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go/src/time/example_test.go
Rob Pike 8537ccdd7f time: add a thorough example for time.Format
People will still not look at it, but at least we will have a stronger defense.

Change-Id: Ieea6a3d42d06e1067e424e35b87dbcb01c9523cb
Reviewed-on: https://go-review.googlesource.com/7859
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
2015-03-26 18:44:42 +00:00

271 lines
8.4 KiB
Go

// Copyright 2011 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package time_test
import (
"fmt"
"time"
)
func expensiveCall() {}
func ExampleDuration() {
t0 := time.Now()
expensiveCall()
t1 := time.Now()
fmt.Printf("The call took %v to run.\n", t1.Sub(t0))
}
var c chan int
func handle(int) {}
func ExampleAfter() {
select {
case m := <-c:
handle(m)
case <-time.After(5 * time.Minute):
fmt.Println("timed out")
}
}
func ExampleSleep() {
time.Sleep(100 * time.Millisecond)
}
func statusUpdate() string { return "" }
func ExampleTick() {
c := time.Tick(1 * time.Minute)
for now := range c {
fmt.Printf("%v %s\n", now, statusUpdate())
}
}
func ExampleMonth() {
_, month, day := time.Now().Date()
if month == time.November && day == 10 {
fmt.Println("Happy Go day!")
}
}
func ExampleDate() {
t := time.Date(2009, time.November, 10, 23, 0, 0, 0, time.UTC)
fmt.Printf("Go launched at %s\n", t.Local())
// Output: Go launched at 2009-11-10 15:00:00 -0800 PST
}
func ExampleTime_Format() {
// Parse a time value from a string in the standard Unix format.
t, err := time.Parse(time.UnixDate, "Sat Mar 7 11:06:39 PST 2015")
if err != nil { // Always check errors even if they should not happen.
panic(err)
}
// time.Time's Stringer method is useful without any format.
fmt.Println("default format:", t)
// Predefined constants in the package implement common layouts.
fmt.Println("Unix format:", t.Format(time.UnixDate))
// The time zone attached to the time value affects its output.
fmt.Println("Same, in UTC:", t.UTC().Format(time.UnixDate))
// The rest of this function demonstrates the properties of the
// layout string used in the format.
// The layout string used by the Parse function and Format method
// shows by example how the reference time should be represented.
// We stress that one must show how the reference time is formatted,
// not a time of the user's choosing. Thus each layout string is a
// representation of the time stamp,
// Jan 2 15:04:05 2006 MST
// An easy way to remember this value is that it holds, when presented
// in this order, the values (lined up with the elements above):
// 1 2 3 4 5 6 -7
// There are some wrinkles illustrated below.
// Most uses of Format and Parse use constant layout strings such as
// the ones defined in this package, but the interface is flexible,
// as these examples show.
// Define a helper function to make the examples' output look nice.
do := func(name, layout, want string) {
got := t.Format(layout)
if want != got {
fmt.Printf("error: for %q got %q; expected %q\n", layout, got, want)
return
}
fmt.Printf("%-15s %q gives %q\n", name, layout, got)
}
// Print a header in our output.
fmt.Printf("\nFormats:\n\n")
// A simple starter example.
do("Basic", "Mon Jan 2 15:04:05 MST 2006", "Sat Mar 7 11:06:39 PST 2015")
// For fixed-width printing of values, such as the date, that may be one or
// two characters (7 vs. 07), use an _ instead of a space in the layout string.
// Here we print just the day, which is 2 in our layout string and 7 in our
// value.
do("No pad", "<2>", "<7>")
// An underscore represents a zero pad, if required.
do("Spaces", "<_2>", "< 7>")
// Similarly, a 0 indicates zero padding.
do("Zeros", "<02>", "<07>")
// If the value is already the right width, padding is not used.
// For instance, the second (05 in the reference time) in our value is 39,
// so it doesn't need padding, but the minutes (04, 06) does.
do("Suppressed pad", "04:05", "06:39")
// The predefined constant Unix uses an underscore to pad the day.
// Compare with our simple starter example.
do("Unix", time.UnixDate, "Sat Mar 7 11:06:39 PST 2015")
// The hour of the reference time is 15, or 3PM. The layout can express
// it either way, and since our value is the morning we should see it as
// an AM time. We show both in one format string. Lower case too.
do("AM/PM", "3PM==3pm==15h", "11AM==11am==11h")
// When parsing, if the seconds value is followed by a decimal point
// and some digits, that is taken as a fraction of a second even if
// the layout string does not represent the fractional second.
// Here we add a fractional second to our time value used above.
t, err = time.Parse(time.UnixDate, "Sat Mar 7 11:06:39.1234 PST 2015")
if err != nil {
panic(err)
}
// It does not appear in the output if the layout string does not contain
// a representation of the fractional second.
do("No fraction", time.UnixDate, "Sat Mar 7 11:06:39 PST 2015")
// Fractional seconds can be printed by adding a run of 0s or 9s after
// a decimal point in the seconds value in the layout string.
// If the layout digits are 0s, the fractional second is of the specified
// width. Note that the output has a trailing zero.
do("0s for fraction", "15:04:05.00000", "11:06:39.12340")
// If the fraction in the layout is 9s, trailing zeros are dropped.
do("9s for fraction", "15:04:05.99999999", "11:06:39.1234")
// Output:
// default format: 2015-03-07 11:06:39 -0800 PST
// Unix format: Sat Mar 7 11:06:39 PST 2015
// Same, in UTC: Sat Mar 7 19:06:39 UTC 2015
//
// Formats:
//
// Basic "Mon Jan 2 15:04:05 MST 2006" gives "Sat Mar 7 11:06:39 PST 2015"
// No pad "<2>" gives "<7>"
// Spaces "<_2>" gives "< 7>"
// Zeros "<02>" gives "<07>"
// Suppressed pad "04:05" gives "06:39"
// Unix "Mon Jan _2 15:04:05 MST 2006" gives "Sat Mar 7 11:06:39 PST 2015"
// AM/PM "3PM==3pm==15h" gives "11AM==11am==11h"
// No fraction "Mon Jan _2 15:04:05 MST 2006" gives "Sat Mar 7 11:06:39 PST 2015"
// 0s for fraction "15:04:05.00000" gives "11:06:39.12340"
// 9s for fraction "15:04:05.99999999" gives "11:06:39.1234"
}
func ExampleParse() {
// See the example for time.Format for a thorough description of how
// to define the layout string to parse a time.Time value; Parse and
// Format use the same model to describe their input and output.
// longForm shows by example how the reference time would be represented in
// the desired layout.
const longForm = "Jan 2, 2006 at 3:04pm (MST)"
t, _ := time.Parse(longForm, "Feb 3, 2013 at 7:54pm (PST)")
fmt.Println(t)
// shortForm is another way the reference time would be represented
// in the desired layout; it has no time zone present.
// Note: without explicit zone, returns time in UTC.
const shortForm = "2006-Jan-02"
t, _ = time.Parse(shortForm, "2013-Feb-03")
fmt.Println(t)
// Output:
// 2013-02-03 19:54:00 -0800 PST
// 2013-02-03 00:00:00 +0000 UTC
}
func ExampleParseInLocation() {
loc, _ := time.LoadLocation("Europe/Berlin")
const longForm = "Jan 2, 2006 at 3:04pm (MST)"
t, _ := time.ParseInLocation(longForm, "Jul 9, 2012 at 5:02am (CEST)", loc)
fmt.Println(t)
// Note: without explicit zone, returns time in given location.
const shortForm = "2006-Jan-02"
t, _ = time.ParseInLocation(shortForm, "2012-Jul-09", loc)
fmt.Println(t)
// Output:
// 2012-07-09 05:02:00 +0200 CEST
// 2012-07-09 00:00:00 +0200 CEST
}
func ExampleTime_Round() {
t := time.Date(0, 0, 0, 12, 15, 30, 918273645, time.UTC)
round := []time.Duration{
time.Nanosecond,
time.Microsecond,
time.Millisecond,
time.Second,
2 * time.Second,
time.Minute,
10 * time.Minute,
time.Hour,
}
for _, d := range round {
fmt.Printf("t.Round(%6s) = %s\n", d, t.Round(d).Format("15:04:05.999999999"))
}
// Output:
// t.Round( 1ns) = 12:15:30.918273645
// t.Round( 1µs) = 12:15:30.918274
// t.Round( 1ms) = 12:15:30.918
// t.Round( 1s) = 12:15:31
// t.Round( 2s) = 12:15:30
// t.Round( 1m0s) = 12:16:00
// t.Round( 10m0s) = 12:20:00
// t.Round(1h0m0s) = 12:00:00
}
func ExampleTime_Truncate() {
t, _ := time.Parse("2006 Jan 02 15:04:05", "2012 Dec 07 12:15:30.918273645")
trunc := []time.Duration{
time.Nanosecond,
time.Microsecond,
time.Millisecond,
time.Second,
2 * time.Second,
time.Minute,
10 * time.Minute,
time.Hour,
}
for _, d := range trunc {
fmt.Printf("t.Truncate(%6s) = %s\n", d, t.Truncate(d).Format("15:04:05.999999999"))
}
// Output:
// t.Truncate( 1ns) = 12:15:30.918273645
// t.Truncate( 1µs) = 12:15:30.918273
// t.Truncate( 1ms) = 12:15:30.918
// t.Truncate( 1s) = 12:15:30
// t.Truncate( 2s) = 12:15:30
// t.Truncate( 1m0s) = 12:15:00
// t.Truncate( 10m0s) = 12:10:00
// t.Truncate(1h0m0s) = 12:00:00
}