为什么我的全局变量没有跨包设置？ [重复]

Question

This question already has an answer here:

• How to access global variables 3 answers

I have the following code:

main.go:

package main

import (
    "fmt"

    "./globalvar"

    "github.com/Denton-L/gotest/usevar"
)

func main() {
    globalvar.GlobalNum = 42
    fmt.Println(globalvar.GlobalNum)
    usevar.PrintGlobal()
}

usevar/usevar.go:

package usevar

import (
    "fmt"

    "github.com/Denton-L/gotest/globalvar"
)

func PrintGlobal() {
    fmt.Println(globalvar.GlobalNum)
}

globalvar/globalvar.go:

package globalvar

var GlobalNum int

and I'm compiling with go build main.go. When I run ./main, I get

42
0

as output but I am expecting

42
42

Why is this happening?

EDIT: Note that I'm able to access the global variables but they contain unexpected values so this is not a duplicate of Golang Global Variable access.

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Answer 1

The reason why this is happening is because we're mixing relative and remote imports. In main.go, the globalvar package is imported as ./globalvar but usevar/usevar.go imports it as github.com/Denton-L/gotest/globalvar. Therefore, Go considers these to be separate packages with their own namespaces and thus, they have their own separate global variables that happen to be named identically.

In order to solve this, change the relative import to be a remote import, so the main.go import statement should look like this:

import (
    "fmt"

    "github.com/Denton-L/gotest/globalvar"
    "github.com/Denton-L/gotest/usevar"
)

This will let the compiler know that they are actually the same package and, thus, the global variable will be shared.