I’m running into the same issue regarding printf if I follow writing out the code as it is shown in the book.

I tried looking up the official documentation to see where printf is defined and the docs have dead links.
https://scala-native.readthedocs.io/en/v0.3.9-docs/lib/libc.html

Dead link:
https://github.com/scala-native/scala-native/blob/master/nativelib/src/main/scala/scala/scalanative/native/stdlib.scala

Real link:

So nativelib was renamed to clib. So to be fair, scala-native is v0.3.9 and not stabilised yet so these quirks are part of the territory for bleeding edge.

Circling back to the pragprog listing though, I downloaded the latest source code which adds a compat.scala file which remaps printf to vprintf.

package scala.scalanative
import scalanative.unsafe._
import scalanative.libc.stdio

package object libc {
  implicit class StdioHelpers(val _stdio: libc.stdio.type) extends AnyVal {
    def printf(format: CString, args: CVarArg*): CInt =
      Zone { implicit z =>
        stdio.vprintf(format, toCVarArgList(args.toSeq))
      }

// Other unrelated code truncated

   }
}

If I download the source from:
http://media.pragprog.com/titles/rwscala/code/rwscala-code.zip

Extract it.

Then cd into code/InputAndOutput/hello_native and run sbt run it works.

Also I thought it was a typo between the “hello” and “hello_native” projects but it seems like capitalising the object name Main is important when linking.

hello/hello.scala

object main { 
  def main(args:Array[String]) { 
    println("hello, world!")
  }
}

hello_native/hello.scala

import scala.scalanative.unsafe._
import scala.scalanative.libc._

object Main {
  def main(args: Array[String]): Unit = {
    stdio.printf(c"Hello native %s!\n", c"world")
  }
}

After some digging it seems you can use vprintf directly using the following snippet:

import scala.scalanative.unsafe._
import scala.scalanative.libc._

object Main {
  def main(args: Array[String]) {
    Zone { implicit z =>
      stdio.vprintf(c"Hello native %s!\n", toCVarArgList(c"world"))
    }
  }
}

Using vprintf gave me the error “Given method requires an implicit zone”.

https://scala-native.readthedocs.io/en/v0.3.9-docs/user/interop.html#memory-management

Adding the Zone { implicit z => ..... } creates a section of code to help with unmanaged memory allocations like our CVarArgList.