mirror of
https://github.com/golang/go
synced 2024-11-20 03:04:40 -07:00
ec12754700
The Scan function's interface to the split function was not sufficient to handle an empty final token in a pure function; state was required. This was ugly. We introduce a special error value that a split function can return that signals that this token is OK, but is the last one and scanning should stop immediately _after_ this token. The same effect could be achieved using the same trick (a special error value) and checking for that error after Scan finishes, but it's a little clumsy. Providing a published sentinel value in bufio is cleaner and means everyone can use the same trick. The result is an error-free scan. Rewrite the test (that was only barely working) to use the value and be more robust. Also write a new example showing how to do it. Fixes #11836 Change-Id: Iaae77d0f95b4a2efa0175ced94d93c66353079e8 Reviewed-on: https://go-review.googlesource.com/14924 Reviewed-by: Ian Lance Taylor <iant@golang.org>
112 lines
3.3 KiB
Go
112 lines
3.3 KiB
Go
// 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" ""
|
|
}
|