How to properly output a string in a Windows console with go?

Question

I have a exe in go which prints utf-8 encoded strings, with special characters in it.
Since that exe is made to be used from a console window, its output is

Answer 1

It is something that Go still can't do out of the box - see http://code.google.com/p/go/issues/detail?id=3376#c6.

Alex

Answer 2

// Alert: This is Windows-specific, uses undocumented methods, does not
// handle stdout redirection, does not check for errors, etc.
// Use at your own risk.
// Tested with Go 1.0.2-windows-amd64.

package main

import "unicode/utf16"
import "syscall"
import "unsafe"

var modkernel32 = syscall.NewLazyDLL("kernel32.dll")
var procWriteConsoleW = modkernel32.NewProc("WriteConsoleW")

func consolePrintString(strUtf8 string) {
    var strUtf16 []uint16
    var charsWritten *uint32

    strUtf16 = utf16.Encode([]rune(strUtf8))
    if len(strUtf16) < 1 {
        return
    }

    syscall.Syscall6(procWriteConsoleW.Addr(), 5,
        uintptr(syscall.Stdout),
        uintptr(unsafe.Pointer(&strUtf16[0])),
        uintptr(len(strUtf16)),
        uintptr(unsafe.Pointer(charsWritten)),
        uintptr(0),
        0)
}

func main() {
    consolePrintString("Hello ☺\n")
    consolePrintString("éèïöîôùòèìë\n")
}

Answer 3

Since 2016, You can now (2017) consider the golang.org/x/text, which comes with a encoding charmap including the ISO-8859 family as well as the Windows 1252 character set.

See "Go Quickly - Converting Character Encodings In Golang"

r := charmap.ISO8859_1.NewDecoder().Reader(f)
io.Copy(out, r)

That is an extract of an example opening a ISO-8859-1 source text (my_isotext.txt), creating a destination file (my_utf.txt), and copying the first to the second.
But to decode from ISO-8859-1 to UTF-8, we wrap the original file reader (f) with a decoder.

I just tested (pseudo-code for illustration):

package main

import (
    "fmt"

    "golang.org/x/text/encoding"
    "golang.org/x/text/encoding/charmap"
)

func main() {
    t := "string composed of character in cp 850"
    d := charmap.CodePage850.NewDecoder()
    st, err := d.String(t)
    if err != nil {
        panic(err)
    }
    fmt.Println(st)
}

The result is a string readable in a Windows CMD.
See more in this Nov. 2018 reddit thread.

Answer 4

The online book "Network programming with Go" (CC BY-NC-SA 3.0) has a chapter on Charsets (Managing character sets and encodings), in which Jan Newmarch details the conversion of one charset to another. But it seems cumbersome.

Here is a solution (I might have missed a much simpler one), using the library go-charset (from Roger Peppe).
I translate an utf-8 string to an ibm850 encoded one, allowing me to print in a DOS windows:

éèïöîôùòèìë

The translation function is detailed below:

package main

import (
    "bytes"
    "code.google.com/p/go-charset/charset"
    _ "code.google.com/p/go-charset/data"
    "fmt"
    "io"
    "log"
    "strings"
)

func translate(tr charset.Translator, in string) (string, error) {
    var buf bytes.Buffer
    r := charset.NewTranslatingReader(strings.NewReader(in), tr)
    _, err := io.Copy(&buf, r)
    if err != nil {
        return "", err
    }
    return string(buf.Bytes()), nil
}

func Utf2dos(in string) string {
    dosCharset := "ibm850"
    cs := charset.Info(dosCharset)
    if cs == nil {
        log.Fatal("no info found for %q", dosCharset)
    }
    fromtr, err := charset.TranslatorTo(dosCharset)
    if err != nil {
        log.Fatal("error making translator from %q: %v", dosCharset, err)
    }
    out, err := translate(fromtr, in)
    if err != nil {
        log.Fatal("error translating from %q: %v", dosCharset, err)
    }
    return out
}

func main() {
    test := "éèïöîôùòèìë"
    fmt.Println("utf-8:\n", test)
    fmt.Println("ibm850:\n", Utf2dos(test))
}