Lesson 37: Pointers Part 4: Pointers and Functions

Using pointers in functions enables us to perform Call by Reference and pass complex data structures efficiently.

1. Achieving Call by Reference (The Swap Function)

To allow a function to modify variables declared outside its scope, we pass the addresses of those variables.

c #include <stdio.h>

void swap(int *x, int *y) { int temp = *x; // Store the value pointed to by x *x = *y; // Change the value at address x to the value at address y *y = temp; // Change the value at address y to the original x value }

int main() { int a = 5, b = 10; printf("Before swap: a=%d, b=%d\n", a, b);

// Pass the addresses
swap(&a, &b);

printf("After swap: a=%d, b=%d\n", a, b); 
return 0;

}

2. Returning Pointers from Functions

Functions can return a pointer (an address).

Warning: Never return the address of a local (automatic) variable, as that memory is deallocated when the function exits, resulting in a dangling pointer.

If you must return a pointer, it should point to:

1. A global variable.
2. A static local variable.
3. Dynamically allocated memory (covered next).
4. Memory passed into the function as an argument.