在Go语言中，for循环之外的未使用变量。

huangapple
go评论118阅读模式
英文:

Unused variable outside of a for-loop in Go

问题

我无法编译以下Go代码。我一直收到一个错误，说变量'header'未被使用。我正在尝试读取和处理一个CSV文件。文件逐行读取，所以我需要将标题保存到一个“循环外”的变量中，以便在处理CSV行时可以引用它。有人知道我作为一个新的Go用户做错了什么吗？

  1. func main() {
  2.     ...
  3.     inputData := csv.NewReader(file)
  4.     var header []string
  5.     //keep reading the file until EOF is reached
  6.     for j := 0; ; j++ {
  7.         i, err := inputData.Read()
  8.         if err == io.EOF {
  9.             break
  10.         }
  11.         if j == 0 {
  12.             header = i
  13.         } else {
  14.             // Business logic in here
  15.             fmt.Println(i)
  16.             //TODO convert to JSON
  17.             //TODO send to SQS
  18.         }
  19.     }
  20. }

以下是翻译好的代码：

  1. func main() {
  2.     ...
  3.     inputData := csv.NewReader(file)
  4.     var header []string
  5.     // 读取文件直到达到EOF
  6.     for j := 0; ; j++ {
  7.         i, err := inputData.Read()
  8.         if err == io.EOF {
  9.             break
  10.         }
  11.         if j == 0 {
  12.             header = i
  13.         } else {
  14.             // 在这里处理业务逻辑
  15.             fmt.Println(i)
  16.             //TODO 转换为JSON
  17.             //TODO 发送到SQS
  18.         }
  19.     }
  20. }
英文:

I can't compile the following Go code. I keep getting an error that variable 'header' is not used. I'm trying to read and process a CSV file. The file is read line by line an so I need to save the header into a "outside-the-loop" variable I can refer to when processing CSV lines. Anyone knows what I'm doing incorrectly as a new Go user?

  1. func main() {
  2.     ...
  3.     inputData := csv.NewReader(file)
  4.     var header []string
  5.     //keep reading the file until EOF is reached
  6.     for j := 0; ; j++ {
  7. 	    i, err := inputData.Read()
  8. 	    if err == io.EOF {
  9. 		    break
  10. 	    }
  11. 	    if j == 0 {
  12. 		    header = i
  13. 	    } else {
  14. 		    // Business logic in here
  15. 		    fmt.Println(i)
  16. 		    //TODO convert to JSON
  17. 		    //TODO send to SQS
  18. 	    }
  19.     }
  20. }

答案1

得分: 2

你可以将一个空标识符赋值给变量，只是为了能够编译你的代码，例如：_ = header。以下是一个示例：

  1. package main
  3. import (
  4. 	"encoding/csv"
  5. 	"fmt"
  6. 	"io"
  7. 	"strings"
  8. )
  10. func main() {
  12. 	in := `first_name,last_name,username
  13. "Rob","Pike",rob
  14. Ken,Thompson,ken
  15. "Robert","Griesemer","gri"
  16. `
  17. 	file := strings.NewReader(in)
  18. 	inputData := csv.NewReader(file)
  19. 	var header []string
  20. 	//keep reading the file until EOF is reached
  21. 	for j := 0; ; j++ {
  22. 		i, err := inputData.Read()
  23. 		if err == io.EOF {
  24. 			break
  25. 		}
  26. 		if j == 0 {
  27. 			header = i
  28. 		} else {
  29. 			// Business logic in here
  30. 			fmt.Println(i)
  31. 			//TODO convert to JSON
  32. 			//TODO send to SQS
  33. 		}
  34. 	}
  36. 	_ = header
  37. }

你可以在这里运行这段代码：https://go.dev/play/p/BrmYU2zAc9f

英文:

You can assign to a blank identifier just to be able to compile your code, like: _ = header. As example:

  1. package main
  3. import (
  4. 	"encoding/csv"
  5. 	"fmt"
  6. 	"io"
  7. 	"strings"
  8. )
  10. func main() {
  12. 	in := `first_name,last_name,username
  13. "Rob","Pike",rob
  14. Ken,Thompson,ken
  15. "Robert","Griesemer","gri"
  16. `
  17. 	file := strings.NewReader(in)
  18. 	inputData := csv.NewReader(file)
  19. 	var header []string
  20. 	//keep reading the file until EOF is reached
  21. 	for j := 0; ; j++ {
  22. 		i, err := inputData.Read()
  23. 		if err == io.EOF {
  24. 			break
  25. 		}
  26. 		if j == 0 {
  27. 			header = i
  28. 		} else {
  29. 			// Business logic in here
  30. 			fmt.Println(i)
  31. 			//TODO convert to JSON
  32. 			//TODO send to SQS
  33. 		}
  34. 	}
  36. 	_ = header
  37. }

https://go.dev/play/p/BrmYU2zAc9f

huangapple
  • 本文由 发表于 2022年2月23日 04:00:14
  • 转载请务必保留本文链接：https://go.coder-hub.com/71227596.html
  • for-loop
  • go
  • unused-variables
  • variables
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