[Go] Package fmt

Package fmt implements formatted I/O with functions analogous to C's printf and scanf.

Description

General

• %v : the value in a default format (when printing structs, adds the plus symbol to field names <%+v>)
• %#v : a Go-syntax representation of the value
• %T : a Go-syntax representation of the type of value

Integer

• %b : base 2
• %d : base 10
• %x : base 16, with lower-case letters for a-f
• %X : base 16, with upper-case letters for A-F

Floating-Point and Complex Constituents

• %f : decimal point but no exponent
  • %w.pf : where w is width and p is precision

String and Slice of Bytes

• %s : the uninterpreted bytes of the string or slice
• %q : a double-quoted string safely escaped with Go syntax

Pointer

• %p : base 16 notation, with leading 0x

Methods

Errorf

Errorf formats according to a format specifier and returns the string as a value that satisfies error.

func Errorf(format string, a ...interface{}) error

Print

Print formats using the default formats for its operands and writes to standard output.

Spaces are added between operands when neither is a string.

It returns the number of bytes written and any write error encountered.

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

Printf

Printf formats according to a format specifier and writes to standard output.

It returns the of bytes written and any write error encountered.

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

Println

Println formats using the default formats for its operands and writes to standard output.

Spaces are always added between operands and a new line is appended.

It returns the number of bytes written and any write error encountered.

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

Sprintf

Sprintf formats according to a format specifier and returns the resulting string.

func Sprintf(format string, a ...interface{}) string

Scan

Scan scans text read from standard input, storing successive space-separated values into successive arguments.

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

Scanf

Scanf scans text read from standard input, storing successive space-separated values into successive arguments as determined by the format.

func Scanf(format string, a ...interface{}) (n int, err error)

Scanln

Scanln is similar to Scan, but stops scanning at a newline and after the final item there must be a newline or EOF.

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

Usage

package main

import "fmt"

func main() {
  fmt.Printf("%7.2f\n", 3.141592)
  str := fmt.Sprintf("%0.3f", 2.71828)
  fmt.Print("Test: ")
  fmt.Println(str)

  // Width, Padding, Alignment
  fmt.Printf("%05d\n", 18)
  fmt.Printf("%-05d\n", 18)
  
  // Scan
  stdin := bufio.NewReader(os.Stdin)
  var a int
  var b int

  n, err := fmt.Scanln(&a, &b)
  if err != nil {
    fmt.Printf("%v\n", err)
    stdin.ReadString('\n')
  } else {
    fmt.Printf("%v, %v, %#v\n", n, a, b)
  }
}
//    3.14
// Test: 2.718
// 00018
// 18