Createfile com port All throughout the article we are going to use a file handle as serial port agent. The following example opens a handle to COM2 and fills in a DCB structure with the current configuration. It continues to return 0xfffff (the Invalid_Handle_Value). By setting the dwCreationDisposition parameter to OPEN_EXISTING, read-only, write-only, or read/write access can be specified. The May 17, 2011 · Stack Overflow for Teams Where developers & technologists share private knowledge with coworkers; Advertising & Talent Reach devs & technologists worldwide about your product, service or employer brand Mar 12, 2025 · 进程使用 CreateFile 函数打开通信资源的句柄。 例如，指定 COM1 将打开串行端口的句柄，LPT1 将打开并行端口的句柄。 如果指定的资源当前正由另一个进程使用，CreateFile 将失败。 进程的任何线程都可以使用 CreateFile 返回的句柄来标识访问资源的任何函数中的资源。 Jul 3, 2024 · It all works fine except that on some devices there can be a ~5 second delay before CreateFile() fails with INVALID_HANDLE_VALUE because the COM port is already being accessed --- the failure is correct, but what I'm trying to do is reduce the 5 second wait to as little as possible, otherwise our program seems to just stall from the customer's Jan 6, 2021 · In this article. Using the C code outlined below (extract from a larger program) in Visual Studio 2110 express, I am having difficulty using CreateFile to return a valid pointer. On success CreateFile() returns a handle that can be used to access the file or device depending on the flags and attributes specified. So if you want to make the port a variable say comPort to be used as such: CreateFile(comPort,. Apr 18, 2005 · Hello All, I am trying to read data from a serial port in C using Win32 API. Oct 20, 2002 · The purpose of this is to create the serial port agent. Alfred, you're missing an underscore in that symbol. The getLastError code, 2, tells me the file does not exist. Consoles The CreateFile function can create a handle to console input (CONIN$). The function that is used to create the serial port handle is the CreateFile function. \" must be added to the com port string, for example "\\. \\ is a format and will result in CreateFile actually seeing \\. May 18, 2014 · 今天用以前的一个串口程序，发现串口怎么也打不开。因为用的串口不是常规的COM1、COM2而是大于Com10的端口，想着是很简单的增加几个选项就可以轻松搞定的，结果加上后测试，发现总是初始化失败，调试发现在CreateFile里总是失败，找到MSDN一看果然这里有区别。 ポートを開く. \ as a prefix for COM port greater than 9. ① CreateFile()関数で ファイルをオープンする。（COMポートのハンドルを取得する） ② SetupComm() PurgeComm()関数で送受信バッファーの設定及び初期化をおこなう Feb 8, 2023 · The CreateFile function can create a handle to a communications resource, such as the serial port COM1. For more information about communications, see Communications. Everything is working fine till opening the port and now I tried to read the data from COM port using ReadFile() in overlapped mode. For COM numbers less than 9 CreateFile is called with a string such as: "COM1". Feb 8, 2023 · The CreateFile function can create a handle to a communications resource, such as the serial port COM1. 通信設定 BOOL GetCommState( HANDLE hFile, // 通信デバイスのハンドル LPDCB lpDCB // DCB（デバイス制御ブロック）構造体へのポインタ); Jan 6, 2021 · For example, specifying COM1 opens a handle to a serial port, and LPT1 opens a handle to a parallel port. Sep 14, 2012 · The CreateFile function can create a handle to a COM port. I created a thread from the main program which is an NT service and opened the port. The CreateFile() is a Win32 API that creates or opens a file or I/O device. You . In Windows using the CreateFile(), we can open the serial port. For communications resources, the dwCreationDisposition parameter must be OPEN_EXISTING , the dwShareMode parameter must be zero (exclusive access), and the hTemplateFile parameter must be NULL . Volume handles may be opened as noncached at the discretion of the file system, even when the noncached option is not specified with CreateFile. CreateFile() を使用すると、シリアル ポートのハンドルを得ることができます。 この場合、共有モード パラメータには 0 、クリエイト パラメータには OPEN_EXISTING 、テンプレート パラメータには NULL を設定しなければいけません。 To specify a COM port number greater than 9, use the following syntax: "\. Creating a port handle. The CreateFile function can create a handle to a communications resource, such as the serial port COM1. \COM23. . \\COM%d Where %d is a printf-substitution for the port number. The serial port's handle is a handle that can be used to access the object of serial port. \COM24". Why is this so? In Windows using the CreateFile(), we can open the serial port. If the specified resource is currently being used by another process, CreateFile fails. \COM10". Nov 17, 2014 · HANDLE CreateFile( LPCTSTR lpFileName, // file name DWORD dwDesiredAccess, // access mode DWORD dwShareMode, // share mode LPSECURITY_ATTRIBUTES lpSecurityAttributes, // SD Oct 12, 2023 · 最初の行で HANDLE 型変数を作成し、関数 CreateFile を呼び出してそれを初期化しました。 この関数の最初の引数は、開く必要があるファイルの名前です。 @Ferruccio: A serial port named COM10 does not necessarily mean the computer actually has 10 ports. The "Win32 Programmer's Reference" entry for "CreateFile()" mentions that the share mode must be 0, the create parameter must be OPEN_EXISTING, and the template must be NULL. The DCB structure is then modified and used to reconfigure the device. If the process has an Jul 22, 2011 · Remember that \\\\. For communications resources, the dwCreationDisposition parameter must be OPEN_EXISTING, the dwShareMode parameter must be zero (exclusive access), and the hTemplateFile parameter must be NULL. ); then the variable needs to print out looking like \\. _T("COM1") Under UNICODE builds, _T("") maps to L"", which is what TEXT("") maps to, which is why that works for you; and under MBCS/ANSI builds, _T("") maps to "" which is why your original doesn't work for you because windows functions are mapped to A/W versions that accept either Ansi or Unicode strings depending on whether Apr 8, 2011 · 打开COM1到COM9用：m_hCom = CreateFile(_T("COM1:"), GENERIC_READ | GENERIC_WRITE, 0, NULL, OPEN_EXISTING, NULL, NULL);或者m_hCom = CreateFile(_T(&qu USB com ports are typically assigned port numbers greater than 9, which impacts how the CreateFile function must be called. You Jul 22, 2011 · I'm using the CreateFile function to create a handle to the COM port. Any thread of the process can use the handle returned by CreateFile to identify the resource in any of the functions that access the resource. Sep 30, 2014 · hCom = CreateFile( "COM1", GENERIC_READ | GENERIC_WRITE, 0, NULL, OPEN_EXISTING, 0, NULL ); I have just one COM port on my computer, but this function returns for COM1, COM3, COM4, COM5, COM6, COM7 a value unless "INVALID_HANDLE_VALUE". Jun 26, 2024 · 不能使用 CreateFile 来控制文件或目录上的压缩、解压缩或解密。 有关详细信息，请参阅 创建和打开文件、文件压缩和解压缩，以及 文件加密。 Windows Server 2003 和 Windows XP：出于向后兼容性目的，CreateFile 在 lpSecurityAttributes中指定安全描述符时，不会应用继承规则 概要. However, it always returns INVALID_HANDLE_VALUE. CreateFile()で開きます。. You need to use the following format for COM ports greater than 9: \\\\. The "\" denotes termination in C. I can configure what number is assigned to what COM port, so it's possible to have only 3 serial ports attached but have them named COM12, COM5, and COM37 for example. This syntax works for all port numbers and hardware that allows COM port numbers to be specified. For numbers greater than 9, a prefix of "\\. Devices. CreateFile() can be used to get a handle to a serial port. Dec 3, 2012 · +1 Michael. Why? Well, this accesses the global NT object space, where all objects are stored. vdasl mtl hxnit oxjnpk vmjitc ylf ghjkurx avrhw baa mesg jpqn ynvwm lbwfsfg zuazot axztbzu