介紹

宣告

方式1

方式2

初始化

添加/修改

洗掉

查找

記憶體

遍歷

for range

排序

全部代碼

截圖

參考

介紹

參考型別
Map 是一種無序的鍵值對的集合，Map 最重要的一點是通過 key 來快速檢索資料，key 類似于索引，指向資料的值，
Map 是使用 hash 表來實作的，
鍵不能重復
map自動擴容

宣告

方式1

var map 變數名 map[key_type]value_type

代碼

	var m map[string]string

方式2

make函式

func make(Type, size IntegerType) Type

內建函式make分配并初始化一個型別為切片、映射、或通道的物件，其第一個實參為型別，而非值，make的回傳型別與其引數相同，而非指向它的指標，其具體結果取決于具體的型別：

映射：初始分配的創建取決于size，但產生的映射長度為0，size可以省略，這種情況下就會分配一個小的起始大小，

map的鍵必須是可以通過運算子== 來比較的資料型別，int、布爾、string、或包含前面的struct、陣列等

宣告時直接make

var 變數名 = make(map[key_type][value_type])

代碼

	var m1 = make(map[string]string,5)

初始化

key:value形式，添加到花括號中，

代碼

	m2 := map[string]string{"野王":"趙云"}

添加/修改

map[key] = value形式，沒有會添加，有了會覆寫，

代碼

	m1["上官"] = "言為心聲"
	m1["婉兒"] = "字為心畫"
	m2["野王"] = "老虎"
	m2["上單"] = "呂布"

洗掉

func delete(m map[Type]Type1, key Type)

內建函式delete按照指定的鍵將元素從映射中洗掉，若m為nil或無此元素，delete不進行操作，

	delete(m1,"上官")

清空：重新make，沒有其他語言類似clear的函式

查找

m[key]回傳值和是否存在（bool型別）

	val,flag := m2["野王"]
	if flag{
		fmt.Println("野王:",val)
	}

記憶體

查看原始碼

src->runtime->map.go

// A header for a Go map.
type hmap struct {
	// Note: the format of the hmap is also encoded in cmd/compile/internal/gc/reflect.go.
	// Make sure this stays in sync with the compiler's definition.
	count     int // # live cells == size of map.  Must be first (used by len() builtin)
	flags     uint8
	B         uint8  // log_2 of # of buckets (can hold up to loadFactor * 2^B items)
	noverflow uint16 // approximate number of overflow buckets; see incrnoverflow for details
	hash0     uint32 // hash seed

	buckets    unsafe.Pointer // array of 2^B Buckets. may be nil if count==0.
	oldbuckets unsafe.Pointer // previous bucket array of half the size, non-nil only when growing
	nevacuate  uintptr        // progress counter for evacuation (buckets less than this have been evacuated)

	extra *mapextra // optional fields
}

// A bucket for a Go map.
type bmap struct {
	// tophash generally contains the top byte of the hash value
	// for each key in this bucket. If tophash[0] < minTopHash,
	// tophash[0] is a bucket evacuation state instead.
	tophash [bucketCnt]uint8
	// Followed by bucketCnt keys and then bucketCnt elems.
	// NOTE: packing all the keys together and then all the elems together makes the
	// code a bit more complicated than alternating key/elem/key/elem/... but it allows
	// us to eliminate padding which would be needed for, e.g., map[int64]int8.
	// Followed by an overflow pointer.
}

是哈希表實作，拉鏈法解決沖突，

遍歷

for range

	for key,value := range m2{
		fmt.Println(key,value)
	}

排序

對key排序，然后遍歷

	m2["野王2"] = "趙云"
	m2["野王3"] = "瑪瑪哈哈"
	m2["上單2"] = "馬超"
	keys := []string{}
	for key,_ := range m2{
		keys = append(keys, key)
	}
	sort.Strings(keys)
	fmt.Println("上單和野王排行榜:")
	for _,key := range keys{
		fmt.Println(key,m2[key])
	}

注意：不是執行緒安全的，如果需要執行緒安全的，可以使用sync/Map，等到包的那一節會詳細展開，

全部代碼

package main

import (
	"fmt"
	"sort"
)

func main() {
	//-------------宣告---------------
	var m map[string]string
	//----------宣告并分配空間------
	var m1 = make(map[string]string,5)
	m2 := map[string]string{"野王":"趙云"}
	//---------添加和修改---------------
	m1["上官"] = "言為心聲"
	m1["婉兒"] = "字為心畫"
	m2["野王"] = "老虎"
	m2["上單"] = "呂布"
	fmt.Println("m m1 m2:",m,m1,m2)
	//----------洗掉-------------------
	delete(m1,"上官")
	fmt.Println("m1:",m1)
	//------------查找-------------
	val,flag := m2["野王"]
	if flag{
		fmt.Println("野王:",val)
	}
	//------------遍歷-------------
	for key,value := range m2{
		fmt.Println(key,value)
	}
    //------------排序------------
	m2["野王2"] = "趙云"
	m2["野王3"] = "瑪瑪哈哈"
	m2["上單2"] = "馬超"
	keys := []string{}
	for key,_ := range m2{
		keys = append(keys, key)
	}
	sort.Strings(keys)
	fmt.Println("上單和野王排行榜:")
	for _,key := range keys{
		fmt.Println(key,m2[key])
	}
}