1// Copyright 2013 The Go Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style
3// license that can be found in the LICENSE file.
4
5package bufio_test
6
7import (
8	"bufio"
9	"fmt"
10	"os"
11	"strconv"
12	"strings"
13)
14
15func ExampleWriter() {
16	w := bufio.NewWriter(os.Stdout)
17	fmt.Fprint(w, "Hello, ")
18	fmt.Fprint(w, "world!")
19	w.Flush() // Don't forget to flush!
20	// Output: Hello, world!
21}
22
23// The simplest use of a Scanner, to read standard input as a set of lines.
24func ExampleScanner_lines() {
25	scanner := bufio.NewScanner(os.Stdin)
26	for scanner.Scan() {
27		fmt.Println(scanner.Text()) // Println will add back the final '\n'
28	}
29	if err := scanner.Err(); err != nil {
30		fmt.Fprintln(os.Stderr, "reading standard input:", err)
31	}
32}
33
34// Return the most recent call to Scan as a []byte.
35func ExampleScanner_Bytes() {
36	scanner := bufio.NewScanner(strings.NewReader("gopher"))
37	for scanner.Scan() {
38		fmt.Println(len(scanner.Bytes()) == 6)
39	}
40	if err := scanner.Err(); err != nil {
41		fmt.Fprintln(os.Stderr, "shouldn't see an error scanning a string")
42	}
43	// Output:
44	// true
45}
46
47// Use a Scanner to implement a simple word-count utility by scanning the
48// input as a sequence of space-delimited tokens.
49func ExampleScanner_words() {
50	// An artificial input source.
51	const input = "Now is the winter of our discontent,\nMade glorious summer by this sun of York.\n"
52	scanner := bufio.NewScanner(strings.NewReader(input))
53	// Set the split function for the scanning operation.
54	scanner.Split(bufio.ScanWords)
55	// Count the words.
56	count := 0
57	for scanner.Scan() {
58		count++
59	}
60	if err := scanner.Err(); err != nil {
61		fmt.Fprintln(os.Stderr, "reading input:", err)
62	}
63	fmt.Printf("%d\n", count)
64	// Output: 15
65}
66
67// Use a Scanner with a custom split function (built by wrapping ScanWords) to validate
68// 32-bit decimal input.
69func ExampleScanner_custom() {
70	// An artificial input source.
71	const input = "1234 5678 1234567901234567890"
72	scanner := bufio.NewScanner(strings.NewReader(input))
73	// Create a custom split function by wrapping the existing ScanWords function.
74	split := func(data []byte, atEOF bool) (advance int, token []byte, err error) {
75		advance, token, err = bufio.ScanWords(data, atEOF)
76		if err == nil && token != nil {
77			_, err = strconv.ParseInt(string(token), 10, 32)
78		}
79		return
80	}
81	// Set the split function for the scanning operation.
82	scanner.Split(split)
83	// Validate the input
84	for scanner.Scan() {
85		fmt.Printf("%s\n", scanner.Text())
86	}
87
88	if err := scanner.Err(); err != nil {
89		fmt.Printf("Invalid input: %s", err)
90	}
91	// Output:
92	// 1234
93	// 5678
94	// Invalid input: strconv.ParseInt: parsing "1234567901234567890": value out of range
95}
96
97// Use a Scanner with a custom split function to parse a comma-separated
98// list with an empty final value.
99func ExampleScanner_emptyFinalToken() {
100	// Comma-separated list; last entry is empty.
101	const input = "1,2,3,4,"
102	scanner := bufio.NewScanner(strings.NewReader(input))
103	// Define a split function that separates on commas.
104	onComma := func(data []byte, atEOF bool) (advance int, token []byte, err error) {
105		for i := 0; i < len(data); i++ {
106			if data[i] == ',' {
107				return i + 1, data[:i], nil
108			}
109		}
110		if !atEOF {
111			return 0, nil, nil
112		}
113		// There is one final token to be delivered, which may be the empty string.
114		// Returning bufio.ErrFinalToken here tells Scan there are no more tokens after this
115		// but does not trigger an error to be returned from Scan itself.
116		return 0, data, bufio.ErrFinalToken
117	}
118	scanner.Split(onComma)
119	// Scan.
120	for scanner.Scan() {
121		fmt.Printf("%q ", scanner.Text())
122	}
123	if err := scanner.Err(); err != nil {
124		fmt.Fprintln(os.Stderr, "reading input:", err)
125	}
126	// Output: "1" "2" "3" "4" ""
127}
128