Pointers and References

people who have a Java programming background like me, may be have a feeling that it is easy to understand the concept of pointers and references , but have a hard time to remember & and * 's operations.

[ & ] - a memory address marker

Computer store data in memory , and each memory has an address.

package  main

import  (
 "fmt"
)

func  main()  {
    var data int  =  5;
    fmt.Printf("Memory Address: %p and Data: %d ",  &data ,  data);
}

[output]
Memory Address: 0x10328000 and Data: 5 
Program exited.

So & is a address marker.

[ * ] - a pointer marker

If we wanted to store the address of a piece of data into a variable instead of using it directly as above , we can do it this way ,

package  main

import(
  "fmt"
)

func  main()  {
  var i int = 7
  var p *int
  p =  &i

  fmt.Println("i : " , i)
  fmt.Println("memory address of i : ", &i)
  fmt.Println("p : " , p)
  fmt.Println("*p : " , *p)
}

[output]
i :  7
memory address of i :  0x10328000
p :  0x10328000
*p :  7

Program exited.

So what is a pointer ?

A pointer look like "special data type" in which the memory address of another value is stored.

var p *int

We called p a pointer ( an integer pointer ) , and *int a "special data type" , because it looks nothing like any builtin data type - bool , int8 , int16 ...etc , but it is in a position of type of a variable declaration ( l don't know whether it is a TYPE internally ).

What about *p ? the asterisk in front of p , which make *p equal to 7 ? Oh .. we called the asterisk a pointer dereference operator .

p ( &i ) is a pointer , and *p is the data it pointing to.

But can we get the address back by using **p or *( p ) , like we do maths , (-5)(-5) = +25 ?

No , it is not the right syntax.

package  main

import(
  "fmt"
)

func  main()  {
  var i int = 7
  var p *int
  p =  &i

  fmt.Println(" **p : " , **p)       // both cannot be compile
  fmt.Println(" *(*p) : " , *(*p))
}

[output]
prog.go:12: invalid indirect of *p (type int)
prog.go:13: invalid indirect of *p (type int)
 [process exited with non-zero status]

Program exited.

Show Me More Pointers ?

Using new() to create pointer :

package main

import "fmt"

func main() {
    c := new(int)
    fmt.Println("c -> ", c)
}

[output]
c ->  0x10328000

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