[golang learning notes 1.7] functions in golang should be used

defer

In the function , Programmers often create resources （ such as ： Database connection , Locks, etc. ）, In order to execute the function after , Release resources in time ,defer You can use it （ Delay mechanism ）

String commonly used system functions

1. Statistical string length : len(str) ; Return the length of string or array
2. String traversal , At the same time, deal with problems containing Chinese : arr:=[]run(str); Convert string to slice

 Example ：
   str:=" Hello ,abc"
      for i := 0; i <len(str); i++ {
    
        fmt.Printf("i: %c\n", str[i])
      }
 Printout 
i: äi: ½i:  i: åi: ¥i: ½i: ,i: ai: bi: c      
 Because it contains Chinese characters , If you don't convert , The printout will be disordered , It's not what we want 
    str:=" Hello ,abc"
      arr:=[]rune(str)
      for i := 0; i <len(arr); i++ {
    
        fmt.Printf("i: %c ", arr[i])
      }
 Printout 
i:  you  i:  good  i: , i: a i: b i: c        

3. String to integer : strconv.Atoi(str)

  //strconv.Atoi  Yes 2 Return values , One is the value of successful conversion , One is the error return of unsuccessful conversion 
  num,err:=strconv.Atoi("123")
      if err != nil{
    
            fmt.Printf("err: %v\n", err)
      }else{
    
           fmt.Printf("num: %v\n", num)
      }

4. Integer to string : strconv.Itoa(int)
5. String rotation byte: []byte(str)
6. byte Turn the string ：str=string([]byte{97,98,99})
7. Hexadecimal conversion :str=strconv.FormatInt(int64,int);int64 The number to be converted ;int The base number to convert 2,8,10 The result of conversion is the corresponding string
8. Determine whether the string is in another string ：strings.Contains(“hello,world”,“world”) If in Then return to true otherwise false
9. Determine how many strings there are in another string :strings.Count(“hello,world”,“world”) Return the number of contains
10. Case insensitive judgment ：strings.EqualFold(“hello,world”,“world”) return bool type
11. Use case sensitive judgment abc==Abc == Equivalent to all equals
12. Returns the subscript value of the first occurrence of one string in another string ： str:=strings.Index(“hello,world”,“world”) return int type
13. Returns the subscript value of the last occurrence of one string in another string ： str:=strings.LastIndex(“hello,world”,“world”) return int type
14. String substitution ：strings.Replace(str,str2,str3,num)

   // The first parameter is the string that needs to be matched 
   // The second parameter is the replacement string 
   // The third is the string to be replaced 
   // The fourth is if there are multiple strings to replace , Then it represents the quantity to be replaced  -1 Replace for all 
   num:=strings.Replace("hhhhh,world","h"," Beijing ",1)

15. Cut the string into an array of strings according to the specified characters ：strings.Split(“h,h,h,h,h,world”,“,”)

   // according to , Division ; Return string array slice 
   num:=strings.Split("h,h,h,h,h,world",",")
   fmt.Printf("type=%T,num=%v\n", num,num)
    Print the results 
   type=[]string,num=[h h h h h world]

16. Case conversion function of letters in string strings.ToLower(“GO”); Turn lowercase .strings.ToUpper(“go”); Turn capitalization .
17. Remove the spaces on the left and right sides of the string ：strings.TrimSpace(" go ");
18. Remove the specified characters on the left and right sides of the string ：strings.Trim(“!go!”,“!”);
19. Remove the specified character on the left of the string ：strings.TrimLeft(“!go!”,“!”);
20. Remove the specified character on the right of the string ：strings.TrimRight(“!go!”,“!”);
21. Determines whether the string begins with the specified string ：strings.HasPrefix(“https://go.com”,“https”); return bool type
22. Determines whether a string ends with the specified string ：strings.HasSuffix(“GO.jpg”,“jpg”); return bool type
23. Subsequent complement …jpg
24. go Document address ：https://studygolang.com/pkgdoc

Time and date correlation function

1. Initialization time now()

   // Now Return to the current local time 
    now:=time.Now()
    fmt.Printf("now: %v\n", now)

2. year

    now:=time.Now()
    fmt.Printf(" year : %v\n", now.Year())

4. month

    now:=time.Now()
    fmt.Printf(" month : %v\n", now.Month())// English month 
    fmt.Printf(" month : %v\n", int(now.Month()))// Digital month 

6. Japan

    now:=time.Now()
    fmt.Printf(" Japan : %v\n", now.Day())

8. when

    now:=time.Now()
    fmt.Printf(" when : %v\n", now.Hour())

10. branch

    now:=time.Now()
    fmt.Printf(" branch : %v\n", now.Minute())

12. second

    now:=time.Now()
    fmt.Printf(" second : %v\n", now.Second())

13. Format time

   // Now Return to the current local time 
    now:=time.Now()
    // Return the current time in the format of year month day hour minute second 【2006/01/02 15:04:05 Is a fixed value ; immutable 】
    // origin 2006 by Golang Time of birth ,15 It's afternoon 3 spot .
    // Ways to help memory ：1 month 2 Japan 3 spot 4 branch 5 second ,2006 year ,-7 The time zone , Is precisely 1234567.
    //2006/01/02 15/04/05  You can freely combine the return time 
    date:=now.Format("2006-01-02 15:04:05")
    fmt.Printf("date: %v\n", date)

14. Time unit

    Nanosecond  Duration = 1 //1 nanosecond 
    Microsecond          = 1000 * Nanosecond  //1 subtle =1000* nanosecond 
    Millisecond          = 1000 * Microsecond //1 millisecond =1000*1 subtle 
    Second               = 1000 * Millisecond //1 second =1000*1 millisecond 
    Minute               = 60 * Second        //1 minute =60*1 second 
    Hour                 = 60 * Minute        //1 Hours =60*1 minute 

15. Get the timestamp

 // Now Return to the current local time 
    now:=time.Now()
    unix:=now.Unix()
    unixnano:=now.UnixNano()
    fmt.Printf("unix: %v\n", unix)
    fmt.Printf("unixnano: %v\n", unixnano)
    // Print the results 
    // unix: 1658126367
    //unixnano: 1658126367931653600 

Error handling

1. defer,panic,recover have access to defer+recover To handle exceptions

   // Define an anonymous function 
   defer func ()  {
    
        //recover() Function can catch exceptions 
        err:=recover()
        // If an exception is caught, the exception information is output 
        if err !=nil{
    
            fmt.Printf("err: %v\n", err)
        }      
    }()

2. panic Output the error and terminate the program

     panic(" To terminate the program , And output error ")

3. Custom error

package main
import (
	"errors"// Reference package 
	"fmt"
)
func main(){
    
    err:= errors.New(" I made a custom error ")
    fmt.Printf("err: %v\n", err)
}