Pointer Functions

• Pointers can also store the address of a function. This allows functions to be passed as arguments to other functions.

Syntax:

returnType (*functionPointer)(parameterTypes);

Example:

void printHello() {
    cout << "Hello, World!";
}

int main() {
    void (*funcPtr)() = printHello;  // Function pointer
    funcPtr();  // Call the function through the pointer
    return 0;
}

• Function pointers allow for callback mechanisms, where functions can be passed and invoked later.

Pointers as Function Arguments (Pass by Reference):

• Instead of passing a copy of a variable, you can pass a pointer to a function, allowing the function to modify the original variable (pass by reference).

void increment(int *ptr) {
    (*ptr)++;  // Dereference pointer and increment value
}

int main() {
    int a = 10;
    increment(&a);  // Pass address of `a`
    cout << a;  // Outputs 11
    return 0;
}

• Using pointers in function arguments allows for efficient manipulation of arrays and large data structures, as only the address is passed, not the actual data.

More Examples:

void print(int *p) {
    cout << *p << endl;                 // Will print the value pointed by p
}

void update(int *p) {
   // p = p + 1;
   // cout << "inside "<< p <<endl;
   *p = *p + 1;                         // Increments the value pointed by p by 1
}

int getSum(int *arr, int n) {
    cout << endl << "Size : " << sizeof(arr) << endl; // 8 (size of pointer on 64-bit system)
    int sum = 0;
    for(int i=0;i<n;i++) {
        sum += arr[i];                  // Adds n elements starting from arr
    }
    return sum;
}

int main() {
    int value = 5;
    int *p = &value;

    // print(p);
    cout << " Before " << *p << endl;    // Before 5
    update(p);
    cout << " After " << *p << endl;     // After 6

    int arr[6] = {1,2,3,4,5,8};

    cout << "Sum is " << getSum(arr+3, 3) << endl ; //
    // Inside getSum:
    // Size : 8
    // sum = 4 (arr[3]) + 5 (arr[4]) + 8 (arr[5]) = 17
    // Output: Sum is 17
}