golang学习之指针、内存分配

func pointer_test() {
//空指针，输出为nil
var p *int
fmt.Printf("p: %v\n", p)
//指向局部变量，变量值初始为0
var i int
p = &i
fmt.Printf("p: %v,%v\n", p, *p)
//通过指针修改变量数值
*p = 8
fmt.Printf("p: %v,%v\n", p, *p)
//数组的初始化及输出
m := [3]int{3, 4, 5}
fmt.Printf("m:%v--%v,%v,%v\n", m, m[0], m[1], m[2])
//指针数组的初始化及输出
//j, k, l := 3, 4, 5
//x := [3]*int{&j, &k, &l}
x := [3]*int{&m[0], &m[1], &m[2]}
fmt.Printf("x:%v,%v,%v\n", x[0], x[1], x[2])
fmt.Printf("*x:%v,%v,%v\n", *x[0], *x[1], *x[2])

var n [3]*int
n = x
fmt.Printf("n:%v,%v,%v\n", n[0], n[1], n[2])
//指向数组的指针，也即二级指针的使用
y := []*[3]*int{&x}
fmt.Printf("y:%v,%v\n", y, y[0])
fmt.Printf("*y[0]:%v\n", *y[0])
fmt.Printf("*y[][]:%v,%v,%v\n", *y[0][0], *y[0][1], *y[0][2])
/*
*X            ->    v
[3]X        ->    [v0][v1][v2]
[]X            ->    [v0]...[vi]
[3]*X        ->    [p0][p1][p2]
|   |   |
j   k   l
[]*[3]*X    ->    [n0]...[ni]
| ... |
[p0]->j
[p1]->k
[p2]->l
*/
}

type Student struct {
name  string
id    int
score uint
}

func memery_test() {
//new分配出来的数据是指针形式
p := new(Student)
p.name = "China"
p.id = 63333
p.score = 99
fmt.Println(*p)
//var定义的变量是数值形式
var st Student
st.name = "Chinese"
st.id = 666333
st.score = 100
fmt.Println(st)
//make分配slice、map和channel的空间，并且返回的不是指针
var ptr *[]Student
fmt.Println(ptr)     //ptr == nil
ptr = new([]Student) //指向一个空的slice
fmt.Println(ptr)
*ptr = make([]Student, 3, 100)
fmt.Println(ptr)
stu := []Student{{"China", 3333, 66}, {"Chinese", 4444, 77}, {"Chince", 5555, 88}}
fmt.Println(stu)
}