What does '**' mean in C?

Question

What does it mean when an object has two asterisks at the beginning?

**variable 

Answer 1

In a declaration, it means it's a pointer to a pointer:

int **x;  // declare x as a pointer to a pointer to an int 

When using it, it deferences it twice:

int x = 1; int *y = &x;  // declare y as a pointer to x int **z = &y;  // declare z as a pointer to y **z = 2;  // sets the thing pointed to (the thing pointed to by z) to 2           // i.e., sets x to 2 

Answer 2

It is pointer to pointer.

For more details you can check: Pointer to pointer

It can be good, for example, for dynamically allocating multidimensional arrays:

Like:

#include <stdlib.h>  int **array; array = malloc(nrows * sizeof(int *)); if(array == NULL) {     fprintf(stderr, "out of memory\n");     exit or return }  for(i = 0; i < nrows; i++) {     array[i] = malloc(ncolumns * sizeof(int));     if(array[i] == NULL)     {         fprintf(stderr, "out of memory\n");         exit or return     } }