go 调用windows dll 的三种方法

参考：https://blog.csdn.net/qq_39584315/article/details/81287669

大部分代码参考：https://studygolang.com/articles/2712

第三种方法是从Go\src\internal\syscall\windows\sysdll源码中找到的，三种方法的具体区别还不是很明晰，

初步判断：lazy应该是相当于动态库，其余两种直接把库加载到内存。

package main

import (
    "fmt"
    "syscall"
    "time"
    "unsafe"
)

const (
    MB_OK                = 0x00000000
    MB_OKCANCEL          = 0x00000001
    MB_ABORTRETRYIGNORE  = 0x00000002
    MB_YESNOCANCEL       = 0x00000003
    MB_YESNO             = 0x00000004
    MB_RETRYCANCEL       = 0x00000005
    MB_CANCELTRYCONTINUE = 0x00000006
    MB_ICONHAND          = 0x00000010
    MB_ICONQUESTION      = 0x00000020
    MB_ICONEXCLAMATION   = 0x00000030
    MB_ICONASTERISK      = 0x00000040
    MB_USERICON          = 0x00000080
    MB_ICONWARNING       = MB_ICONEXCLAMATION
    MB_ICONERROR         = MB_ICONHAND
    MB_ICONINFORMATION   = MB_ICONASTERISK
    MB_ICONSTOP          = MB_ICONHAND

    MB_DEFBUTTON1 = 0x00000000
    MB_DEFBUTTON2 = 0x00000100
    MB_DEFBUTTON3 = 0x00000200
    MB_DEFBUTTON4 = 0x00000300
)

func abort(funcname string, err syscall.Errno) {
    panic(funcname + " failed: " + err.Error())
}

var (
    user32, _     = syscall.LoadLibrary("user32.dll")
    messageBox, _ = syscall.GetProcAddress(user32, "MessageBoxW")
)

func IntPtr(n int) uintptr {
    return uintptr(n)
}

func StrPtr(s string) uintptr {
    return uintptr(unsafe.Pointer(syscall.StringToUTF16Ptr(s)))
}

func MessageBox(caption, text string, style uintptr) (result int) {
    ret, _, callErr := syscall.Syscall9(messageBox,
        ,
        ,
        StrPtr(text),
        StrPtr(caption),
        style,
        , , , , )
    if callErr !=  {
        abort("Call MessageBox", callErr)
    }
    result = int(ret)
    return
}

//func GetModuleHandle() (handle uintptr) {
//    if ret, _, callErr := syscall.Syscall(getModuleHandle, 0, 0, 0, 0); callErr != 0 {
//        abort("Call GetModuleHandle", callErr)
//    } else {
//        handle = ret
//    }
//    return
//}

// windows下的第二种DLL方法调用
func ShowMessage2(title, text string) {
    user32 := syscall.NewLazyDLL("user32.dll")
    MessageBoxW := user32.NewProc("MessageBoxW")
    MessageBoxW.Call(IntPtr(), StrPtr(text), StrPtr(title), IntPtr())
}

// windows下的第三种DLL方法调用
func ShowMessage3(title, text string) {
    user32, _ := syscall.LoadDLL("user32.dll")
    MessageBoxW, _ := user32.FindProc("MessageBoxW")
    MessageBoxW.Call(IntPtr(), StrPtr(text), StrPtr(title), IntPtr())
}

func main() {
    defer syscall.FreeLibrary(user32)

    num := MessageBox("Done Title", "This test is Done.", MB_YESNOCANCEL)
    fmt.Printf("Get Retrun Value Before MessageBox Invoked: %d\n", num)
    ShowMessage2("windows下的另一种DLL方法调用", "HELLO !")

    ShowMessage3("windows下的第三种DLL方法调用", "lyslyslys !")

    time.Sleep( * time.Second)
}

func init() {
    fmt.Print("Starting Up\n")
}