Golang Basic 3 - Basic I/O functions

About fmt package

• Package fmt implements formatted I/O with functions analogous to C's printf and scanf. The format 'verbs' are derived from C's but are simpler.

Import package

import "fmt"

Functions in fmt

• You can get more information from https://golang.org/pkg/fmt/#pkg-index.
  golang
func Errorf(format string, a ...interface{}) error
func Fprint(w io.Writer, a ...interface{}) (n int, err error)
func Fprintf(w io.Writer, format string, a ...interface{}) (n int, err error)
func Fprintln(w io.Writer, a ...interface{}) (n int, err error)
func Fscan(r io.Reader, a ...interface{}) (n int, err error)
func Fscanf(r io.Reader, format string, a ...interface{}) (n int, err error)
func Fscanln(r io.Reader, a ...interface{}) (n int, err error)
func Print(a ...interface{}) (n int, err error)
func Printf(format string, a ...interface{}) (n int, err error)
func Println(a ...interface{}) (n int, err error)
func Scan(a ...interface{}) (n int, err error)
func Scanf(format string, a ...interface{}) (n int, err error)
func Scanln(a ...interface{}) (n int, err error)
func Sprint(a ...interface{}) string
func Sprintf(format string, a ...interface{}) string
func Sprintln(a ...interface{}) string
func Sscan(str string, a ...interface{}) (n int, err error)
func Sscanf(str string, format string, a ...interface{}) (n int, err error)
func Sscanln(str string, a ...interface{}) (n int, err error)


Format string

General

Format	Sense
%v	The value in a default format when printing structs, the plus flag (% v) 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

Format	Sense
%t	The word true or false.

Integer

Format	Sense
%b	base 2
%c	the character represented by the corresponding Unicode code point
%d	base 10
%o	base 8
%O	base 8 with 0o prefi
%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"

Floating-point and complex constituents

Format	Sense
%b	decimalless scientific notation with exponent a power of two, in the manner of strconv.FormatFloat with the 'b' format
%e	scientific notation
%E	scientific notation
%f	decimal point but no exponent
%F	synonym for %f
%g	%e for large exponents, %f otherwise
%G	%E for large exponents, %F otherwise
%x	hexadecimal notation (with decimal power of two exponent)
%X	upper-case hexadecimal notation

String and slice of bytes

Format	Sense
%s	the uninterpreted bytes of the string or slice
%q	a double-quoted string safely escaped with Go syntax
%x	base 16, lower-case, two characters per byte
%X	base 16, upper-case, two characters per byte

Slice

Format	Sense
%p	address of 0th element in base 16 notation, with leading 0x

Pointer

|Format|Sense|
|:-:|:-:|
|%p|base 16 notation, with leading 0x|
- The %b, %d, %o, %x and %X verbs also work with pointers, formatting the value exactly as if it were an integer.

Basic input function

Some functions could get input from console.

func Scan(a ...interface{}) (n int, err error)
func Scanln(a ...interface{}) (n int, err error)

• If you need set string format, you can use Scanf().
• Scanln() will add a end of line symbol at the end of the line.

Basic output function

Some functions could print on the console.

func Print(a ...interface{}) (n int, err error)
func Printf(format string, a ...interface{}) (n int, err error)
func Println(a ...interface{}) (n int, err error)

• If you need set string format, you can use Printf().
• Println() will add a end of line symbol at the end of the line.

Sample

usr@host:go/ # cat l3s1.go
package main
import (
    "fmt"
)
func main(){
    var var1 int
    var var2 int
    fmt.Print("Please input two values (split with blank) : ")
    fmt.Scanln(&var1, &var2)
    fmt.Printf("%d   %d = %d\n", var1, var2, var1   var2)
}
usr@host:go/ # go run l3s1.go
Please input two values (split with blank) : 3 6
3   6 = 9