golang调用DLL中的函数

在golang中加载dll并调用函数流程如下：
1.加载dll动态库到内存 syscall.LoadLibrary
2.获取函数地址 syscall.GetProcAddress
3.执行系统调用，传入参数 syscall.Syscall6

一个系统消息框函数的调用示例：

/**
动态加载dll并调用dll的函数
调用MessageBox函数
*/
func MessageBox(content, title string) uintptr {
    var user32, _ = syscall.LoadLibrary("user32.dll")
    defer syscall.FreeLibrary(user32)
    var msgbox, _ = syscall.GetProcAddress(user32, "MessageBoxW")

    //消息框样式常量定义
    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
    )
    /*
        int MessageBoxW(
          HWND    hWnd,
          LPCWSTR lpText,
          LPCWSTR lpCaption,
          UINT    uType
        );
    */

    //消息框MessageBoxA函数参数个数
    var argCount = uintptr(4)
    //消息框样式
    var uType = uintptr(MB_OK | MB_ICONWARNING | MB_CANCELTRYCONTINUE)
    //消息框内容
    var text, _ = syscall.UTF16PtrFromString(content)
    var lpText = uintptr(unsafe.Pointer(text))
    //消息框标题
    var caption, _ = syscall.UTF16PtrFromString(title)
    var lpCaption = uintptr(unsafe.Pointer(caption))

    var msgboxID, _, err = syscall.Syscall6(msgbox, argCount, 0, lpText, lpCaption, uType, 0, 0)
    if err != 0 {
        println(err)
        return 0
    }
    return msgboxID
}

func main() {
    const (
        IDABORT    = 3
        IDCANCEL   = 2
        IDCONTINUE = 11
        IDIGNORE   = 5
        IDNO       = 7
        IDOK       = 1
        IDRETRY    = 4
        IDTRYAGAIN = 10
        IDYES      = 6
    )
    msgboxID := MessageBox("Golang调用dll函数", "系统调用")
    switch msgboxID {
    case IDABORT:
        fmt.Println("用户选择了终止")
    case IDCANCEL:
        fmt.Println("用户选择了取消")
    case IDCONTINUE:
        fmt.Println("用户选择了继续")
    default:
        fmt.Println("用户选择了", msgboxID)
    }
}