GeezerVison

Go supports pointers, allowing you to pass references to values and records within your program.

package main

import "fmt"

We’ll show how pointers work in contrast to values with 2 functions: zeroval and zeroptr. zeroval has an int parameter, so arguments will be passed to it by value. zeroval will get a copy of ival distinct from the one in the calling function.

func zeroval(ival int) {
    ival = 0
}

zeroptr in contrast has an *int parameter, meaning that it takes an int pointer. The *iptr code in the function body then dereferences the pointer from its memory address to the current value at that address. Assigning a value to a dereferenced pointer changes the value at the referenced address.

func zeroptr(iptr *int) {
    *iptr = 0
}

func main() {
    i := 1
    fmt.Println("initial:", i)

    zeroval(i)
    fmt.Println("zeroval:", i)

The &i syntax gives the memory address of i, i.e. a pointer to i.

    zeroptr(&i)
    fmt.Println("zeroptr:", i)

Pointers can be printed too.

    fmt.Println("pointer:", &i)

A new pointer to a value can be created with the builtin function new.

    p := new(42)
    fmt.Println("value at *p:", *p)
    zeroptr(p)
    fmt.Println("value at *p:", *p)
}

zeroval doesn’t change the i in main, but zeroptr does because it has a reference to the memory address for that variable.

$ go run pointers.go
initial: 1
zeroval: 1
zeroptr: 0
pointer: 0x42131100
value at *p: 42
value at *p: 0