Go Language Basics

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Run: Go run xxx.go

Compile: Go build xxx.go Generate executable file

Program Start: Package Main

Introduction Package: Import "FMT" or import (

"FMT"

"OS"

)

Note: println does not support, printf only supports the output of the% type

Variables and constants:

Declare variables outside of the function: Var a or Var (

a int

b str = "HI"

)

Used in functions:: = declaration, e.g. T: = 10

Note: In go, declaring a variable can not declare a type, it can be inferred automatically by value

Constant definition: const s string = "hi" or const with the Const keyword (

s string = "Hi"

Pi float32 = 3.1415926

)

Array:

var A [5]int defines a value of length 5 as an array of type int

var b [3]int{1, 2, 3} defines a length of 3, and a result of a value of type int is = "[1, 2, 3]

Returns the length of an array using the Len () method

Array slicing operations:

var a [5]int

or a: = [5]int{0,1,2,3,4}

A[2:4] from 2 to 4, excluding 4

A[:4] from 0 to 4, excluding 4

A[2:] from 2 to last including 2

Conditional statements:

If Len (a) = = 5 {....} else {...}              Switch a {case a[0] >0: .... case a[2] = = 2: .... Default: .... }

Note that the switch statement in the go language is not break because Casa in go does not wear

Loop statement:

For I: = 0; I < 5; i++ {} range keyword loop array, map, etc. i: = [3]int{2, 3, 4} for a, V: = Range I {fmt. Println (a) fmt. Println (v)} Dead loop: for {}

Map

Package mainimport "FMT"       func main () {    m  := make (map[string]int)  //use make to create an empty map                         m["One"]  = 1    m["] = 2    m[" "three"] = 3                          fmt. Println (m)  //output  map[three:3 two:2 one:1]  (the order may not be the same at run time)     fmt. Println (Len (m))  //output  3                         v := m["] //" value from map      fmt. Println (v)  //  output  2                         delete (M,   "    fmt"). Println (m)  //output  map[three:3 one:1]                         m1 := map[string ]int{"One": 1,  "one" and ": 2, " "three":  3}    fmt. PRINTLN (M1)  //output  map[two:2 three:3 one:1]  (sequence may not be the same at run time)                           for key, val := range m1{        fmt. Printf ("%s => %d \n",  key, val)         /* Output: (may be different in order at run time)             three =>  3            one => 1             two => 2*/    }}

Pointer

var i int= 1var pInt *int= &i//output: I=1 pint=0xf8400371b0 *pint=1fmt. Printf ("i=%d\tpint=%p\t*pint=%d\n", I, PInt, *pint) *pint = 2//output: i=2 pint=0xf8400371b0 *pint =2fmt. Printf ("i=%d\tpint=%p\t*pint=%d\n", I, pInt, *pint) i = 3//output: i=3 pint=0xf8400371b0 *PINT=3FM t.printf ("i=%d\tpint=%p\t*pint=%d\n", I, PInt, *pint)

Go has two mechanisms for allocating memory, namely the built-in function new and make. They do things differently, they apply different types, which can cause confusion, but the rules are simple.

Memory allocation

New is a built-in function that allocates memory, but unlike the work of new in other languages with the same name, it simply zeroed out the memory instead of initializing the memory. New (t) assigns a zero-value storage space and returns the address, which is a value of type *t, to a project of type T. In the terms of go, it returns a pointer to the newly assigned 0 value of type T.

The purpose of the make (T, args) function differs from new (t). It is used only to create slices, maps, and Chan (message Pipelines) and returns an initialized (not 0) instance of type T (not *t). This difference arises because these three types are essentially references to data structures that must be initialized before they are used. For example, a slice is a descriptor with three items of content, including pointers, lengths, and capacities that point to data (inside an array), and the slice value is nil until the three items are initialized. For slices, mappings, and channels, make initializes its internal data structure and prepares the values that will be used. Such as:

The following code assigns an integer array with a length of 10, a capacity of 100, and a slice that returns the first 10 arrays

Make ([]int, 10, 100)

以下示例说明了new和make的不同。

VarP *[]int = new ([]int)//Allocate memory for the tile structure; *p = nil; rarely use varv []int = make ([]int, 10)//Slice v now is a reference to a new array with 10 integers//unnecessarily complicates the problem *[]int: var p = new ([]int) fmt. PRINTLN (p)//output: &[]*p = make ([]int, Ten, ten) fmt. PRINTLN (p)//output: &[0 0 0 0 0 0 0 0 0 0]fmt. Println ((*P) [2])//output: 0//Customary usage: V: = make ([]int) fmt. Println (v)//output: [0 0 0 0 0 0 0 0 0 0]

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