golang字符串截取的两种方式

打印出时间,发现采用lastIndex要比split的方式要快一些.

直接上代码

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package main

import (
"log"
"strings"
	"time"
)

func main()  {
	name := "a.txh.doc"
	t := time.Now()
	for i:=0;i<1000;i++{
		split(name)
	}
	log.Println(time.Now().Sub(t))

	t1 := time.Now()
	for i:=0;i<1000;i++{
		lastIndex(name)
	}
	log.Println(time.Now().Sub(t1))
}
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func split(name string) (int,string){
	result := strings.Split(name, ".")
	resultLen := len(result)
	if resultLen < 2 {
		return 200, "0"
	}
	filenameWithSuffixToLower := strings.ToLower(result[resultLen-1])
	switch filenameWithSuffixToLower {
	case "pdf":
		return 200, "1"
	case "doc", "docx":
		return 200, "2"
	case "xls", "xlsx":
		return 200, "3"
	case "ppt", "pptx", "pps":
		return 200, "4"
	case "png", "gif", "jpeg", "jpg", "bmp":
		return 200, "5"
	case "txt":
		return 200, "6"
	default:
		return 200, "0"
	}
}

func lastIndex(name string) (int,string){
	index := strings.LastIndex(name,".")
	if index < 0 {
		return 200, "0"
	}
	result := name[index+1:]
	filenameWithSuffixToLower := strings.ToLower(result)
	switch filenameWithSuffixToLower {
	case "pdf":
		return 200, "1"
	case "doc", "docx":
		return 200, "2"
	case "xls", "xlsx":
		return 200, "3"
	case "ppt", "pptx", "pps":
		return 200, "4"
	case "png", "gif", "jpeg", "jpg", "bmp":
		return 200, "5"
	case "txt":
		return 200, "6"
	default:
		return 200, "0"
	}
}

split内部的实现可看到源码(如下),内部也是去做的for循环字符串截取分隔,所以lastIndex直接获取到索引,直接截取:

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// Generic split: splits after each instance of sep,
// including sepSave bytes of sep in the subarrays.
func genSplit(s, sep string, sepSave, n int) []string {
	if n == 0 {
		return nil
	}
	if sep == "" {
		return explode(s, n)
	}
	if n < 0 {
		n = Count(s, sep) + 1
	}
	c := sep[0]
	start := 0
	a := make([]string, n)
	na := 0
	for i := 0; i+len(sep) <= len(s) && na+1 < n; i++ {
		if s[i] == c && (len(sep) == 1 || s[i:i+len(sep)] == sep) {
			a[na] = s[start : i+sepSave]
			na++
			start = i + len(sep)
			i += len(sep) - 1
		}
	}
	a[na] = s[start:]
	return a[0 : na+1]
}

golang
golang, 小技巧