为什么指针会产生错误“无效的间接”？

Question

p is a pointer which points to array arr, we can get array arr by using *p, but why can not get second element by using *p[2]?

It will cause an error :

invalid indirect of p[1] (type int)

The following code:

arr := [4]int{1,2,3,4}
var p *[4]int = &arr
fmt.Println(p)     // output &[1 2 3 4]
fmt.Println(*p)    // output [1 2 3 4]
fmt.Println(p[1])  // output 2
fmt.Println(*p[1]) //generate an error:invalid indirect of p[1] (type int)

Answer 1

Because *p[1] means *(p[1]). And (p[1]) is an int which you can't dereference.

Use parenthesis to dereference the pointer first, and index the result:

fmt.Println((*p)[1])

Also note that p[1] without parenthesis and dereferencing is allowed and works because p is a pointer to an array, and quoting from Spec: Index expressions:

For a of pointer to array type:

• a[x] is shorthand for (*a)[x]

But note that the same is not allowed for pointer to slice types.