String Formatting

• General:

  Placeholder	Description	Usage	Output
  %v	Default variable format.	("%v", 123)	123
  %+v	Struct format with field names.	("%+v", Person{Name: "John", Age: 35})	{Name:John Age:35}
  %#v	Go syntax representation of the value.	("%#v", []int{1, 2, 3})	[]int{1, 2, 3}
  %T	Type of the value.	("%T", 123)	int
  %p	Hexadecimal memory address.	("%p", &x)	0xc000098040
  %%	Literal % sign.	("%%")	%

• Boolean:

  Placeholder	Description	Usage	Output
  %t	Boolean value.	("%t", true)	true

• Integer:

  Placeholder	Description	Usage	Output
  %d	Integer in base 10.	("%d", 123), ("%d", 'A')	123, 65
  %b	Integer in base 2.	("%b", 123)	1111011
  %o	Integer in base 8.	("%o", 123)	173
  %x	Integer in base 16 with lowercase letters.	("%x", 123)	7b
  %X	Integer in base 16 with uppercase letters.	("%X", 123) , ("%X", 'é')	7B, E9
  %c	Unicode code point character.	("%c", 65), ("%c", 'A')	A, A
  %U	Unicode code point.	("%U", 65), ("%U", 'é')	U+0041, U+00E9

• Floats:

  Placeholder	Description	Usage	Output
  %f	Decimal format for floating-point numbers.	("%f", 123.456)	123.456000
  %e	Scientific notation with lowercase e.	("%e", 123.456)	1.234560e+02
  %E	Scientific notation with uppercase E.	("%E", 123.456)	1.234560E+02

• String (slice of bytes):

  Placeholder	Description	Usage	Output
  %s	String (uninterpreted) without quotes.	("%s", "hello \n")	hello \n
  %q	Double-quoted string.	("%q", "hello")	"hello"

Examples:

1. name := "John"
   age := 35
   char := 97
   fmt.Printf("Name: %s, Age: %d, Char: %c ", name, age, char) // Name: John, Age: 35, Char: a

2. pi := 3.14159
   fmt.Printf("Pi: %.2f", pi) // Pi: 3.14

3. You can also use [n] to explicitly reference the nth argument in fmt, which lets you reuse (optimize) the same already-evaluated value multiple times.

   func expensiveFunc(a int) int {
   	fmt.Println("Calculated")
   	return a
   }

   • Unoptimized:

     func main() {
     	fmt.Printf("%v and %v", expensiveFunc(5), expensiveFunc(5))
     }
     
     // Calculated
     // Calculated
     // 5 and 5

   • Optimized:

     func main() {
     	fmt.Printf("%[1]v and %[1]v", expensiveFunc(5))
     }
     
     // Calculated
     // 5 and 5