formatting.go

package main

import (
	"fmt"
	"os"
)

type point struct {
	x, y int
}

// Go offers excellent support for string formatting in the printf tradition.
func main() {
	// Go offers several printing “verbs” designed to format general Go values.

	// For example, this prints an instance of our point struct.
	p := point{1, 2}
	fmt.Printf("%v\n", p)

	// If the value is a struct, the %+v variant will include the struct’s field names.
	fmt.Printf("%+v\n", p)

	// The %#v variant prints a Go syntax representation of the value, i.e. the source
	// code snippet that would produce that value.
	fmt.Printf("%#v\n", p)

	// To print the type of a value, use %T.
	fmt.Printf("%T\n", p)

	// Formatting booleans is straight-forward.
	fmt.Printf("%t\n", true)

	// There are many options for formatting integers.
	// Use %d for standard, base-10 formatting.
	fmt.Printf("%d\n", 123)

	// This prints a binary representation.
	fmt.Printf("%b\n", 14)

	// This prints the character corresponding to the given integer.
	fmt.Printf("%c\n", 33)

	// %x provides hex encoding.
	fmt.Printf("%x\n", 456)

	// There are also several formatting options for floats.
	// For basic decimal formatting use %f.
	fmt.Printf("%f\n", 78.9)

	// %e and %E format the float in (slightly different versions of) scientific
	// notation.
	fmt.Printf("%e\n", 123400000.0)
	fmt.Printf("%E\n", 123400000.0)

	// For basic string printing use %s.
	fmt.Printf("%s\n", "\"string\"")

	// To double-quote strings as in Go source, use %q.
	fmt.Printf("%q\n", "\"string\"")

	// As with integers seen earlier, %x renders the string in base-16, with two
	// output characters per byte of input.
	fmt.Printf("%x\n", "hex this")

	// To print a representation of a pointer, use %p.
	fmt.Printf("%p\n", &p)

	/*
		When formatting numbers you will often want to control the width and precision
		of the resulting figure. To specify the width of an integer, use a number after
		the % in the verb. By default the result will be right-justified and padded
		with spaces.
	*/
	fmt.Printf("|%6d|%6d|\n", 12, 345)

	// You can also specify the width of printed floats, though usually you’ll also want
	// to restrict the decimal precision at the same time with the width.precision syntax.
	fmt.Printf("|%6.2f|%6.2f|\n", 1.2, 3.45)

	// To left-justify, use the - flag.
	fmt.Printf("|%-6.2f|%-6.2f|\n", 1.2, 3.45)

	// You may also want to control width when formatting strings, especially to ensure
	// that they align in table-like output. For basic right-justified width.
	fmt.Printf("|%6s|%6s|\n", "foo", "b")

	// To left-justify use the - flag as with numbers.
	fmt.Printf("|%-6s|%-6s|\n", "foo", "b")

	// So far we’ve seen Printf, which prints the formatted string to os.Stdout.
	// Sprintf formats and returns a string without printing it anywhere.
	s := fmt.Sprintf("a %s", "string")
	fmt.Println(s)

	// You can format+print to io.Writers other than os.Stdout using Fprintf.
	fmt.Fprintf(os.Stderr, "an %s\n", "error")
}