Will glog content been executed if does not meet required level

The question is simple, I have a log like this:

glog.v(5).Infof("xxx %v", getLogContent())

But my getLogContent() is a time consuming method, so I want to ask: will getLogContent() been executed or not when my program does not meet v(5) level?

Yes.

You should add an if statement if you don't want getLogContent() to run

if glog.V(5) {
    glog.V(5).Infof("xxx %v", getLogContent())
}

Go evaluates all arguments, so getLogContent will get called but the output will not be logged if the verbosity level has not been met.

I was curious and playing around with this. I don't know if this would work for you but it's interesting.

By using a lambda function, and making a function type that implements the Stringer interface, the Go format library will call it when it needs to print it.

I could not find a way I really liked to create the function type, maybe someone else knows some better trick.

package main

import (
	"fmt"
	"os"
	"time"
)

type thing func() string

func (t thing) String() string {
	return t()
}

func toThing(f func() string) thing {
	return f
}

func maybePrint(p bool, args ...interface{}) {
	if p {
		fmt.Println(args...)
	}
}

func main() {
	maybePrint(len(os.Args) > 2, "testing", toThing(func() string {
		fmt.Println("Calculating big thing")
		time.Sleep(time.Second)
		return "test"
	}))
}