Error in importing custom packages in Go Lang

I have created a library by the name libfastget which is in the src with my program as

src
|-libfastget
|  |-libfastget.go
|
|-MainProgram
   |-main.go

and the libfastget exports a funtion fastget as follows

package libfastget

import (
    "fmt"
    "io"

)


func fastget(urlPtr *string, nPtr *int, outFilePtr *string) download {
    .....
    return dl

}

When I use the library in my main program

package main

import (
    "fmt"
    "net/http"
    "os"
    "libfastget"
    "path/filepath"
    "strings"
    "flag"
    "time"

)
func uploadFunc(w http.ResponseWriter, r *http.Request) {

         n:=libfastget.fastget(url,4,filename)

    }

}

I get the following error upon trying to build with go build

# FServe
./main.go:94: cannot refer to unexported name libfastget.fastget
./main.go:94: undefined: libfastget.fastget

The strange thing is that the library file libfastget.a is present in the pkg folder.

you would need to make your function exportable with an uppercase for its name:

func Fastget(...

Used as:

n:=libfastget.Fastget(url,4,filename)

The spec mentions: "Exported identifiers":

An identifier may be exported to permit access to it from another package. An identifier is exported if both:

the first character of the identifier's name is a Unicode upper case letter (Unicode class "Lu"); and
the identifier is declared in the package block or it is a field name or method name.

All other identifiers are not exported.

I recently started learning GO Lang (2 days back) And what I found was you need to setup a workspace folder to make the local packages import into other projects or main.go files. I'm using VS Code editor. Please correct me if Im wrong, but this setup works fine for me.

Inside your bash_profile OR .zshrc file add below lines, update the GOPATH as per your folder path.

export GOPATH=~/projects/GO_PROJECTS
export PATH=$PATH:$GOPATH/bin:$PATH

and this is my sayHello.go file, please note to be able to export a function the func name should start with a CapitalCase SayHello

package utils

import "fmt"

func SayHello() {
    fmt.Println("Hello, Ajinkya")
}

and now I am able to import utils package into main.go file

package main

import (
    "go_proj1/utils"
)

func main() {
    utils.SayHello()
}

set the current directory as GOPATH
or you can use local import as follows

move your main.go to the ../ directory to the libfastget.go.
i mean the files looks like:
src
|-libfastget
| |-libfastget.go
|
|-main.go

import "./libfastget"

来源：https://stackoverflow.com/questions/25501875/error-in-importing-custom-packages-in-go-lang

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