djg123

 Profile Answers by djg123 

• Sep 4th, 2010

 

Linked list, Tree, Hashing

rashmi nayak

• Sep 10th, 2011

 

int i=10;
int *p;
p=&i;
int **q;
q=&p;
this means a pointer pointing to a pointer which in turn points to an integer.....this is called double pointer....

garima

• Oct 6th, 2011

 

double pointers are useful whenever you have defined user defined pointers in your main function. And you want to change their values from outside the main like in functions other than main. There the use of pointers is must.

jbode

 Profile Answers by jbode Questions by jbode

• Oct 10th, 2011

 

By double pointers I assume you're talking about something like **ptr, as opposed to a simple pointer to a double object.

Multiple levels of indirection show up in the following areas:

1. You want a function to modify a pointer value. To do this, you must pass a pointer to the pointer:

void openAndInit(FILE **stream)
{
*stream = fopen(some_file, "w");
fprintf(*stream, "some initial data");
}

int main(void)
{
FILE *dat;
...
openAndInit(&dat);
...
}

2. We want to dynamically allocate a multi-dimensional array:

int **x;
x = malloc(sizeof *x * ROWS);
if (x)
{
int i;
for (i = 0; i < ROWS; i++)
{
x[i] = malloc(sizeof *x[i] * COLS);
}
}

Those are two uses off the top of my head; they aren't the only ones.