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 // Return the most recent call to Scan as a []byte.
  35 func 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.
  49 func 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.
  69 func 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.
  99 func 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 }