Question

我无法以某种方式访问数组中的值。以下是声明数组的方式：

update record1
set id = 
  (select record2.id 
   from record2,record1 
   where record1.name=record2.name 
   and record1.weight<record2.weight)

但是当我对这个数组进行循环时，我得到空字符串作为值。这就是循环：

messages := strings.Split(request_string, end_of_message_terminator)

这就是输出：

for i, v := range messages {
    fmt.Printf("messages are (3) %q\n", messages)
    go func(){

        fmt.Printf("message is %s\n", messages[i])
        fmt.Printf("i is %s\n", i)
        fmt.Printf("v is %s\n", v)
        respond_to_message(messages[i], response_writer())
    }()


}

有谁知道问题是什么？为什么我可以访问此切片中的各个值？

如果您想运行此代码，以下是整个程序：

messages are (3) ["asti" ""]
messages are (3) ["asti" ""]
message is                  
i is %!s(int=1)             
v is                        
message is                  
i is %!s(int=1)             
v is

您需要先运行此程序：

package main


import (
    "fmt"
    "net"
    "os"
    "strings"
//  "io/ioutil"


)


func main() {

    end_of_message_terminator := "||"
    beginning_of_next_message := ""
    request := make([]byte, 512)

    service_port := ":7777"
    tcpAddr, err := net.ResolveTCPAddr("tcp4", service_port)
    checkError(err)
    listener, err := net.ListenTCP("tcp", tcpAddr)
    checkError(err)



    for {
        conn, err := listener.Accept()

        if err != nil {

            continue

        }

        read_len, err := conn.Read(request)

        if read_len == 0 {
            continue
        }

        request_string := string(request[:read_len])
        fmt.Printf("Request String '%s'\n", request_string)

        messages := strings.Split(request_string, end_of_message_terminator)
        fmt.Printf("messages are (1) %q\n", messages)

        messages[0] = beginning_of_next_message + messages[0]

        if messages[len(messages) - 1] != "" {
            beginning_of_next_message = messages[len(messages) - 1]
            messages[len(messages) - 1] = ""

        }

        if len(messages) == 1 {
            continue
        }

        fmt.Printf("messages are (2) %q\n", messages)
        for i, v := range messages {
            fmt.Printf("messages are (3) %q\n", messages)
            go func(){

                fmt.Printf("message is %s\n", messages[i])
                fmt.Printf("i is %s\n", i)
                fmt.Printf("v is %s\n", v)

            }()


        }
        conn.Close()

    }

}






func checkError(err error) {

    if err != nil {

        fmt.Fprintf(os.Stderr, "Fatal error: %s", err.Error())
        os.Exit(1)

    }

}

然后，最后（在启动此程序并运行netcat -l -p 8000之后），您需要运行：

netcat -l -p 8000

Answer 1

在你的goroutine中，你没有正确绑定i：

for i, v := range messages {
    fmt.Printf("messages are (3) %q\n", messages)
    go func(i int){

        fmt.Printf("message is %s\n", messages[i])
        fmt.Printf("i is %s\n", i)
        fmt.Printf("v is %s\n", v)
        respond_to_message(messages[i], response_writer())
    }(i) // you'll have to pass i here
}

您没有看到任何输出，因为每个i的值都设置为len(messages) - 1，在这种情况下为2 - 1 = 1且值为messages[1] == ""

所以每个goroutine都打印messages[1]这是一个空字符串。

去，麻烦迭代数组

1 个答案: