Pointers in Go

• A pointer stores the memory address of a variable.
• & → Gets the address of a variable.
• * → Dereferences a pointer (accesses the value).

var x int = 10
ptr := &x   // ptr holds the address of x
fmt.Println(*ptr) // 10 (dereferenced value)

Why Use Pointers?

✔ Modify original values inside functions
✔ Avoid copying large structs (better performance)
✔ Share data across functions

Common Pitfalls

❌ Nil pointer dereference → Runtime panic

var ptr *int
fmt.Println(*ptr) // panic: nil pointer dereference

❌ Modifying copies instead of originals

func update(x int) { x = 20 } // Doesn’t modify original
func updatePtr(x *int) { *x = 20 } // Works

FAQ

1. What is a pointer in Go?

A: A variable that stores the memory address of another variable.

var x int = 10
ptr := &x  // ptr holds the address of x

2. Why use pointers?

✔ Modify original values inside functions
✔ Avoid copying large structs (better performance)
✔ Share data across functions

3. What’s the zero value of a pointer?

A: nil (uninitialized pointers point to nothing).

4. How to check for nil pointers?

if ptr != nil {
    fmt.Println(*ptr) // Safe dereference
}

5. What’s the difference between *T and &T?

• *T: Type declaration (pointer to type T).
• &T: Operator to get the address of a variable.

6. Can you have a pointer to a pointer?

A: Yes (double pointers):

var x int = 10
ptr := &x
pptr := &ptr  // **int
fmt.Println(**pptr) // 10

7. When to use pointers vs values in function arguments?

• Pointers: To modify the original value or for large structs.
• Values: For small, immutable data or read-only operations.

8. What happens if you dereference a nil pointer?

A: Runtime panic:

var ptr *int
fmt.Println(*ptr) // panic: nil pointer dereference

9. How do pointers work with slices and maps?

• Slices/maps are already reference-like (no need for pointers usually).
• But pointers are needed if you want to modify the slice/map header itself.

10. What’s the output of this code?

func update(x *int) { *x = 20 }
func main() {
    x := 10
    update(&x)
    fmt.Println(x) // ?
}

A: 20 (pointer modifies the original value).

Key Points to Remember

1. & → Address-of operator.
2. * → Dereference operator (or pointer type declaration).
3. Rule: *T is a pointer to type T.
4. Always check for nil before dereferencing!