libgo/go/bufio/example_test.go

   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
   5 package bufio_test
   6
   7 import (
   8         "bufio"
   9         "fmt"
  10         "os"
  11         "strconv"
  12         "strings"
  13 )
  14
  15 func 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.
  24 func 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 // Use a Scanner to implement a simple word-count utility by scanning the
  35 // input as a sequence of space-delimited tokens.
  36 func ExampleScanner_words() {
  37         // An artificial input source.
  38         const input = "Now is the winter of our discontent,\nMade glorious summer by this sun of York.\n"
  39         scanner := bufio.NewScanner(strings.NewReader(input))
  40         // Set the split function for the scanning operation.
  41         scanner.Split(bufio.ScanWords)
  42         // Count the words.
  43         count := 0
  44         for scanner.Scan() {
  45                 count++
  46         }
  47         if err := scanner.Err(); err != nil {
  48                 fmt.Fprintln(os.Stderr, "reading input:", err)
  49         }
  50         fmt.Printf("%d\n", count)
  51         // Output: 15
  52 }
  53
  54 // Use a Scanner with a custom split function (built by wrapping ScanWords) to validate
  55 // 32-bit decimal input.
  56 func ExampleScanner_custom() {
  57         // An artificial input source.
  58         const input = "1234 5678 1234567901234567890"
  59         scanner := bufio.NewScanner(strings.NewReader(input))
  60         // Create a custom split function by wrapping the existing ScanWords function.
  61         split := func(data []byte, atEOF bool) (advance int, token []byte, err error) {
  62                 advance, token, err = bufio.ScanWords(data, atEOF)
  63                 if err == nil && token != nil {
  64                         _, err = strconv.ParseInt(string(token), 10, 32)
  65                 }
  66                 return
  67         }
  68         // Set the split function for the scanning operation.
  69         scanner.Split(split)
  70         // Validate the input
  71         for scanner.Scan() {
  72                 fmt.Printf("%s\n", scanner.Text())
  73         }
  74
  75         if err := scanner.Err(); err != nil {
  76                 fmt.Printf("Invalid input: %s", err)
  77         }
  78         // Output:
  79         // 1234
  80         // 5678
  81         // Invalid input: strconv.ParseInt: parsing "1234567901234567890": value out of range
  82 }
  83
  84 // Use a Scanner with a custom split function to parse a comma-separated
  85 // list with an empty final value.
  86 func ExampleScanner_emptyFinalToken() {
  87         // Comma-separated list; last entry is empty.
  88         const input = "1,2,3,4,"
  89         scanner := bufio.NewScanner(strings.NewReader(input))
  90         // Define a split function that separates on commas.
  91         onComma := func(data []byte, atEOF bool) (advance int, token []byte, err error) {
  92                 for i := 0; i < len(data); i++ {
  93                         if data[i] == ',' {
  94                                 return i + 1, data[:i], nil
  95                         }
  96                 }
  97                 // There is one final token to be delivered, which may be the empty string.
  98                 // Returning bufio.ErrFinalToken here tells Scan there are no more tokens after this
  99                 // but does not trigger an error to be returned from Scan itself.
 100                 return 0, data, bufio.ErrFinalToken
 101         }
 102         scanner.Split(onComma)
 103         // Scan.
 104         for scanner.Scan() {
 105                 fmt.Printf("%q ", scanner.Text())
 106         }
 107         if err := scanner.Err(); err != nil {
 108                 fmt.Fprintln(os.Stderr, "reading input:", err)
 109         }
 110         // Output: "1" "2" "3" "4" ""
 111 }