = realloc (res, sizeof (char*) * (n_spaces+1));
res[n_spaces] = 0;

/* print the result */

for (i = 0; i < (n_spaces+1); ++i)
  printf ("res[%d] = %s\n", i, res[i]);

/* free the memory allocated */

free (res);

res[0] = ls
res[1] = -l
res[2] = (null)

Answer 2

Here is an example of how to use strtok borrowed from MSDN.

And the relevant bits, you need to call it multiple times. The token char* is the part you would stuff into an array (you can figure that part out).

char string[] = "A string\tof ,,tokens\nand some  more tokens";
char seps[]   = " ,\t\n";
char *token;

int main( void )
{
    printf( "Tokens:\n" );
    /* Establish string and get the first token: */
    token = strtok( string, seps );
    while( token != NULL )
    {
        /* While there are tokens in "string" */
        printf( " %s\n", token );
        /* Get next token: */
        token = strtok( NULL, seps );
    }
}