Getting to Know Pointers in Golang

We know that sending a variable to a function can be a parameter or a pointer. This pointer is usually a data allocation with a certain address. An example can be seen in the program below.

package main

import "fmt"

func zero(xPtr *int) {
	*xPtr = 0
}

func main() {
	x := 5
	zero(&x)
	fmt.Println(x)
}

Use * and &

In Go, a pointer is represented using the character * (asterisk) followed by the type of the value being stored. In the null function xPtr is a pointer to int.

* is also used to “dereference” pointer variables. Pointer dereference gives us access to the value that the pointer points to. When we write *xPtr = 0 we are saying “store int 0 in the memory location that xPtr refers to”. If we try xPtr = 0 instead we will get a compiler error because xPtr is not int but rather *int, which can only be given another *int.

Finally we use the & operator to find the variable address. &x returns *int (pointer to int) because x is an int. This is what allows us to modify the original variable. &x in main and xPtr in null refer to the same memory location.

Another way to get the pointer is to use the built-in new function:

package main

import "fmt"

func one(xPtr *int) {
	*xPtr = 1
}
func main() {
	xPtr := new(int)
	one(xPtr)
	fmt.Println(*xPtr)
}

In some programming languages there is a significant difference between using new and &, with great care required to ultimately remove anything created with new. Go is not like that, because it has garbage collection, that is, memory is cleaned automatically when there is no longer anything to refer to it.