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 func ExampleWriter_AvailableBuffer() {
  24         w := bufio.NewWriter(os.Stdout)
  25         for _, i := range []int64{1, 2, 3, 4} {
  26                 b := w.AvailableBuffer()
  27                 b = strconv.AppendInt(b, i, 10)
  28                 b = append(b, ' ')
  29                 w.Write(b)
  30         }
  31         w.Flush()
  32         // Output: 1 2 3 4
  33 }
  34
  35 // The simplest use of a Scanner, to read standard input as a set of lines.
  36 func ExampleScanner_lines() {
  37         scanner := bufio.NewScanner(os.Stdin)
  38         for scanner.Scan() {
  39                 fmt.Println(scanner.Text()) // Println will add back the final '\n'
  40         }
  41         if err := scanner.Err(); err != nil {
  42                 fmt.Fprintln(os.Stderr, "reading standard input:", err)
  43         }
  44 }
  45
  46 // Return the most recent call to Scan as a []byte.
  47 func ExampleScanner_Bytes() {
  48         scanner := bufio.NewScanner(strings.NewReader("gopher"))
  49         for scanner.Scan() {
  50                 fmt.Println(len(scanner.Bytes()) == 6)
  51         }
  52         if err := scanner.Err(); err != nil {
  53                 fmt.Fprintln(os.Stderr, "shouldn't see an error scanning a string")
  54         }
  55         // Output:
  56         // true
  57 }
  58
  59 // Use a Scanner to implement a simple word-count utility by scanning the
  60 // input as a sequence of space-delimited tokens.
  61 func ExampleScanner_words() {
  62         // An artificial input source.
  63         const input = "Now is the winter of our discontent,\nMade glorious summer by this sun of York.\n"
  64         scanner := bufio.NewScanner(strings.NewReader(input))
  65         // Set the split function for the scanning operation.
  66         scanner.Split(bufio.ScanWords)
  67         // Count the words.
  68         count := 0
  69         for scanner.Scan() {
  70                 count++
  71         }
  72         if err := scanner.Err(); err != nil {
  73                 fmt.Fprintln(os.Stderr, "reading input:", err)
  74         }
  75         fmt.Printf("%d\n", count)
  76         // Output: 15
  77 }
  78
  79 // Use a Scanner with a custom split function (built by wrapping ScanWords) to validate
  80 // 32-bit decimal input.
  81 func ExampleScanner_custom() {
  82         // An artificial input source.
  83         const input = "1234 5678 1234567901234567890"
  84         scanner := bufio.NewScanner(strings.NewReader(input))
  85         // Create a custom split function by wrapping the existing ScanWords function.
  86         split := func(data []byte, atEOF bool) (advance int, token []byte, err error) {
  87                 advance, token, err = bufio.ScanWords(data, atEOF)
  88                 if err == nil && token != nil {
  89                         _, err = strconv.ParseInt(string(token), 10, 32)
  90                 }
  91                 return
  92         }
  93         // Set the split function for the scanning operation.
  94         scanner.Split(split)
  95         // Validate the input
  96         for scanner.Scan() {
  97                 fmt.Printf("%s\n", scanner.Text())
  98         }
  99
 100         if err := scanner.Err(); err != nil {
 101                 fmt.Printf("Invalid input: %s", err)
 102         }
 103         // Output:
 104         // 1234
 105         // 5678
 106         // Invalid input: strconv.ParseInt: parsing "1234567901234567890": value out of range
 107 }
 108
 109 // Use a Scanner with a custom split function to parse a comma-separated
 110 // list with an empty final value.
 111 func ExampleScanner_emptyFinalToken() {
 112         // Comma-separated list; last entry is empty.
 113         const input = "1,2,3,4,"
 114         scanner := bufio.NewScanner(strings.NewReader(input))
 115         // Define a split function that separates on commas.
 116         onComma := func(data []byte, atEOF bool) (advance int, token []byte, err error) {
 117                 for i := 0; i < len(data); i++ {
 118                         if data[i] == ',' {
 119                                 return i + 1, data[:i], nil
 120                         }
 121                 }
 122                 if !atEOF {
 123                         return 0, nil, nil
 124                 }
 125                 // There is one final token to be delivered, which may be the empty string.
 126                 // Returning bufio.ErrFinalToken here tells Scan there are no more tokens after this
 127                 // but does not trigger an error to be returned from Scan itself.
 128                 return 0, data, bufio.ErrFinalToken
 129         }
 130         scanner.Split(onComma)
 131         // Scan.
 132         for scanner.Scan() {
 133                 fmt.Printf("%q ", scanner.Text())
 134         }
 135         if err := scanner.Err(); err != nil {
 136                 fmt.Fprintln(os.Stderr, "reading input:", err)
 137         }
 138         // Output: "1" "2" "3" "4" ""
 139 }