为什么我无法在Go中将指针字符串转换为字符串？

Question

This code parse command-line arguments. If I type "/netstat -c /etc/config -I eth0", it should is :" c /etc/config i eth0", but it's not . Terminal output is :

c configfile

c interface

./netstat -c /etc/config -i eth0
c configfile
c interface

Code is as below:

package main

import (
    "flag"
    "fmt"
)

type CmdSt struct {
    configPtr    string
    interfacePtr string
}

var cmdSt CmdSt

func usage() {

    cmdSt.configPtr = *flag.String("c", "configfile", "configure file to parse ")
    cmdSt.interfacePtr = *flag.String("i", "interface", "capture network interface")
    /*
        a := flag.String("c", "configfile", "configure file to parse ")
        b := flag.String("i", "interface", "capture network interface")
    */

    flag.Parse()

    fmt.Println("c", cmdSt.configPtr)
    fmt.Println("i", cmdSt.interfacePtr)
    /*
        fmt.Println("c:", *a)
        fmt.Println("i:", *b)
    */
}
func main() {
    usage()

}

Answer 1

It is because you're still holding the default value before flag.Parse() is called:

// still holding the "configfile" as value
cmdSt.configPtr = *flag.String("c", "configfile", "configure file to parse ")
// still holding the "interface" as value
cmdSt.interfacePtr = *flag.String("i", "interface", "capture network interface")

// flag is parsed now, but both cmdSt.configPtr and cmdSt.interfacePtr still holding the default value because of the pointer.
flag.Parse()

You can solve the problem by using temporary variables:

// hold the value to temporary variables
a := flag.String("c", "configfile", "configure file to parse ")
b := flag.String("i", "interface", "capture network interface")

// parse the flag and save to the variables.
flag.Parse()

// now, point the value to the CmdSt struct
cmdSt.configPtr = *a
cmdSt.interfacePtr = *b


fmt.Println("c", cmdSt.configPtr)
fmt.Println("i", cmdSt.interfacePtr)