copy an array in c

I have a function, it accepts a char**, what is the quickest and most efficient way of making a local copy of the array in the function scope?

That is, i have , for example:

void funk(char **x){

char **b;

/*How do i make a separate copy of x to b?*/
}

Take pity on me internets, I'm a noob :) Thanks.

need to pass in len of x, then:

char **b = malloc(sizeof(*x) * n)
for (i = 0; i < n; i++) {
  if (!x[i]) b[i] = 0
  else b[i] = strdup(x[i])
}