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Source file src/bufio/example_test.go

Documentation: bufio

  // Copyright 2013 The Go Authors. All rights reserved.
  // Use of this source code is governed by a BSD-style
  // license that can be found in the LICENSE file.
  
  package bufio_test
  
  import (
  	"bufio"
  	"fmt"
  	"os"
  	"strconv"
  	"strings"
  )
  
  func ExampleWriter() {
  	w := bufio.NewWriter(os.Stdout)
  	fmt.Fprint(w, "Hello, ")
  	fmt.Fprint(w, "world!")
  	w.Flush() // Don't forget to flush!
  	// Output: Hello, world!
  }
  
  // The simplest use of a Scanner, to read standard input as a set of lines.
  func ExampleScanner_lines() {
  	scanner := bufio.NewScanner(os.Stdin)
  	for scanner.Scan() {
  		fmt.Println(scanner.Text()) // Println will add back the final '\n'
  	}
  	if err := scanner.Err(); err != nil {
  		fmt.Fprintln(os.Stderr, "reading standard input:", err)
  	}
  }
  
  // Use a Scanner to implement a simple word-count utility by scanning the
  // input as a sequence of space-delimited tokens.
  func ExampleScanner_words() {
  	// An artificial input source.
  	const input = "Now is the winter of our discontent,\nMade glorious summer by this sun of York.\n"
  	scanner := bufio.NewScanner(strings.NewReader(input))
  	// Set the split function for the scanning operation.
  	scanner.Split(bufio.ScanWords)
  	// Count the words.
  	count := 0
  	for scanner.Scan() {
  		count++
  	}
  	if err := scanner.Err(); err != nil {
  		fmt.Fprintln(os.Stderr, "reading input:", err)
  	}
  	fmt.Printf("%d\n", count)
  	// Output: 15
  }
  
  // Use a Scanner with a custom split function (built by wrapping ScanWords) to validate
  // 32-bit decimal input.
  func ExampleScanner_custom() {
  	// An artificial input source.
  	const input = "1234 5678 1234567901234567890"
  	scanner := bufio.NewScanner(strings.NewReader(input))
  	// Create a custom split function by wrapping the existing ScanWords function.
  	split := func(data []byte, atEOF bool) (advance int, token []byte, err error) {
  		advance, token, err = bufio.ScanWords(data, atEOF)
  		if err == nil && token != nil {
  			_, err = strconv.ParseInt(string(token), 10, 32)
  		}
  		return
  	}
  	// Set the split function for the scanning operation.
  	scanner.Split(split)
  	// Validate the input
  	for scanner.Scan() {
  		fmt.Printf("%s\n", scanner.Text())
  	}
  
  	if err := scanner.Err(); err != nil {
  		fmt.Printf("Invalid input: %s", err)
  	}
  	// Output:
  	// 1234
  	// 5678
  	// Invalid input: strconv.ParseInt: parsing "1234567901234567890": value out of range
  }
  
  // Use a Scanner with a custom split function to parse a comma-separated
  // list with an empty final value.
  func ExampleScanner_emptyFinalToken() {
  	// Comma-separated list; last entry is empty.
  	const input = "1,2,3,4,"
  	scanner := bufio.NewScanner(strings.NewReader(input))
  	// Define a split function that separates on commas.
  	onComma := func(data []byte, atEOF bool) (advance int, token []byte, err error) {
  		for i := 0; i < len(data); i++ {
  			if data[i] == ',' {
  				return i + 1, data[:i], nil
  			}
  		}
  		// There is one final token to be delivered, which may be the empty string.
  		// Returning bufio.ErrFinalToken here tells Scan there are no more tokens after this
  		// but does not trigger an error to be returned from Scan itself.
  		return 0, data, bufio.ErrFinalToken
  	}
  	scanner.Split(onComma)
  	// Scan.
  	for scanner.Scan() {
  		fmt.Printf("%q ", scanner.Text())
  	}
  	if err := scanner.Err(); err != nil {
  		fmt.Fprintln(os.Stderr, "reading input:", err)
  	}
  	// Output: "1" "2" "3" "4" ""
  }
  

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