[Golang] Common verbs of formatting string
在fmt package裡Printf, Fprintf, Fscanf, Scanf，或像是log package裡的Printf, Fatalf， 只要是function名字後面有f的，就能format你的input，以fmt.Printf為例:
fmt.Printf("My name is %s. I am %d years old", "HoMuChen", 30)
//My name is HoMuChen. I am 30 years old
第一個參數將會是最後輸出的字串，不過中間我們可以看到%s、%d的東西，稱之為verb，
verb會被後面的參數取代掉，並且是依照你指定的格式，這篇文章將會分享一寫常用的verb。
Overview
以下為一個常用的verbs表格，依照要format的值的型態做分類，後面再詳細說明:
| category | syntax | description |
|---|---|---|
| general | %v | value in default format |
| %T | type | |
| %% | literal % sign | |
| boolean | %t | true or false |
| interger | %b | binary |
| %o | base 8 | |
| %d | base 10 | |
| %x | base 16 | |
| %X | base 16 with upper-case letters | |
| floating | %e | scientific notation |
| %f | decimal point but no exponent | |
| %g | for large exponents | |
| string | %s | string |
| %q | double quoted string | |
| padding | %10s | width 10 string |
| %-10s | width 10 string left padding | |
| %10d | width 10 digit | |
| %010d | width 10 digit filled with 0 | |
| floating precision | %8f | width 8 floating number |
| %8.2f | width 8 with 2 digit presicion floating number | |
| %.2f | 2 digit presicion floating number |
General
%v: 根據不同的值的型態，預設的格式
| type | format |
|---|---|
| boolean | %t |
| string | %s |
| int | %d |
| float32,float64 | %g |
%T: 值的型態 ```go fmt.Printf("The type of this value is %T", "I am a string") //The type of this value is string
fmt.Printf("The type of this value is %T", true) //The type of this value is bool ```
%%: 真的想要%的時候go fmt.Printf("%v %%", 100) //100 %
Boolean
%t:go fmt.Printf("This is %t", true)
Integer
%b%d%x: base 2, 10, 16go fmt.Printf("base 2: %b, base 10: %d, base 16: %x", 255, 255, 255) //base 2: 11111111, base 10: 255, base 16: ff
Floating point number
-
%e: 科學記號表示 -
%f: 十進位表示，預設顯示到小數點後六位。go fmt.Printf("%f", 123.123456789) //123.123457 -
%g: 小數點後很多位的話，用%g全部顯示出來。go fmt.Printf("%g", 123.123456789) //123.123456789
String
-
%s: 就是字串～ -
%q: 以雙引號括起來的字串，就不需要再額外寫類似\"escape掉。go fmt.Printf("%q", "I am a string") //"I am a string"
Padding
有時我們想要輸出的字串是一樣長度的，可以在前面加上一個數字，代表你想要長度，以下例子:
-
%10s: 寬度為10的字串go users := []string{"David", "Mu", "HoMuChen", "Noname"} for _, user := range users { fmt.Printf("User: %10s does something\n", user) }text User: David does something User: Mu does something User: HoMuChen does something User: Noname does something -
%-10s: 寬度為10的字串，左邊對齊go users := []string{"David", "Mu", "HoMuChen", "Noname"} for _, user := range users { fmt.Printf("User: %-10s does something\n", user) }text User: David does something User: Mu does something User: HoMuChen does something User: Noname does something -
%-7d: 寬度為7的整數，左邊對齊go contentLengths := []int{70, 240, 614, 12345} for _, contentLength := range contentLengths { fmt.Printf("content length: %-7d bytes\n", contentLength) }text content length: 70 bytes content length: 240 bytes content length: 614 bytes content length: 12345 bytes
Floating point number precision
也可以指定浮點數的總長度及小數點後要到第幾位。
-
%10f: 總長度為10的浮點數，小數點後預設為6位，如果需要超過長度10才能表示，還是會超過。go fmt.Printf("response time: %10f ms\n", 25.35) fmt.Printf("response time: %10f ms\n", 125.35) fmt.Printf("response time: %10f ms\n", 2125.11)text response time: 25.350000 ms response time: 125.350000 ms response time: 2125.110000 ms //長度超過9了 -
%.2f: 指定小數點後到第2位。go fmt.Printf("response time: %.2f ms\n", 25.35123) // response time: 25.35 ms -
%10.2f: 總長度為10，且只小數點後兩位go fmt.Printf("response time: %10.2f ms\n", 25.35) fmt.Printf("response time: %10.2f ms\n", 125.35) fmt.Printf("response time: %10.2f ms\n", 2125.11)text response time: 25.35 ms response time: 125.35 ms response time: 2125.11 ms
Summary
在這篇文章記錄了常用的verbs，除了自己忘記可以回來看，也希望能幫助到有需要的人，掰掰～👋
