CODEWITHSUNDEEP
go
Said Saifi
Said Saifi

Reputation: 2408

How can I log the value of a pointer if it is not nil, otherwise log nil in GO?

Hi I want to log the value of a variable if it is not nil otherwise I want to print anything else

for example:

var point *string
var point2 *string

p:="hi"

point2=&p

fmt.Printf("%v,%v",*point,*point2)

in this case I will have an error since point is nill, so is there any way to print the value of the variable if it is not nil or print anything else if it is nil?

I want to do this in a simple way instead of creating an if/else statement to check if the variable is nil

Upvotes: 9

Views: 6301

Answers (4)

Cpt.Ohlund
Cpt.Ohlund

Reputation: 2679

I can recommend using https://github.com/samber/lo

Among other useful functions there is FromPtrOr:

str := "hello world"
value := lo.FromPtrOr(&str, "empty")
// "hello world"

value := lo.FromPtrOr[string](nil, "empty")
// "empty"

Upvotes: 1

Feckmore
Feckmore

Reputation: 4734

For a more general way to log out values of pointers or even pointers within structs you can marshal to JSON and log the results.

Here's an example that prints individual pointer & non-pointer values, as well as a struct using this method.

type Line struct {
    Point1 *string
    Point2 *string
    Name   string
}

func main() {
    point1 := "one"
    line := Line{&point1, nil, "fancy"}

    printJSON(line.Point1, line.Point2, line.Name)
    printJSON(line)
}

func printJSON(i ...interface{}) {
    if b, err := json.Marshal(i); err == nil {
        log.Println(string(b))
    }
}

Go Playground

Upvotes: 2

nosequeldeebee
nosequeldeebee

Reputation: 963

You should probably use if/else in this case BUT if you have many potential "if" conditions for each of point and point2 you can use Switch statements.

package main

import (
    "fmt"
)

func main() {

    type Points struct {
        Point  *string
        Point2 *string
    }

    p := "hi"
    pts := Points{nil, &p}

    switch pts.Point {
    case nil:
        fmt.Printf("%v is empty", pts.Point)
    default:
        fmt.Printf("%v", *pts.Point)

    }

    fmt.Println()

    switch pts.Point2 {
    case nil:
        fmt.Printf("%v is empty", pts.Point2)
    default:
        fmt.Printf("%v", *pts.Point2)

    }

}

Output:

<nil> is empty
hi

Go playground

Upvotes: 1

Roland Illig
Roland Illig

Reputation: 41686

Since there is no ?: operator in Go, the best way is to write a function:

func StringPtrToString(p *string) string {
    if p != nil { return *p }
    return "(nil)"
}

Upvotes: 1

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