go 🐹

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fmt formatting opts

When using functions from the fmt package, there are some formatting codes one must use to print out values to the console. Eg.:

package main

type User struct {
  Id   int
  Name string
}

func main() {
  user := User{Id: 123, Name: "Joel"}

  fmt.Println("User: %+v", user) // => {Id:123 Username:joeljuca}
}

At first sight, the question that comes to mind is: WTF is %+v?

Below I list these notations and WTF each of them are.

General

• %v: the value in a default format when printing structs
  • %+v: same as %v but adds field names
• %#v: a Go-syntax representation of the value
• %T: a Go-syntax representation of the type of the value
• %%: a literal percent sign; consumes no value

Boolean

• %t: the word true or false

Integer

• %b: base 2
• %c: the character represented by the corresponding Unicode code point
• %d: base 10
• %o: base 8
• %O: base 8 with 0o prefix
• %q: a single-quoted character literal safely escaped with Go syntax
• %x: base 16, with lower-case letters for a-f
• %X: base 16, with upper-case letters for A-F
• %U: Unicode format: U+1234; same as U+%04X

See: pkg.go.dev/fmt