Why Can\'t My Go Application Print to the Console When Compiled with `-ldflags -H=windowsgui`?

Printing Output with -H=windowsgui Flag

When compiling a Go application with the -ldflags -H=windowsgui flag, it may not be able to print output to a command window. This is because the executable is created as a GUI process that is not associated with any console, even when invoked from the console.

To print output in this scenario, one must explicitly attach the process to the console. This can be achieved using the syscall package:

package main

import (
    "fmt"
    "syscall"
)

const (
    ATTACH_PARENT_PROCESS = ^uint32(0)
)

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("Attached")
    }
}

By invoking AttachConsole(ATTACH_PARENT_PROCESS), the Go process is attached to the console associated with its parent process. It can then print output to the console.

If AttachConsole fails, it may be necessary to create a console window manually using AllocConsole or display a GUI dialog with the desired information using appropriate GUI libraries.

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