How Can Go GUI Applications Print to the Command Window?

Printing Output to the Command Window with Windows GUI Linked Go Applications

When compiling Go applications with the -ldflags -H=windowsgui flag, the resulting executable is set to run as a Windows GUI application. By default, GUI applications do not have access to the console, preventing the output of printed strings.

To address this issue, the syscall package can be used to explicitly attach the GUI process to its parent's console. This allows the application to print output to the command window:

package main

import (
    "fmt"
    "syscall"
)

const (
    ATTACH_PARENT_PROCESS = ^uint32(0) // (DWORD)-1
)

var (
    modkernel32 = syscall.NewLazyDLL("kernel32.dll")

    procAttachConsole = modkernel32.NewProc("AttachConsole")

)

func AttachConsole(dwParentProcess uint32) (ok bool) {
    r0, _, _ := syscall.Syscall(procAttachConsole.Addr(), 1, uintptr(dwParentProcess), 0, 0)
    ok = bool(r0 != 0)
    return
}

func main() {
    ok := AttachConsole(ATTACH_PARENT_PROCESS)
    if ok {
        fmt.Println("Okay, attached")
    }
}

After attaching to the parent's console, the application can print output using the standard fmt.Println() function or directly writing to syscall.Stdout. However, if AttachConsole() fails, the application should either:

• Create its own console window using AllocConsole().
• Display the output in a GUI dialog.

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