在 GO 中重用数据库连接和“无效内存地址”错误

Question

我是 GO 新手，似乎无法找到有关在全局中重用数据库连接的错误的任何信息。这是导致错误的代码的简化版本：包主import (    _ "github.com/denisenkom/go-mssqldb"    "database/sql")var debug = flag.Bool("debug", false, "enable debugging")var password = flag.String("password", "*****", "the database password")var port *int = flag.Int("port", 1433, "the database port")var server = flag.String("server", "localhost", "the database server")var user = flag.String("user", "*****", "the database user")var db *sql.DBfunc main() {    // Parse the incoming flags to set variables.    flag.Parse()    // Output the database variables if the debug flag is set.    if *debug {        fmt.Printf(" password:%s\n", *password)        fmt.Printf(" port:%d\n", *port)        fmt.Printf(" server:%s\n", *server)        fmt.Printf(" user:%s\n", *user)    }    // Build out the connection string to the database, and then open the connection to the database.    connString := fmt.Sprintf("server=%s;user id=%s;password=%s;port=%d", *server, *user, *password, *port)    if *debug { fmt.Printf(" connString:%s\n", connString) }    db, err := sql.Open("mssql", connString)    if err != nil { log.Fatal("Open connection failed:", err.Error()) }    err = db.Ping()    if err != nil {        fmt.Println("Cannot connect: ", err.Error())        return    }    // Close the connection when we're all done.    defer db.Close()    // Truncate the existing records in the ListHubFeed    res, err := db.Exec( `        TRUNCATE TABLE foo    ` )    _ = res    if err != nil {        fmt.Println( "TRUNCATE TABLE failed", err )    }    eligible := verifyEligibility( "foo" )}func verifyEligibility( email string ) ( success bool ) {    //Run each check individually, and if any one fails, return false and stop processing additional checks    // if the routing email is bad, then we can't create an account, so kick it out.    if( !govalidator.IsEmail( email ) ){        writeToLog( email )        return false    }    return true;}

Answer 1

你的问题是db指针nil在你的writeToLog()函数的上下文中。罪魁祸首是这一行：

db, err := sql.Open("mssql", connString)

在这里，您将短变量声明运算符 ( :=) 与赋值运算符 ( =)混淆了。

此指令db使用db局部变量覆盖全局变量，只能在您的main函数中访问（这称为shadowing，也适用于包名称等）。因此，使用的db变量writeToLog永远不会被初始化，因此是nil pointer dereference错误的。

要修复它，您只需要修复您的声明，使其成为做作：

var err error

db, err = sql.Open("mssql", connString)