In C, what does a variable declaration with two asterisks (**) mean?

Question

I am working with C and I'm a bit rusty. I am aware that * has three uses:

1. Declaring a pointer.
2. Dereferencing a pointer.
3. Multiplication

However, what does it mean when there are two asterisks (**) before a variable declaration:

char **aPointer = ... 

Thanks,

Scott

Answer 1

It declares a pointer to a char pointer.

The usage of such a pointer would be to do such things like:

void setCharPointerToX(char ** character) {    *character = "x"; //using the dereference operator (*) to get the value that character points to (in this case a char pointer } char *y; setCharPointerToX(&y); //using the address-of (&) operator here printf("%s", y); //x 

Here's another example:

char *original = "awesomeness"; char **pointer_to_original = &original; (*pointer_to_original) = "is awesome"; printf("%s", original); //is awesome 

Use of ** with arrays:

char** array = malloc(sizeof(*array) * 2); //2 elements  (*array) = "Hey"; //equivalent to array[0] *(array + 1) = "There";  //array[1]  printf("%s", array[1]); //outputs There 

The [] operator on arrays does essentially pointer arithmetic on the front pointer, so, the way array[1] would be evaluated is as follows:

array[1] == *(array + 1); 

This is one of the reasons why array indices start from 0, because:

array[0] == *(array + 0) == *(array);