package main

import "fmt"

func main()  {
    var a int = 10
    //每个变量都有两层含义，变量的内存和变量的地址
    fmt.Printf("a = %d\n", a) //变量的内存 10
    fmt.Printf("a = %v\n", &a) //变量的地址 0xc042060080

    //保存某个变量的地址，需要指针类型， *int保存int的地址， **int保存*int的地址
    //声明（定义），定义只是特殊的声明
    //定义一个变量p,类型为*int
    var p *int
    p = &a
    fmt.Printf("p = %v, &a = %v\n", p, &a)
    *p = 666 //*p操作的不是p的内存，是p指向的内存（其实就是a）
    fmt.Printf("*p = %v, a = %v\n", *p, a)
}

GOROOT=C:\Go #gosetup
GOPATH=E:\go\develop #gosetup
C:\Go\bin\go.exe build -i -o C:\Users\baylor\AppData\Local\Temp\___go_build__go.exe E:/awesomeProject01/指针的基本操作.go #gosetup
"C:\Program Files\JetBrains\GoLand 2018.1.5\bin\runnerw.exe" C:\Users\baylor\AppData\Local\Temp\___go_build__go.exe #gosetup
a = 10
a = 0xc042060080
p = 0xc042060080, &a = 0xc042060080
*p = 666, a = 666

package main

import "fmt"

func main()  {
    var p *int
    p = nil
    fmt.Printf("p = %v\n", p)

    *p = 666 //这个就是错误的，因为它没有正确的指向内存地址
    fmt.Printf("*p = %v\n", *p)
}

GOROOT=C:\Go #gosetup
GOPATH=E:\go\develop #gosetup
C:\Go\bin\go.exe build -i -o C:\Users\baylor\AppData\Local\Temp\___go_build__go.exe E:/awesomeProject01/不要操作没有合法指向的内存.go #gosetup
"C:\Program Files\JetBrains\GoLand 2018.1.5\bin\runnerw.exe" C:\Users\baylor\AppData\Local\Temp\___go_build__go.exe #gosetup
p = <nil>
panic: runtime error: invalid memory address or nil pointer dereference
[signal 0xc0000005 code=0x1 addr=0x0 pc=0x48ce1c]

goroutine 1 [running]:
main.main()
    E:/awesomeProject01/不要操作没有合法指向的内存.go:10 +0x7c

var a int
p = &a
*p = 666
fmt.Printf("*p = %v\n", *p)

p = <nil>
*p = 666