Go运行时错误：“对nil映射中的条目进行赋值”

huangapple
go评论197阅读模式
英文:

Go Runtime error: “assignment to entry in nil map”

问题

你的代码中出现了一个错误。错误信息是"panic: assignment to entry in nil map"，意味着在nil映射中进行了赋值操作。

具体来说，问题出现在stateInformation结构体的columns字段上。在setColumns方法中，你尝试将值赋给info.columns[column]，但是columns映射是nil的，没有被初始化。

为了解决这个问题，你需要在stateInformation结构体的setColumns方法中初始化columns映射。你可以在setColumns方法的开头添加以下代码：

  1. if info.columns == nil {
  2.     info.columns = make(map[string]int)
  3. }

这样，当columns映射为nil时，它将被初始化为空映射。这样就可以安全地对其进行赋值操作了。

修复后的代码如下所示：

  1. func (info *stateInformation) setColumns(record []string) {
  2.     if info.columns == nil {
  3.         info.columns = make(map[string]int)
  4.     }
  5.     for idx, column := range record {
  6.         info.columns[column] = idx
  7.     }
  8. }

希望这可以帮助到你！如果你还有其他问题，请随时提问。

英文:

I'm new in go lang. I'm trying to read csv file and collecting data.

But after run it I got this error :

  1. panic: assignment to entry in nil map
  3. goroutine 1 [running]:
  4. panic(0x4dedc0, 0xc082002440)
  5.         C:/Go/src/runtime/panic.go:464 +0x3f4
  6. main.(*stateInformation).setColumns(0xc08202bd40, 0xc082060000, 0x11, 0x20)
  7.         F:/Works/Go/src/examples/state-info/main.go:25 +0xda
  8. main.main()
  9.         F:/Works/Go/src/examples/state-info/main.go:69 +0xaea

My code :

  1. package main
  3. import (
  4. 	"encoding/csv"
  5. 	"fmt"
  6. 	"io"
  7. 	"log"
  8. 	"os"
  9. 	"strconv"
  10. )
  12. type stateInformation struct {
  13. 	columns map[string]int
  14. }
  16. type state struct {
  17. 	id               int
  18. 	name             string
  19. 	abbreviation     string
  20. 	censusRegionName string
  21. }
  23. func (info *stateInformation) setColumns(record []string) {
  24. 	for idx, column := range record {
  25. 		info.columns[column] = idx
  26. 	}
  27. }
  29. func (info *stateInformation) parseState(record []string) (*state, error) {
  30. 	column := info.columns["id"]
  31. 	id, err := strconv.Atoi(record[column])
  32. 	if err != nil {
  33. 		return nil, err
  34. 	}
  35. 	name := record[info.columns["name"]]
  36. 	abbreviation := record[info.columns["abbreviation"]]
  37. 	censusRegionName := record[info.columns["census_region_name"]]
  38. 	return &state{
  39. 		id:               id,
  40. 		name:             name,
  41. 		abbreviation:     abbreviation,
  42. 		censusRegionName: censusRegionName,
  43. 	}, nil
  44. }
  46. func main() {
  47. 	// #1 open a file
  48. 	f, err := os.Open("state_table.csv")
  49. 	if err != nil {
  50. 		log.Fatalln(err)
  51. 	}
  52. 	defer f.Close()
  54. 	stateLookup := map[string]*state{}
  56. 	info := &stateInformation{}
  58. 	// #2 parse a csv file
  59. 	csvReader := csv.NewReader(f)
  60. 	for rowCount := 0; ; rowCount++ {
  61. 		record, err := csvReader.Read()
  62. 		if err == io.EOF {
  63. 			break
  64. 		} else if err != nil {
  65. 			log.Fatalln(err)
  66. 		}
  68. 		if rowCount == 0 {
  69. 			info.setColumns(record)
  70. 		} else {
  71. 			state, err := info.parseState(record)
  72. 			if err != nil {
  73. 				log.Fatalln(err)
  74. 			}
  75. 			stateLookup[state.abbreviation] = state
  76. 		}
  77. 	}
  79. 	// state-information AL
  80. 	if len(os.Args) < 2 {
  81. 		log.Fatalln("expected state abbreviation")
  82. 	}
  83. 	abbreviation := os.Args[1]
  84. 	state, ok := stateLookup[abbreviation]
  85. 	if !ok {
  86. 		log.Fatalln("invalid state abbreviation")
  87. 	}
  89. 	fmt.Println(`
  90. <html>
  91.     <head></head>
  92.     <body>
  93.       <table>
  94.         <tr>
  95.           <th>Abbreviation</th>
  96.           <th>Name</th>
  97.         </tr>`)
  99. 	fmt.Println(`
  100.         <tr>
  101.           <td>` + state.abbreviation + `</td>
  102.           <td>` + state.name + `</td>
  103.         </tr>
  104.     `)
  106. 	fmt.Println(`
  107.       </table>
  108.     </body>
  109. </html>
  110.     `)
  111. }

What's wrong in my code?

答案1

得分: 4

我不知道你想要获得什么，但错误提示显示，在赋值时columns映射没有column索引，因此引发了恐慌。

  1. 恐慌：在空映射中赋值

要使其正常工作，你需要在开始填充索引之前初始化映射本身。

  1. state := &stateInformation{
  2.     columns: make(map[string]int),
  3. }

或者另一种初始化方式：

  1. func (info *stateInformation) setColumns(record []string) {
  2.     info.columns = make(map[string]int)
  3.     
  4.     for idx, column := range record {
  5.         info.columns[column] = idx
  6.     }
  7. }
英文:

I don't know what you are trying to obtain, but the error tells, that columns map does not have a column index on the moment of assignment and for this reason is throwing a panic.

  1. panic: assignment to entry in nil map

To make it work you have to initialize the map itself before to start to populate with indexes.

  1. state := &stateInformation{
  2.     columns: make(map[string]int),
  3. }

Or another way to initialize:

  1. func (info *stateInformation) setColumns(record []string) {
  2.     info.columns = make(map[string]int)
  3.     
  4.     for idx, column := range record {
  5.         info.columns[column] = idx
  6.     }
  7. }

huangapple
  • 本文由 发表于 2016年3月14日 19:42:36
  • 转载请务必保留本文链接：https://go.coder-hub.com/35986604.html
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