io/ioutil: add examples to functions

Change-Id: Ica0cf1ba01ba73bd7e2fe38d653503738a962720
Reviewed-on: https://go-review.googlesource.com/13450Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/io/ioutil/example_test.go

+// Copyright 2015 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 ioutil_test
+
+import (
+	"fmt"
+	"io/ioutil"
+	"log"
+	"os"
+	"path/filepath"
+	"strings"
+)
+
+func ExampleReadAll() {
+	r := strings.NewReader("Go is a general-purpose language designed with systems programming in mind.")
+
+	b, err := ioutil.ReadAll(r)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	fmt.Printf("%s", b)
+
+	// Output:
+	// Go is a general-purpose language designed with systems programming in mind.
+}
+
+func ExampleReadDir() {
+	files, err := ioutil.ReadDir(".")
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	for _, file := range files {
+		fmt.Println(file.Name())
+	}
+}
+
+func ExampleTempDir() {
+	content := []byte("temporary file's content")
+	dir, err := ioutil.TempDir("", "example")
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	defer os.RemoveAll(dir) // clean up
+
+	tmpfn := filepath.Join(dir, "tmpfile")
+	if err := ioutil.WriteFile(tmpfn, content, 0666); err != nil {
+		log.Fatal(err)
+	}
+}
+
+func ExampleTempFile() {
+	content := []byte("temporary file's content")
+	tmpfile, err := ioutil.TempFile("", "example")
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	defer os.Remove(tmpfile.Name()) // clean up
+
+	if _, err := tmpfile.Write(content); err != nil {
+		log.Fatal(err)
+	}
+	if err := tmpfile.Close(); err != nil {
+		log.Fatal(err)
+	}
+}