如何在Go中设置和访问“全局”记录器？

Question

I am sure there's some simple, fundamental issue I'm missing, I'm very new to go. How do I set up a logger so it can be shared between functions, assuming I do not want to use the default logger?

logissue.go

package main

import (
  "fmt"
  "github.com/pkg/errors"
  "log"
  "os"
)

var dlog log.Logger

const logfile string = "killer.log"
const logprefix string = "LOGTEST: "

func setupLogger(filename, prefix string) (*log.Logger, error) {
  out, err := os.OpenFile(filename, os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0644)
  if err != nil {
    return nil, errors.Wrap(err, "can't open logfile for writing")
  }
  return log.New(out, prefix, log.LstdFlags), nil
}

func uselog() error {
  fmt.Printf("%T
", dlog)
  dlog.Printf("Hello")            ///// < Here is the issue
  return nil
}

func main() {
  dlog, err := setupLogger(logfile, logprefix)
  if err != nil {
    fmt.Printf("%+v", err)
  }
  dlog.Printf("test from main")
  uselog()
}

stdout

log.Logger
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x18 pc=0x10970b8]

goroutine 1 [running]:
log.(*Logger).Output(0x116dd00, 0x2, 0xc000016106, 0x5, 0x0, 0x0)
    /usr/local/go/src/log/log.go:172 +0x1e8
log.(*Logger).Printf(0x116dd00, 0x10c9202, 0x5, 0x0, 0x0, 0x0)
    /usr/local/go/src/log/log.go:179 +0x7e
main.uselog(0xc000088050, 0x10ca43b)
    /Users/sequoia/learning/Ex_Files_Go_EssT/Exercise Files/logissue.go:25 +0xc4
main.main()
    /Users/sequoia/learning/Ex_Files_Go_EssT/Exercise Files/logissue.go:35 +0xee
exit status 2

killer.log

LOGTEST: 2019/02/17 18:25:12 test from main

Answer 1

So first of all based on your code above you're trying to set a non-pointer logger with a pointer logger which wont work. Secondly you're using := when setting dlog which creates a scoped variable in your main method rather than setting your global variable