正则表达式匹配对我来说有些奇怪。

huangapple
go评论115阅读模式
英文:

Regex match does weird things for me

问题

我正在尝试创建一个简单的命令行日期输入函数。

在使用golang的正则表达式模式匹配时，我遇到了奇怪的行为：正确的模式匹配返回false，但会干扰我的循环，而不正确的模式只返回false。以下是产生错误的函数：

  1. func ReadDate(fieldname string) (value string) {
  2.     var validID = regexp.MustCompile(`^\d\d\d\d\s(Jan|Feb|Mar|Apr|May|Jun|Jul|Aug|Sep|Oct|Nov|Dez)\s\d\d$`)
  3.     for {
  4.         value = ""
  5.         fmt.Printf("%s - e.g. 2014 Jan 01: ", fieldname)
  6.         fmt.Scanf("%s\n", &value)
  7.         if value == "" {
  8.             break // empty value is ok for input
  9.         }
  10.         fmt.Printf("validid %v\n", validID.MatchString(value))
  11.         if validID.MatchString(value) {
  12.             break
  13.         } else {
  14.             fmt.Printf("invalid entry, try again..\n")
  15.         }
  16.     }
  17.     return
  18. }

当我运行它时，我得到以下结果：

  1. date - e.g. 2014 Jan 01: x
  2. validid false
  3. date - e.g. 2014 Jan 01: x
  4. validid false
  5. date - e.g. 2014 Jan 01: 2014 Jan 01
  6. validid false
  7. date - e.g. 2014 Jan 01: validid false
  8. date - e.g. 2014 Jan 01: validid false
  9. date - e.g. 2014 Jan 01:

请注意，最后一个符合正确模式的输入会再次通过无限循环运行两次，然后停止。有任何想法为什么会发生这种情况吗？

Go版本为1.2，Linux/386。

英文:

I'm trying to create a simple command line date entry function.

I get a weird behavior when using regexp pattern matching with golang: correct pattern mach returns false but messes with my loop while incorrect pattern just returns false. Here is the function that produces the error:

  1. func ReadDate(fieldname string) (value string) {
  2. 	var validID = regexp.MustCompile(`^\d\d\d\d\s(Jan|Feb|Mar|Apr|May|Jun|Jul|Aug|Sep|Oct|Nov|Dez)\s\d\d$`)
  3. 	for {
  4. 		value = ""
  5. 		fmt.Printf("%s - e.g. 2014 Jan 01: ", fieldname)
  6. 		fmt.Scanf("%s\n", &value)
  7. 		if value == "" {
  8. 			break // empty value is ok for input
  9. 		}
  10. 		fmt.Printf("validid %v\n", validID.MatchString(value))
  11. 		if validID.MatchString(value) {
  12. 			break
  13. 		} else {
  14. 			fmt.Printf("invalid entry, try again..\n")
  15. 		}
  16. 	}
  17. 	return
  18. }

when I run it, I get the following:

  1. date - e.g. 2014 Jan 01: x
  2. validid false
  3. date - e.g. 2014 Jan 01: x
  4. validid false
  5. date - e.g. 2014 Jan 01: 2014 Jan 01
  6. validid false
  7. date - e.g. 2014 Jan 01: validid false
  8. date - e.g. 2014 Jan 01: validid false
  9. date - e.g. 2014 Jan 01:

Notice how the last entry with the correct pattern runs another two times through the infinite loop and then stops. Any ideas why this might happen?

Go version 1.2 Linux/386

答案1

得分: 4

问题是Scanf在整行读取之前就返回了。我已经修改了你的代码，使用了bufio.Scanner和os.Stdin，现在它可以正常工作了：

  1. package main
  3. import (
  4. 	"bufio"
  5. 	"fmt"
  6. 	"os"
  7. 	"regexp"
  8. )
  10. func ReadDate(fieldname string) (value string) {
  11. 	var validID = regexp.MustCompile(`^\d\d\d\d\s(Jan|Feb|Mar|Apr|May|Jun|Jul|Aug|Sep|Oct|Nov|Dez)\s\d\d$`)
  12. 	fmt.Printf("%s - 例如 2014 Jan 01: ", fieldname)
  14. 	scanner := bufio.NewScanner(os.Stdin)
  15. 	for scanner.Scan() {
  16. 		value = scanner.Text()
  17. 		fmt.Printf("读取的值: '%s'\n", value)
  18. 		if value == "" {
  19. 			break // 空值对输入来说是可以的
  20. 		}
  21. 		fmt.Printf("validid %v\n", validID.MatchString(value))
  22. 		if validID.MatchString(value) {
  23. 			break
  24. 		} else {
  25. 			fmt.Printf("无效的输入，请重试..\n")
  26. 		}
  27. 		fmt.Printf("%s - 例如 2014 Jan 01: ", fieldname)
  29. 	}
  30. 	return
  31. }
  33. func main() {
  34. 	fmt.Println("返回值: ", ReadDate("foo"))
  35. }
英文:

the problem is Scanf returns before the whole line is read. I've modified your code to use bufio.Scanner and os.Stdin, and it works now:

  1. package main
  3. import (
  4. 	"bufio"
  5. 	"fmt"
  6. 	"os"
  7. 	"regexp"
  8. )
  10. func ReadDate(fieldname string) (value string) {
  11. 	var validID = regexp.MustCompile(`^\d\d\d\d\s(Jan|Feb|Mar|Apr|May|Jun|Jul|Aug|Sep|Oct|Nov|Dez)\s\d\d$`)
  12. 	fmt.Printf("%s - e.g. 2014 Jan 01: ", fieldname)
  14. 	scanner := bufio.NewScanner(os.Stdin)
  15. 	for scanner.Scan() {
  16. 		value = scanner.Text()
  17. 		fmt.Printf("Read value: '%s'\n", value)
  18. 		if value == "" {
  19. 			break // empty value is ok for input
  20. 		}
  21. 		fmt.Printf("validid %v\n", validID.MatchString(value))
  22. 		if validID.MatchString(value) {
  23. 			break
  24. 		} else {
  25. 			fmt.Printf("invalid entry, try again..\n")
  26. 		}
  27. 		fmt.Printf("%s - e.g. 2014 Jan 01: ", fieldname)
  29. 	}
  30. 	return
  31. }
  33. func main() {
  34. 	fmt.Println("Returned ", ReadDate("foo"))
  35. }

huangapple
  • 本文由 发表于 2014年2月17日 20:47:15
  • 转载请务必保留本文链接：https://go.coder-hub.com/21829546.html
  • go
  • regex
匿名

发表评论

匿名网友

:?: :razz: :sad: :evil: :!: :smile: :oops: :grin: :eek: :shock: :???: :cool: :lol: :mad: :twisted: :roll: :wink: :idea: :arrow: :neutral: :cry: :mrgreen:

确定