Pointer Modification via Double Indirection

Snippet

Pointer Modification via Double Indirection

To change the address a pointer in the caller's scope points to, you must pass a pointer to that pointer (double indirection). This allows functions to update external pointers, such as during memory reallocation.

snippet.c
c
#include <stdlib.h>
 
void reallocate_buffer(int **ptr, int new_size) {
    *ptr = realloc(*ptr, new_size * sizeof(int));
}
 
int main() {
    int *buf = malloc(5 * sizeof(int));
    reallocate_buffer(&buf, 10);
    free(buf);
    return 0;
}

Breakdown

int **ptr

Parameter representing a pointer to an integer pointer.

*ptr = realloc(...);

Dereferences the double pointer once to update the original pointer's address.

Previous snippet Next snippet

More Intermediate C exercises →

From your library

Pointer Modification via Double Indirection

Related