example_test.go

Documentation: bufio

     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  }
   128
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