golang中map每次输出时顺序都不一致，在某些情况下甚至需要按顺序输出map。那么如何做到顺序输出呢？

1. map每次输出结果都不一致

package main

import (
    "fmt"
    "sort"
)

func main() {
    mp := make(map[string]string)
    mp["beijing"] = "beijing"
    mp["tianjin"] = "tianjin"
    mp["shanghai"] = "shanghai"
    mp["chongqing"] = "chongqing"
    mp["guangdong"] = "guangzhou"
    mp["jiangsu"] = "nanjing"
    mp["zhejiang"] = "hanzhou"

    for key, value := range mp {
        fmt.Println(key, " ----> ", value)
    }

    fmt.Println("second output")
    for key, value := range mp {
        fmt.Println(key, " ----> ", value)
    }
}

两次输出打印结果不一致，如下输出结果为：

chongqing ----> chongqing
guangdong ----> guangzhou
jiangsu ----> nanjing
zhejiang ----> hanzhou
beijing ----> beijing
tianjin ----> tianjin
shanghai ----> shanghai
second output
chongqing ----> chongqing
guangdong ----> guangzhou
jiangsu ----> nanjing
zhejiang ----> hanzhou
beijing ----> beijing
tianjin ----> tianjin
shanghai ----> shanghai

2. 顺序输出map
   实现顺序输出map，首先需要获取map中所有key，然后将key排序，最后按排序后key输出map。

package main

import (
    "fmt"
    "sort"
)

func main() {
    mp := make(map[string]string)
    mp["beijing"] = "beijing"
    mp["tianjin"] = "tianjin"
    mp["shanghai"] = "shanghai"
    mp["chongqing"] = "chongqing"
    mp["guangdong"] = "guangzhou"
    mp["jiangsu"] = "nanjing"
    mp["zhejiang"] = "hanzhou"

    for key, value := range mp {
        fmt.Println(key, " ----> ", value)
    }

    fmt.Println("second output")
    for key, value := range mp {
        fmt.Println(key, " ----> ", value)
    }

    fmt.Println("sort output")
    keys := []string{}
    for key, _ := range mp {
        keys = append(keys, key)
    }
    sort.Strings(keys)
    for _, key := range keys {
        fmt.Println(key, " ----> ", mp[key])
    }
    return
}

排序后输出结果为按key排序结果

chongqing ----> chongqing
guangdong ----> guangzhou
jiangsu ----> nanjing
zhejiang ----> hanzhou
beijing ----> beijing
tianjin ----> tianjin
shanghai ----> shanghai
second output
chongqing ----> chongqing
guangdong ----> guangzhou
jiangsu ----> nanjing
zhejiang ----> hanzhou
beijing ----> beijing
tianjin ----> tianjin
shanghai ----> shanghai
sort output
beijing ----> beijing
chongqing ----> chongqing
guangdong ----> guangzhou
jiangsu ----> nanjing
shanghai ----> shanghai
tianjin ----> tianjin
zhejiang ----> hanzhou