I know pointer hold address of another variable so pointer can hold location of another variable
location of ptr 0061FF14Code:#include<stdio.h> int main () { int a = 10; int *ptr = &a; printf("location of ptr %p \n", &ptr); int *dptr = &ptr; printf(" dptr hold address of ptr is : %p", dptr); return 0; }
dptr hold address of ptr is : 0061FF14
Pointer can store address of pointer and double pointer can also share address of pointer
what's advantage of double pointer ?
Your code doesn't compile.
> what's advantage of double pointer ?Code:$ gcc foo.c foo.c: In function ‘main’: foo.c:8:21: warning: initialization of ‘int *’ from incompatible pointer type ‘int **’ [-Wincompatible-pointer-types] 8 | int *dptr = &ptr; | ^ $
Allocating a 2D array.
Typically like this.
Code:int **twod = malloc( 10 * sizeof(*twod)); for ( int i = 0 ; i < 10 ; i++ ) twod[i] = malloc( 100 * sizeof(*twod[i]) );
If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
If at first you don't succeed, try writing your phone number on the exam paper.
Two other examples to add to Salem's answer... Let's say I want to make a function which closes a file, using a stream, and want to nullify this "ponter" after closing:
The other is where you want an array of strings. A string, in C, is an array of chars where a pointer points to the first char, Like this:Code:void closefile( FILE **fptr ) { if ( *fptr ) fclose( *fptr ); *fptr = NULL; }
Here "fred" (and the final NUL char) is allocated somewhere in memory and the address to the first element is assigned to str. But what if you want an array of strings?Code:char *str = "fred";
strs points to the first pointer, which points to "fred"... We can use a pointer to a pointer of char to iterate through this array:Code:char *strs[] = { "fred", "was", "here", NULL };
[]sCode:char **p = strs; while ( *p ) puts( *p++ );
Fred
Last edited by flp1969; 01-11-2023 at 04:05 PM.
