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82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：

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

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

package main

import (
	"fmt"
	"strconv"
	"time"

	"github.com/tideland/golib/redis"
)

/*Configuration是应用程序配置的主要类型*/
type Configuration struct {
	Database *redis.Connection
}

/*Config是应用程序配置的持有者*/
var Config *Configuration

/*Configure处理数据库连接*/
func Configure() (*Configuration, error) {

	db, err := redis.Open(redis.TcpConnection("127.0.0.1:6379", 30*time.Second))

	if err != nil {
		fmt.Printf("Database connection error")
		return nil, err
	}
	conn, err := db.Connection()

	n, _ := conn.DoInt("INCR", "IDIDID")

	fmt.Printf(strconv.Itoa(n))

	if err != nil {
		fmt.Printf("Database connection error")
		return nil, err
	}

	/*Config是主要的配置对象*/

	Config := &Configuration{conn}

	return Config, err
}

这是我使用Config.Database的地方。

handlers.go

func SignUp(ctx *iris.Context) {
	mail := ctx.FormValue("email")
	password := ctx.FormValue("password")
	passwordConfirm := ctx.FormValue("password-confirm")

	if password != passwordConfirm {
		ctx.RenderWithStatus(iris.StatusBadRequest, "400.html", ErrorPageData{"passwords dont match"})
	} else {

		user := User{mail, password, 0}
		db := Config.Database

		userID, err := db.DoInt("INCR", "HELLOIRIS:ID")

		if err != nil {
			ctx.RenderWithStatus(iris.StatusBadRequest, "400.html", ErrorPageData{"passwords dont match"})
		} else {

			user.ID = userID

			fmt.Printf("SAVED")

			ctx.Render("signup-success.html", nil)
		}
		ctx.JSON(200, user)
	}
}

在这次失败之后，我将Configure函数更改如下：

configure.go

func Configure() (Config *Configuration, err error) {

	if Config != nil {
		return
	}
}

并且我在处理程序中更改了使用方式。

handlers.go

config, err := Configure()

if err != nil {
	ctx.RenderWithStatus(iris.StatusBadRequest, "400.html", ErrorPageData{"try again later"})
	return
}

user := User{mail, password, 0}
db := config.Database

... 然后一切都开始完美地工作了。

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？

<details>
<summary>英文:</summary>

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.

I tried to build similar to this in go and failed horribly. 

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:



    2017/02/19 14:05:44 http: panic serving 127.0.0.1:53554: runtime error: invalid memory address or nil pointer dereference
        goroutine 50 [running]:
        net/http.(*conn).serve.func1(0xc42027c000)
            /usr/local/go/src/net/http/server.go:1491 +0x12a
        panic(0x9f45c0, 0xc42000c100)
            /usr/local/go/src/runtime/panic.go:458 +0x243
        main.SignUp(0xc4202780e0)
            /home/attila/dev/gopath/src/github.com/attilasatan/helloiris/handlers.go:31 +0x258
        github.com/kataras/iris.HandlerFunc.Serve(0xafaf00, 0xc4202780e0)
            /home/attila/dev/gopath/src/github.com/kataras/iris/http.go:211 +0x30
        github.com/kataras/iris.(*Context).Do(0xc4202780e0)
            /home/attila/dev/gopath/src/github.com/kataras/iris/context.go:152 +0x4d
        github.com/kataras/iris.(*serveMux).BuildHandler.func1(0xc4202780e0)
            /home/attila/dev/gopath/src/github.com/kataras/iris/http.go:1059 +0x6ea
        github.com/kataras/iris.(*Framework).Build.func1.1(0xd87e20, 0xc4202701a0, 0xc420284000)
            /home/attila/dev/gopath/src/github.com/kataras/iris/iris.go:411 +0x72
        net/http.HandlerFunc.ServeHTTP(0xc420235080, 0xd87e20, 0xc4202701a0, 0xc420284000)
            /usr/local/go/src/net/http/server.go:1726 +0x44
        net/http.serverHandler.ServeHTTP(0xc420089f80, 0xd87e20, 0xc4202701a0, 0xc420284000)
            /usr/local/go/src/net/http/server.go:2202 +0x7d
        net/http.(*conn).serve(0xc42027c000, 0xd88820, 0xc42015c200)
            /usr/local/go/src/net/http/server.go:1579 +0x4b7
        created by net/http.(*Server).Serve
            /usr/local/go/src/net/http/server.go:2293 +0x44d
        2017/02/19 14:05:44 http: panic serving 127.0.0.1:53560: runtime error: invalid memory address or nil pointer dereference
        goroutine 51 [running]:
        net/http.(*conn).serve.func1(0xc42027c180)
            /usr/local/go/src/net/http/server.go:1491 +0x12a
        panic(0x9f45c0, 0xc42000c100)
            /usr/local/go/src/runtime/panic.go:458 +0x243
        main.SignUp(0xc4202ac070)
            /home/attila/dev/gopath/src/github.com/attilasatan/helloiris/handlers.go:31 +0x258
        github.com/kataras/iris.HandlerFunc.Serve(0xafaf00, 0xc4202ac070)
            /home/attila/dev/gopath/src/github.com/kataras/iris/http.go:211 +0x30
        github.com/kataras/iris.(*Context).Do(0xc4202ac070)
            /home/attila/dev/gopath/src/github.com/kataras/iris/context.go:152 +0x4d
        github.com/kataras/iris.(*serveMux).BuildHandler.func1(0xc4202ac070)
            /home/attila/dev/gopath/src/github.com/kataras/iris/http.go:1059 +0x6ea
        github.com/kataras/iris.(*Framework).Build.func1.1(0xd87e20, 0xc4202a60d0, 0xc4202840f0)
            /home/attila/dev/gopath/src/github.com/kataras/iris/iris.go:411 +0x72
        net/http.HandlerFunc.ServeHTTP(0xc420235080, 0xd87e20, 0xc4202a60d0, 0xc4202840f0)
            /usr/local/go/src/net/http/server.go:1726 +0x44
        net/http.serverHandler.ServeHTTP(0xc420089f80, 0xd87e20, 0xc4202a60d0, 0xc4202840f0)
            /usr/local/go/src/net/http/server.go:2202 +0x7d
        net/http.(*conn).serve(0xc42027c180, 0xd88820, 0xc42015c480)
            /usr/local/go/src/net/http/server.go:1579 +0x4b7
        created by net/http.(*Server).Serve

Here is my configure file. As you can see I&#39;m using `tideland/golib/redis` for redis connection.

**configure.go**

	package main

	import (
		&quot;fmt&quot;
		&quot;strconv&quot;
		&quot;time&quot;

		&quot;github.com/tideland/golib/redis&quot;
	)

	/*Configuration is the main type of app configuration */
	type Configuration struct {
		Database *redis.Connection
	}

	/*Config is app configuration holder */
	var Config *Configuration

	/*Configure handles database connection */
	func Configure() (*Configuration, error) {

		db, err := redis.Open(redis.TcpConnection(&quot;127.0.0.1:6379&quot;, 30*time.Second))

		if err != nil {
			fmt.Printf(&quot;Database connection error&quot;)
			return nil, err
		}
		conn, err := db.Connection()

		n, _ := conn.DoInt(&quot;INCR&quot;, &quot;IDIDID&quot;)

		fmt.Printf(strconv.Itoa(n))

		if err != nil {
			fmt.Printf(&quot;Database connection error&quot;)
			return nil, err
		}

		/*Config is the main configuration object*/

		Config := &amp;Configuration{conn}

		return Config, err
	}

And here is where I use `Config.Database`. 

**handlers.go**

	func SignUp(ctx *iris.Context) {
		mail := ctx.FormValue(&quot;email&quot;)
		password := ctx.FormValue(&quot;password&quot;)
		passwordConfirm := ctx.FormValue(&quot;password-confirm&quot;)

		if password != passwordConfirm {
			ctx.RenderWithStatus(iris.StatusBadRequest, &quot;400.html&quot;, ErrorPageData{&quot;passwords dont match&quot;})
		} else {

			user := User{mail, password, 0}
			db := Config.Database

			userID, err := db.DoInt(&quot;INCR&quot;, &quot;HELLOIRIS:ID&quot;)

			if err != nil {
				ctx.RenderWithStatus(iris.StatusBadRequest, &quot;400.html&quot;, ErrorPageData{&quot;passwords dont match&quot;})
			} else {

				user.ID = userID
				
				fmt.Printf(&quot;SAVED&quot;)

				ctx.Render(&quot;signup-success.html&quot;, nil)
			}
			ctx.JSON(200, user)
		}
	}

After this fail I changed `Configure` function like this:

**configure.go**

    func Configure() (Config *Configuration, err error) {

    	if Config != nil {
		return
    	}
    }

and I changed the usage at handler  

**handlers.go**

    config, err := Configure()

	if err != nil {
		ctx.RenderWithStatus(iris.StatusBadRequest, &quot;400.html&quot;, ErrorPageData{&quot;try again later&quot;})
		return
	}

	user := User{mail, password, 0}
	db := config.Database

... and everything start to work perfectly.

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?


</details>


# 答案1
**得分**: 4

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。

<details>
<summary>英文:</summary>

    Config := &amp;Configuration{conn}

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.

</details>



# 答案2
**得分**: 1

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：

&gt; 运行时错误：无效的内存地址或nil指针解引用

请确保在你的`main`函数中调用`func Configure()`之前调用了处理程序。

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：

    Config = &amp;Configuration{conn}



  [1]: https://stackoverflow.com/a/42326810/2652524

<details>
<summary>英文:</summary>

You&#39;re getting this problem because your `Config` global variable is not set or still hold nil value. as the error said : 

&gt; runtime error: invalid memory address or nil pointer dereference

Make sure you called 
`func Configure()` before the handler called in your `main` function

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: 

    Config = &amp;Configuration{conn}



  [1]: https://stackoverflow.com/a/42326810/2652524

</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
  • go
  • pointers
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