Golang Slice Small note

1-Slice initialization

1Func Printslice (S []int) {2Fmt. Printf ("len=%d cap=%d underlying array:%p,%v\n", Len (s), Cap (s), S, s)3 }4 5 func sliceinit () {6 7     varS1 []int//declares S1, and does not initialize, at this time S1 is nil slice, no underlying array is assigned8     ifS1 = =Nil {9Fmt. Println ("S1 is nil")Ten     } One  AS2: = []int{} -     ifS2 = =Nil { -Fmt. Println ("S2 is nil") the     } -  -S3: = Make ([]int,0) -     ifS3 = =Nil { +Fmt. Println ("S3 is nil!") -     } +  A Printslice (S1) at printslice (S2) - Printslice (S3) - } - Func Main () { - Sliceinit () -}

Out:

 is Nillen=0 cap=0 underlying array:0x0, []len=0 cap=0 underlying array:0x55c988, []len=0 cap=0 underlying array:  0x55c988, []

2 Slice length and capacity

The length of the slice is the number of elements it contains.

The capacity of a slice is the number of its first element starting at the end of its underlying array element

Func Main () {s:= []int{2,3,5,7, One, -} printslice (s)//Slice the Slice to give it zero length.s = s[:0] Printslice (s)//Extend its length.s = s[:4] Printslice (s)//Drop its first and the values.s = s[2:] Printslice (s)}

Out:

len=6cap=6Underlying array:0xc04200a2a0, [2 3 5 7  One  -]len=0cap=6Underlying array:0xc04200a2a0, []len=4cap=6Underlying array:0xc04200a2a0, [2 3 5 7]len=2cap=4Underlying array:0xc04200a2b0, [5 7]

3 Assignment and parameter transfer

1 func Slicet () {2Arraya: = [5]int{ -, $, -, -, -}3Fmt. Printf ("Arraya:%p,%v\n", Arraya, Arraya)4Fmt. Printf ("Arraya:%p,%v\n", &Arraya, Arraya)5 6Fmt. Printf ("Arraya:%p,%v\n", &arraya[0], Arraya)7Fmt. Printf ("Arraya:%p,%v\n", &arraya[1], Arraya)8Fmt. Printf ("Arraya:%p,%v\n", &arraya[2], Arraya)9Fmt. Printf ("Arraya:%p,%v\n", &arraya[3], Arraya)TenFmt. Printf ("Arraya:%p,%v\n", &arraya[4], Arraya) One  ASlice: = arraya[1:3:4] -Fmt. Printf ("Slice:%p,%v\n", slice, slice) -Fmt. Printf ("Slice:%p,%v\n", &slice[0], slice) theFmt. Printf ("Slice:%p,%v\n", &slice[1], slice) -  -slice[0] =0 -Fmt. Printf ("Slice:%p,%v\n", slice, slice) +Fmt. Printf ("Arraya:%p,%v\n", &Arraya, Arraya) -  +}

Out

3Arraya:%!p ([5]int=[ -  $  -  -  -]), [ -  $  -  -  -]4Arraya:0xc04206c030, [ -  $  -  -  -]
6Arraya:0xc04206c030, [ -  $  -  -  -]7Arraya:0xc04206c038, [ -  $  -  -  -]8Arraya:0xc04206c040, [ -  $  -  -  -]9Arraya:0xc04206c048, [ -  $  -  -  -]TenArraya:0xc04206c050, [ -  $  -  -  -]
Slice:0xc04206c038, [ $  -]Slice:0xc04206c038, [ $  -]Slice:0xc04206c040, [ $  -]
 -Slice0xc04206c038, [0  -] +Arraya:0xc04206c030, [ - 0  -  -  -]

The

An array variable represents the entire array, which is not a pointer to the first element (unlike the C-language array) so the array name cannot be printed by%p the address. When an array variable is assigned or passed, the entire array is actually copied. (To avoid copying an array, you can pass a pointer to the array)

6~9

int occupies 8 bytes on 64 machines

12~15

Slice syntax a[Low:high:cap]; CAP indicates tile capacity

The slice name is printed by%p and the address of the underlying array referenced by the slice is output

18~19

Changing the value of a slice element is the corresponding element value of the array to which it is referenced.

1 func Slicet () {2s: = []int{1,2,3,4,5}3Fmt. Printf ("underlying array:%p, slice addr:%p\n", S, &s)4 Changeslice (s)5 FMT. Println (s)6 }7 8Func Changeslice (S []int) {9Fmt. Printf ("underlying array:%p, param slice addr:%p\n", S, &s)Tens[1] = -1 One}

Out:

0xc04206c030 0xc04204a3a0  0xc04206c0300xc04204a400[1 -134 5]

1 func sliceT1 () {2s: = []int{1,2,3,4,5}3Fmt. Printf ("underlying array:%p, slice addr:%p\n", S, &s)4 ChangeSlice1 (s)5 FMT. Println (s)6 }7 8Func ChangeSlice1 (S []int) {9Fmt. Printf ("underlying array:%p, param slice addr:%p\n", S, &s)Tens = Append (S,1) One}

Out:

0xc04200a2a0 0xc0420023e0  0xc04200a2a00xc042002440[12345 ]

When a slice is passed as a function parameter is a value pass, a slice is copied, but the formal parameters and arguments have the same underlying array reference.

More information: https://blog.go-zh.org/go-slices-usage-and-internals

Https://www.jianshu.com/p/030aba2bff41