# 26. Pointers

### Pointers 

Pointers is is type of variable in Go. Instead of string a value type, pointer stores address of another variable. Pointer points to address of another variable in Go. To get address of variable, we use `&` operator. To get value that pointer points to, we use `*` operator.

{% code title="main.go" %}

```go
a := 10
b := &a
fmt.Printf("Value of a is %d \n", a)
fmt.Printf("Address of a is %v\n", &a)
fmt.Printf("Value at pointer location is %v\n", *b)
```

{% endcode %}

### Pointer Type

Like we can declare variables to hold different types of values in Go, we can also declare pointer that holds address of different Go types. Variable `intP` is pointer to `int` type while `floatP` is pointer to `float64` type. Similar to value types, we can not assign pointer of type X to pointer of type Y.

{% code title="main.go" %}

```go
var intP *int
var floatP *float64
fmt.Println(intP, floatP)
```

{% endcode %}

### Pointer to structure

It is common to use Pointers with struct in Go. Since it is common use case, for de-referencing (getting value out of pointer) Go does not require us to use asterisk `(*)` symbol. Instead of  `(*myLocation).street` we can use `myLocation.street`

{% code title="main.go" %}

```go

type location struct {
	street  string
	city    string
	pincode int
}

myLocation := &location{
	street:  "Xyz",
	city:    "Pune",
	pincode: 444101,
}

fmt.Printf("I live on %s street, %s city with %d code\n",
	myLocation.street, myLocation.city, myLocation.pincode)
```

{% endcode %}

### Sharing Data

Main use of pointers is to share data between function calls. Pointers when used efficiently help us increase system performance by sharing data instead of making a fresh copy every time between function calls. `updateLocation` function accepts pointer to `location` type and it can update `myLocation` variable value using pointer.

{% code title="main.go" %}

```go

type location struct {
	street  string
	city    string
	pincode int
}
func main() {
	myLocation := &location{
		street:  "Xyz",
		city:    "Pune",
		pincode: 444101,
	}

	fmt.Printf("I live on %s street, %s city with %d code\n",
		myLocation.street, myLocation.city, myLocation.pincode)

	// sharing data
	updateLocation(myLocation)

	fmt.Printf("I live on %s street, %s city with %d code\n",
		myLocation.street, myLocation.city, myLocation.pincode)
}

func updateLocation(loc *location) {
	loc.city = "Mumbai"
}
```

{% endcode %}

### Blog Resources

{% embed url="<https://www.ardanlabs.com/blog/2013/07/understanding-pointers-and-memory.html>" %}

{% embed url="<https://www.ardanlabs.com/blog/2014/12/using-pointers-in-go.html>" %}

{% embed url="<https://www.ardanlabs.com/blog/2017/05/language-mechanics-on-stacks-and-pointers.html>" %}


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://book.codewithgo.com/pointers.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.