运行时错误：公共指针中存在无效的内存地址或空指针解引用。

huangapple
go评论104阅读模式
英文:

runtime error: invalid memory address or nil pointer dereference in public pointer

问题

我是一个Node.js开发者，通常在我的应用程序中使用一种结构，其中包含一个配置包/对象，其中包含对我经常使用的库和配置选项的引用。通常，这个配置对象也包含我的数据库连接，并且可以通过我的应用程序访问。

我尝试在Go中构建类似的结构，但失败了。

我的计划是构建一个公共变量，它持有对我的配置结构的引用。但是，当我尝试调用Config.Database时，我得到了以下错误：

  1. 2017/02/19 14:05:44 http: panic serving 127.0.0.1:53554: runtime error: invalid memory address or nil pointer dereference
  2.     goroutine 50 [running]:
  3.     net/http.(*conn).serve.func1(0xc42027c000)
  4.         /usr/local/go/src/net/http/server.go:1491 +0x12a
  5.     panic(0x9f45c0, 0xc42000c100)
  6.         /usr/local/go/src/runtime/panic.go:458 +0x243
  7.     main.SignUp(0xc4202780e0)
  8.         /home/attila/dev/gopath/src/github.com/attilasatan/helloiris/handlers.go:31 +0x258
  9.     ...

这是我的配置文件。你可以看到我在这里使用了tideland/golib/redis来进行Redis连接。

configure.go

  1. package main
  3. import (
  4. 	"fmt"
  5. 	"strconv"
  6. 	"time"
  8. 	"github.com/tideland/golib/redis"
  9. )
  11. /*Configuration是应用程序配置的主要类型*/
  12. type Configuration struct {
  13. 	Database *redis.Connection
  14. }
  16. /*Config是应用程序配置的持有者*/
  17. var Config *Configuration
  19. /*Configure处理数据库连接*/
  20. func Configure() (*Configuration, error) {
  22. 	db, err := redis.Open(redis.TcpConnection("127.0.0.1:6379", 30*time.Second))
  24. 	if err != nil {
  25. 		fmt.Printf("Database connection error")
  26. 		return nil, err
  27. 	}
  28. 	conn, err := db.Connection()
  30. 	n, _ := conn.DoInt("INCR", "IDIDID")
  32. 	fmt.Printf(strconv.Itoa(n))
  34. 	if err != nil {
  35. 		fmt.Printf("Database connection error")
  36. 		return nil, err
  37. 	}
  39. 	/*Config是主要的配置对象*/
  41. 	Config := &Configuration{conn}
  43. 	return Config, err
  44. }

这是我使用Config.Database的地方。

handlers.go

  1. func SignUp(ctx *iris.Context) {
  2. 	mail := ctx.FormValue("email")
  3. 	password := ctx.FormValue("password")
  4. 	passwordConfirm := ctx.FormValue("password-confirm")
  6. 	if password != passwordConfirm {
  7. 		ctx.RenderWithStatus(iris.StatusBadRequest, "400.html", ErrorPageData{"passwords dont match"})
  8. 	} else {
  10. 		user := User{mail, password, 0}
  11. 		db := Config.Database
  13. 		userID, err := db.DoInt("INCR", "HELLOIRIS:ID")
  15. 		if err != nil {
  16. 			ctx.RenderWithStatus(iris.StatusBadRequest, "400.html", ErrorPageData{"passwords dont match"})
  17. 		} else {
  19. 			user.ID = userID
  21. 			fmt.Printf("SAVED")
  23. 			ctx.Render("signup-success.html", nil)
  24. 		}
  25. 		ctx.JSON(200, user)
  26. 	}
  27. }

在这次失败之后，我将Configure函数更改如下：

configure.go

  1. func Configure() (Config *Configuration, err error) {
  3. 	if Config != nil {
  4. 		return
  5. 	}
  6. }

并且我在处理程序中更改了使用方式。

handlers.go

  1. config, err := Configure()
  3. if err != nil {
  4. 	ctx.RenderWithStatus(iris.StatusBadRequest, "400.html", ErrorPageData{"try again later"})
  5. 	return
  6. }
  8. user := User{mail, password, 0}
  9. db := config.Database
  11. ... 然后一切都开始完美地工作了。
  13. 我的问题是我根本不明白为什么...为什么我在使用公共指针时会出现恐慌，而在从函数返回相同指针时却没有出现恐慌？
  15. <details>
  16. <summary>英文:</summary>
  18. I&#39;m a nodejs developer and I generally use a structure for my apps which holds a configuration package/object that holds references to my often used libs and configuration options. Generally this configuration object holds my database connections as well and it&#39;s reachable trough my application.
  20. I tried to build similar to this in go and failed horribly. 
  22. My plan was to build a public variable which holds a reference for my config struct. But when I try to call my `Config.Database` I get this panic:
  26.     2017/02/19 14:05:44 http: panic serving 127.0.0.1:53554: runtime error: invalid memory address or nil pointer dereference
  27.         goroutine 50 [running]:
  28.         net/http.(*conn).serve.func1(0xc42027c000)
  29.             /usr/local/go/src/net/http/server.go:1491 +0x12a
  30.         panic(0x9f45c0, 0xc42000c100)
  31.             /usr/local/go/src/runtime/panic.go:458 +0x243
  32.         main.SignUp(0xc4202780e0)
  33.             /home/attila/dev/gopath/src/github.com/attilasatan/helloiris/handlers.go:31 +0x258
  34.         github.com/kataras/iris.HandlerFunc.Serve(0xafaf00, 0xc4202780e0)
  35.             /home/attila/dev/gopath/src/github.com/kataras/iris/http.go:211 +0x30
  36.         github.com/kataras/iris.(*Context).Do(0xc4202780e0)
  37.             /home/attila/dev/gopath/src/github.com/kataras/iris/context.go:152 +0x4d
  38.         github.com/kataras/iris.(*serveMux).BuildHandler.func1(0xc4202780e0)
  39.             /home/attila/dev/gopath/src/github.com/kataras/iris/http.go:1059 +0x6ea
  40.         github.com/kataras/iris.(*Framework).Build.func1.1(0xd87e20, 0xc4202701a0, 0xc420284000)
  41.             /home/attila/dev/gopath/src/github.com/kataras/iris/iris.go:411 +0x72
  42.         net/http.HandlerFunc.ServeHTTP(0xc420235080, 0xd87e20, 0xc4202701a0, 0xc420284000)
  43.             /usr/local/go/src/net/http/server.go:1726 +0x44
  44.         net/http.serverHandler.ServeHTTP(0xc420089f80, 0xd87e20, 0xc4202701a0, 0xc420284000)
  45.             /usr/local/go/src/net/http/server.go:2202 +0x7d
  46.         net/http.(*conn).serve(0xc42027c000, 0xd88820, 0xc42015c200)
  47.             /usr/local/go/src/net/http/server.go:1579 +0x4b7
  48.         created by net/http.(*Server).Serve
  49.             /usr/local/go/src/net/http/server.go:2293 +0x44d
  50.         2017/02/19 14:05:44 http: panic serving 127.0.0.1:53560: runtime error: invalid memory address or nil pointer dereference
  51.         goroutine 51 [running]:
  52.         net/http.(*conn).serve.func1(0xc42027c180)
  53.             /usr/local/go/src/net/http/server.go:1491 +0x12a
  54.         panic(0x9f45c0, 0xc42000c100)
  55.             /usr/local/go/src/runtime/panic.go:458 +0x243
  56.         main.SignUp(0xc4202ac070)
  57.             /home/attila/dev/gopath/src/github.com/attilasatan/helloiris/handlers.go:31 +0x258
  58.         github.com/kataras/iris.HandlerFunc.Serve(0xafaf00, 0xc4202ac070)
  59.             /home/attila/dev/gopath/src/github.com/kataras/iris/http.go:211 +0x30
  60.         github.com/kataras/iris.(*Context).Do(0xc4202ac070)
  61.             /home/attila/dev/gopath/src/github.com/kataras/iris/context.go:152 +0x4d
  62.         github.com/kataras/iris.(*serveMux).BuildHandler.func1(0xc4202ac070)
  63.             /home/attila/dev/gopath/src/github.com/kataras/iris/http.go:1059 +0x6ea
  64.         github.com/kataras/iris.(*Framework).Build.func1.1(0xd87e20, 0xc4202a60d0, 0xc4202840f0)
  65.             /home/attila/dev/gopath/src/github.com/kataras/iris/iris.go:411 +0x72
  66.         net/http.HandlerFunc.ServeHTTP(0xc420235080, 0xd87e20, 0xc4202a60d0, 0xc4202840f0)
  67.             /usr/local/go/src/net/http/server.go:1726 +0x44
  68.         net/http.serverHandler.ServeHTTP(0xc420089f80, 0xd87e20, 0xc4202a60d0, 0xc4202840f0)
  69.             /usr/local/go/src/net/http/server.go:2202 +0x7d
  70.         net/http.(*conn).serve(0xc42027c180, 0xd88820, 0xc42015c480)
  71.             /usr/local/go/src/net/http/server.go:1579 +0x4b7
  72.         created by net/http.(*Server).Serve
  74. Here is my configure file. As you can see I&#39;m using `tideland/golib/redis` for redis connection.
  76. **configure.go**
  78. 	package main
  80. 	import (
  81. 		&quot;fmt&quot;
  82. 		&quot;strconv&quot;
  83. 		&quot;time&quot;
  85. 		&quot;github.com/tideland/golib/redis&quot;
  86. 	)
  88. 	/*Configuration is the main type of app configuration */
  89. 	type Configuration struct {
  90. 		Database *redis.Connection
  91. 	}
  93. 	/*Config is app configuration holder */
  94. 	var Config *Configuration
  96. 	/*Configure handles database connection */
  97. 	func Configure() (*Configuration, error) {
  99. 		db, err := redis.Open(redis.TcpConnection(&quot;127.0.0.1:6379&quot;, 30*time.Second))
  101. 		if err != nil {
  102. 			fmt.Printf(&quot;Database connection error&quot;)
  103. 			return nil, err
  104. 		}
  105. 		conn, err := db.Connection()
  107. 		n, _ := conn.DoInt(&quot;INCR&quot;, &quot;IDIDID&quot;)
  109. 		fmt.Printf(strconv.Itoa(n))
  111. 		if err != nil {
  112. 			fmt.Printf(&quot;Database connection error&quot;)
  113. 			return nil, err
  114. 		}
  116. 		/*Config is the main configuration object*/
  118. 		Config := &amp;Configuration{conn}
  120. 		return Config, err
  121. 	}
  123. And here is where I use `Config.Database`. 
  125. **handlers.go**
  127. 	func SignUp(ctx *iris.Context) {
  128. 		mail := ctx.FormValue(&quot;email&quot;)
  129. 		password := ctx.FormValue(&quot;password&quot;)
  130. 		passwordConfirm := ctx.FormValue(&quot;password-confirm&quot;)
  132. 		if password != passwordConfirm {
  133. 			ctx.RenderWithStatus(iris.StatusBadRequest, &quot;400.html&quot;, ErrorPageData{&quot;passwords dont match&quot;})
  134. 		} else {
  136. 			user := User{mail, password, 0}
  137. 			db := Config.Database
  139. 			userID, err := db.DoInt(&quot;INCR&quot;, &quot;HELLOIRIS:ID&quot;)
  141. 			if err != nil {
  142. 				ctx.RenderWithStatus(iris.StatusBadRequest, &quot;400.html&quot;, ErrorPageData{&quot;passwords dont match&quot;})
  143. 			} else {
  145. 				user.ID = userID
  146. 				
  147. 				fmt.Printf(&quot;SAVED&quot;)
  149. 				ctx.Render(&quot;signup-success.html&quot;, nil)
  150. 			}
  151. 			ctx.JSON(200, user)
  152. 		}
  153. 	}
  155. After this fail I changed `Configure` function like this:
  157. **configure.go**
  159.     func Configure() (Config *Configuration, err error) {
  161.     	if Config != nil {
  162. 		return
  163.     	}
  164.     }
  166. and I changed the usage at handler  
  168. **handlers.go**
  170.     config, err := Configure()
  172. 	if err != nil {
  173. 		ctx.RenderWithStatus(iris.StatusBadRequest, &quot;400.html&quot;, ErrorPageData{&quot;try again later&quot;})
  174. 		return
  175. 	}
  177. 	user := User{mail, password, 0}
  178. 	db := config.Database
  180. ... and everything start to work perfectly.
  182. My problem is I simply don&#39;t understand why... Why did I get this panic when I use a public pointer and why didn&#39;t I get when I returned the same pointer from a function?
  185. </details>
  188. # 答案1
  189. **得分**: 4
  191. 这行代码创建了一个新的本地变量`Config`，所以全局的`Config`变量没有被赋值。去掉冒号，就可以不创建新的变量，而是使用全局的`Config`变量。
  193. <details>
  194. <summary>英文:</summary>
  196.     Config := &amp;Configuration{conn}
  198. This line creates a new __local__ variable `Config` so the global `Config` is never set to anything. Drop the `:` to not create a new variable and use the global `Config` instead.
  200. </details>
  204. # 答案2
  205. **得分**: 1
  207. 你遇到这个问题是因为你的`Config`全局变量没有设置或者仍然保持为nil值。正如错误所说：
  209. &gt; 运行时错误：无效的内存地址或nil指针解引用
  211. 请确保在你的`main`函数中调用`func Configure()`之前调用了处理程序。
  213. 并且根据[tkausl][1]的回答，在你的**configure.go**文件中，将`conn` redis分配给全局变量时删除`:`，使其变为以下形式：
  215.     Config = &amp;Configuration{conn}
  219.   [1]: https://stackoverflow.com/a/42326810/2652524
  221. <details>
  222. <summary>英文:</summary>
  224. You&#39;re getting this problem because your `Config` global variable is not set or still hold nil value. as the error said : 
  226. &gt; runtime error: invalid memory address or nil pointer dereference
  228. Make sure you called 
  229. `func Configure()` before the handler called in your `main` function
  231. and as [tkausl][1] answer remove the `:` when you assign the `conn` redis  to global variable to be like this in your **configure.go** file: 
  233.     Config = &amp;Configuration{conn}
  237.   [1]: https://stackoverflow.com/a/42326810/2652524
  239. </details>

huangapple
  • 本文由 发表于 2017年2月19日 19:37:00
  • 转载请务必保留本文链接：https://go.coder-hub.com/42326753.html
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