diff --git a/src/pkg/bufio/bufio.go b/src/pkg/bufio/bufio.go index 33779014c9..ee69c2d31e 100644 --- a/src/pkg/bufio/bufio.go +++ b/src/pkg/bufio/bufio.go @@ -278,7 +278,7 @@ func (b *Reader) ReadSlice(delim byte) (line []byte, err error) { } // 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 @@ func (b *Reader) ReadLine() (line []byte, isPrefix bool, err error) { // 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 @@ func (b *Reader) ReadBytes(delim byte) (line []byte, err error) { // 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 0000000000..b545ce39ae --- /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 +}