How to Access Serial Ports Greater Than COM9 Using C/C++

The following is a tech note published by Microsoft, regarding a solution to accessing com ports above Com 9.
 
HOWTO: Specify Serial Ports Larger than COM9Last reviewed: January 20, 1997Article ID: Q115831
The information in this article applies to:

Microsoft Win32 Application Programming Interface (API) included with:

    - Microsoft Windows NT versions 3.1, 3.5, 3.51, 4.0
    - Microsoft Windows 95 version 4.0

CreateFile() can be used to get a handle to a serial port. 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. CreateFile() is successful when you use "COM1"through "COM9"for the name of the file; however, the message "INVALID_HANDLE_VALUE"is returned if you use "COM10"or greater. If the name of the port is//./COM10, the correct way to specify the serial port in a call to CreateFile() is as follows:

   CreateFile(
      "////.//COM10",     // address of name of the communications device
      fdwAccess,          // access (read-write) mode
      0,                  // share mode
      NULL,               // address of security descriptor
      OPEN_EXISTING,      // how to create
      0,                  // file attributes
      NULL                // handle of file with attributes to copy
   );

NOTES: This syntax also works for ports COM1 through COM9. Certain boards will let you choose the port names yourself. This syntax works for those names as well.
Additional reference words: 3.10 3.50 4.00 95KBCategory: kbprg kbhowtoKBSubcategory: BseCommapi