Golang : Dealing with postal or zip code example

Problem :

For some countries, the postal code or zip code starts with zero and this can be problematic for developers. Quite frequently, programmers will assume that the postal or zip code is in integer type and this is will introduce funky bugs later on. Why? because leading zero in integer will the turn the variable/constant value to become Octal value and thus screw up the final value.

Solution :

The code below will simulate a zip code input with leading zero and type integer. It will demonstrate the problem and show you how to fix it.

 package main

 import (

 func main() {

 //leading zero will convert zip code to octal!
  var iZip = 0000123 
  fmt.Println("No longer int, but octal value : ", iZip) //funky value
  fmt.Printf("Type : %v \n", reflect.TypeOf(iZip))


  // do not use this method as the leading zero will disappear!

  zip := strconv.FormatInt(int64(iZip), 8) // base 8 for Octal
  fmt.Println("Wrong! Don't use this method because of : ")
  fmt.Println("Missing zero : ", zip)
  fmt.Printf("Type : %v \n", reflect.TypeOf(zip))


  // always convert zip code to type string before display!

  // calculate the size of the iZip octal - the wrong way!
  t := reflect.TypeOf(iZip)
  fmt.Println("Type : ", t)
  // play.golang.org return 4
  // go run will return 8 bytes - not to be trusted for now
  fmt.Println("Size : ", t.Size()) 

  // pad zero up to the length of 7, o is for expecting octal value
  newZip := fmt.Sprintf("0000%o", iZip)

  // ** NOTE : Have to hardcode 7 because there is no way
  // I can programmatically insert the t.Size()-1 into fmt.Sprintf()

  fmt.Println("Converted from integer to string : ", newZip)
  fmt.Printf("Type : %v \n", reflect.TypeOf(newZip))

Output :

No longer int, but octal value : 83

Type : int


Wrong! Don't use this method because of :

Missing zero : 123

Type : string


Converted from integer to string : 0000123

Type : string

By Adam Ng

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