bufio: add examples for Scanner
Mention Scanner in docs for ReadLine etc.
R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/7375045
diff --git a/src/pkg/bufio/bufio.go b/src/pkg/bufio/bufio.go
index 3377901..ee69c2d 100644
--- a/src/pkg/bufio/bufio.go
+++ b/src/pkg/bufio/bufio.go
@@ -278,7 +278,7 @@
}
// ReadLine is a low-level line-reading primitive. Most callers should use
-// ReadBytes('\n') or ReadString('\n') instead.
+// ReadBytes('\n') or ReadString('\n') instead or use a Scanner.
//
// ReadLine tries to return a single line, not including the end-of-line bytes.
// If the line was too long for the buffer then isPrefix is set and the
@@ -331,6 +331,7 @@
// it returns the data read before the error and the error itself (often io.EOF).
// ReadBytes returns err != nil if and only if the returned data does not end in
// delim.
+// For simple uses, a Scanner may be more convenient.
func (b *Reader) ReadBytes(delim byte) (line []byte, err error) {
// Use ReadSlice to look for array,
// accumulating full buffers.
@@ -378,6 +379,7 @@
// it returns the data read before the error and the error itself (often io.EOF).
// ReadString returns err != nil if and only if the returned data does not end in
// delim.
+// For simple uses, a Scanner may be more convenient.
func (b *Reader) ReadString(delim byte) (line string, err error) {
bytes, err := b.ReadBytes(delim)
return string(bytes), err
diff --git a/src/pkg/bufio/example_test.go b/src/pkg/bufio/example_test.go
new file mode 100644
index 0000000..b545ce3
--- /dev/null
+++ b/src/pkg/bufio/example_test.go
@@ -0,0 +1,74 @@
+// 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"
+)
+
+// 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.Stdout, "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.Stdout, "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
+}
