Pointers

Misc

Distinguishing Between Void Pointers and Char Pointers

Void Pointers	Character Pointers
Truly generic. Can point to any data type	Points to characters or bytes (given a byte is just an unsigned char)
Cannot be dereferenced directly since the data type it points to is unknown	Can be dereferenced directly
Requires type casting before dereferencing	Used for byte-level operations.

Pass by Value and Pass by Reference

Pass by value

Advantages	Disadvantages
Easy to understand - you can just pass copies, nothing to deference.	Performance overhead - A big object like a struct to be copied will be time and memory intensive.
Safe - Original data won’t be modified by the called function	Short reach(Lack of direct access) - Called functions can only modify local copies. This can be a good thing too.

Pass by reference

Advantages	Disadvantages
Efficiency - You just pass an address, it can point to a gigantic structure, not a problem.	Can be complex to understand - You have to dereference the pointer to get the value.
Direct access - can modify data outside the called function. This trick allows us to return multiple values from a function.

Associativity

pointers have unary operators therfore associativity is right to left

int *p;
int x = 5.2;
p = &x;
printf("%d", *(int*)p);

here if we had

printf("%f", (int*)*p);

It would result in a compilation error because of associativity rule.

Another case of associativity:

printf("%u", (int*)p++);

This will result in an error because the compiler will try to add 1 to the pointer first and then typecast it to an integer pointer. To avoid this, we can use parentheses to enforce the correct order of operations:

printf("%u", ((int*)p)++);

This will add 1 to the pointer p first and then typecast the result to an integer pointer.

*(arr + 1) = arr[1]

int *a[5] mean “a” is an array of 5 integer pointers.

Note

#include <stdio.h>

int main() {
    int *ptr[3], i , iA[]={5,10,15}, iB[]={1,2,3}, iC[]={2,4,6};
    ptr[0]=iA; ptr[1]=iB; ptr[2]=iC;
    for(i=0; i<3 ; i++){
        printf("iA[%d]: address=%p data=%d", i, ptr[0]+i, *(ptr[0]+i));
        printf("iB[%d]: address=%p data=%d", i, ptr[0]+i, *(ptr[0]+i));
        printf("iC[%d]: address=%p data=%d", i, ptr[0]+i, *(ptr[0]+i));
    }

    return 0;
}

Resources to refer to: