pointer to pointer ( double pointer )

• to make it simple to to receive the address of the another pointer variable the double pointer will come into picture
• http://www.thegeekstuff.com/2012/01/advanced-c-pointers/
• for pointer array you can refer
•  http://www.netospgm.blogspot.in/2014/08/pointer-array-and-its-advantage.html
• http://publib.boulder.ibm.com/infocenter/macxhelp/v6v81/index.jsp?topic=%2Fcom.ibm.vacpp6m.doc%2Flanguage%2Fref%2Fclrc03example_prog_pointers.htm

• example program(passing single pointer to function and chaning the single pointer value in the called functi
• 
  

root@selvakumar-Lenovo-B460e:/C_pgms/double_pointer# cat dptr.c 
#include<stdio.h>
int func(int **pointer_to_pointer);
int main()
{
 int a=10;
 int *ptr,**pptr;
 ptr = (int *) &a;
 pptr = &ptr;
 printf("\nvalue in *ptr =%d\n",*ptr);
 func(&ptr);
 printf("\nvalue in *ptr after func call =%d\n",*ptr);
 return 0;
}
int func(int **pointer_to_pointer) 
// to hold the address of another pointer
{
 printf("\nvalue in pointer_to_pointer =%d\n",**pointer_to_pointer);
 **pointer_to_pointer = 20;
}
root@selvakumar-Lenovo-B460e:/C_pgms/double_pointer# gcc dptr.c 
root@selvakumar-Lenovo-B460e:/C_pgms/double_pointer# ./a.out 

value in *ptr =10

value in pointer_to_pointer =10

value in *ptr after func call =20
root@selvakumar-Lenovo-B460e:/C_pgms/double_pointer# 

Passing double pointer to function:

Like others have said, you need to take a pointer to pointer to pointer in your init function. This is how the initialize function changes:

void initialize(double ***A, int r, int c)
{
   *A = (double **)malloc(sizeof(double *)*r);
   for(int i = 0; i< r; i++) {
        (*A)[i] = (double *)malloc(sizeof(double) *c);
        for(int j = 0; j < c; j++) {
            (*A)[i][j] = 0.0;
        }
   }
}

And main will be:

int main()
{
    double **A;
    initialize(&A, 10, 10);
}




Ref:https://stackoverflow.com/questions/4339201/c-how-to-pass-a-double-pointer-to-a-function

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