频繁发生的运行时错误：无效的内存地址或零指针取消引用

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我对 golang 很陌生，并且大多数情况下都不知道到目前为止我在做什么。我尝试运行一个简单的 find() 查询来从我的数据库中获取所有文档，但我似乎无法让它工作，我不断收到此错误

panic: runtime error: invalid memory address or nil pointer dereference
[signal sigsegv: segmentation violation code=0x1 addr=0x58 pc=0x9e2623]

goroutine 40 [running]:
go.mongodb.org/mongo-driver/mongo.(*collection).find(0x0, 0xf9f2a0, 0xc0000a4008, 0xc07dc0, 0xc00034e1b0, 0x0, 0x0, 0x0, 0x42eda1, 0xcf4758, ...)
    /home/rashad/go/pkg/mod/go.mongodb.org/[email protected]/mongo/collection.go:1106 +0x63
github.com/rashadarbab/goserver/routes.getall(0xc000432000, 0x0, 0x0)
    /home/rashad/goserver/routes/handler.go:22 +0xf1
github.com/gofiber/fiber/v2.(*app).next(0xc0003ea000, 0xc000432000, 0x60b8d06b, 0x1da784f8, 0x9bd981defeb4)
    /home/rashad/go/pkg/mod/github.com/gofiber/fiber/[email protected]/router.go:127 +0x1b0
github.com/gofiber/fiber/v2.(*ctx).next(0xc000432000, 0x1feb2696b, 0x14d7d20)
    /home/rashad/go/pkg/mod/github.com/gofiber/fiber/[email protected]/ctx.go:656 +0x88
github.com/gofiber/fiber/v2/middleware/logger.new.func2(0xc000432000, 0xc000342208, 0x4)
    /home/rashad/go/pkg/mod/github.com/gofiber/fiber/[email protected]/middleware/logger/logger.go:155 +0x13f
github.com/gofiber/fiber/v2.(*app).next(0xc0003ea000, 0xc000432000, 0x0, 0xc0003221e0, 0x14f6240)
    /home/rashad/go/pkg/mod/github.com/gofiber/fiber/[email protected]/router.go:127 +0x1b0
github.com/gofiber/fiber/v2.(*ctx).next(0xc000432000, 0x0, 0x0)
    /home/rashad/go/pkg/mod/github.com/gofiber/fiber/[email protected]/ctx.go:656 +0x88
github.com/gofiber/fiber/v2.(*app).registerstatic.func3(0xc000432000, 0xc000342208, 0x4)
    /home/rashad/go/pkg/mod/github.com/gofiber/fiber/[email protected]/router.go:380 +0x180
github.com/gofiber/fiber/v2.(*app).next(0xc0003ea000, 0xc000432000, 0xc000432000, 0x1da63ae5, 0x1da63ae500000004)
    /home/rashad/go/pkg/mod/github.com/gofiber/fiber/[email protected]/router.go:127 +0x1b0
github.com/gofiber/fiber/v2.(*app).handler(0xc0003ea000, 0xc000424000)
    /home/rashad/go/pkg/mod/github.com/gofiber/fiber/[email protected]/router.go:155 +0x118
github.com/valyala/fasthttp.(*server).serveconn(0xc0003ec000, 0xfa5940, 0xc00032a008, 0x0, 0x0)
    /home/rashad/go/pkg/mod/github.com/valyala/[email protected]/server.go:2219 +0x1497
github.com/valyala/fasthttp.(*workerpool).workerfunc(0xc0003ee140, 0xc000322140)
    /home/rashad/go/pkg/mod/github.com/valyala/[email protected]/workerpool.go:223 +0xc0
github.com/valyala/fasthttp.(*workerpool).getch.func1(0xc0003ee140, 0xc000322140, 0xba7ae0, 0xc000322140)
    /home/rashad/go/pkg/mod/github.com/valyala/[email protected]/workerpool.go:195 +0x35
created by github.com/valyala/fasthttp.(*workerpool).getch
    /home/rashad/go/pkg/mod/github.com/valyala/[email protected]/workerpool.go:194 +0x101

我通过了检查点 1，并在检查点 2 之前卡住了。一切似乎都正常，我可以连接到数据库并对其进行 ping 操作以确保连接成功，但是当我从中获取一些数据时，它会抛出异常恐慌。

这里是一些相关的代码

（我正在尝试 ping handler.go 中的 getall() 函数）

处理程序.go

package routes

import (
    "context"
    "encoding/json"
    "fmt"
    "log"

    "github.com/rashadarbab/goserver/database"
    "github.com/gofiber/fiber/v2"
    "go.mongodb.org/mongo-driver/bson"
)

var db = database.db
var ctx = context.todo()

func getall(c *fiber.ctx) error {

    fmt.println("checkpoint 1")
    var users []database.user

    

    cursor, err := db.find(ctx, bson.m{})
    if err != nil {
        log.fatal(err)
    }

    fmt.println("checkpoint 2")

    // close the cursor once finished
    /*a defer statement defers the execution of a function until the surrounding function returns.
    simply, run cur.close() process but after cur.next() finished.*/

    defer cursor.close(context.todo())
    fmt.println("checkpoint 3")

    for cursor.next(context.todo()) {

        // create a value into which the single document can be decoded
        var user database.user
        // & character returns the memory address of the following variable.
        err := cursor.decode(&user) // decode similar to deserialize process.
        if err != nil {
            log.fatal(err)
        }

        // add item our array
        users = append(users, user)
    }

    fmt.println("checkpoint 4")

    documents, _ := json.marshal(users)
    return c.json(documents)

}

func createprod(c *fiber.ctx) error {
    return c.sendstring("this is create product")
}

func getsingle(c *fiber.ctx) error {
    id := c.params("id")
    return c.sendstring("this is create singular" + id)
}

main.go

package main

import (
    "github.com/rashadarbab/goserver/database"
    "github.com/rashadarbab/goserver/routes"

    "github.com/gofiber/fiber/v2"
)

func main() {
    database.init()

    app := fiber.new()

    app.static("/", "./aa-frontend/build")

    app.get("/", func(c *fiber.ctx) error {
        return c.sendstring("hello there")
    })

    routes.setuproutes(app)

    app.listen(":5000")
}

数据库.go

package Database

import (
    "go.mongodb.org/mongo-driver/mongo"
    "go.mongodb.org/mongo-driver/mongo/options"

    "context"
    "fmt"
    "log"
)

var DB *mongo.Collection
var ctx = context.TODO()

func Init() *mongo.Collection {
    clientOptions := options.Client().ApplyURI("mongodb://localhost:27017/")
    client, err := mongo.Connect(ctx, clientOptions)
    if err != nil {
        log.Fatal(err)
    }
    err = client.Ping(ctx, nil)
    if err != nil {
        log.Fatal(err)
    } else {
        fmt.Println()
    }

    DB = client.Database("GoServer").Collection("users")
    fmt.Print(DB.Name())

    return DB
}

正确答案

DB 为 nil，因为 var DB=database.DB 在 database.DB 初始化之前运行。

直接使用database.DB。

理论要掌握，实操不能落！以上关于《频繁发生的运行时错误：无效的内存地址或零指针取消引用》的详细介绍，大家都掌握了吧！如果想要继续提升自己的能力，那么就来关注golang学习网公众号吧！