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Question I could use my Application Program to open COM1~COM9. But why couldn't I open ports numbered 10 or higher, such as 'COM10', 'COM11', etc., when using WIN32 SDK to develop a program in Borland C++ Builder/ Visual C++ to control ports?
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Updated 4/1/2008 5:07:20 PM
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The main reason is that Win32 API's device naming convention for COM ports uses the form "\\.\COMx". For example, if the device name of COM10 is "\\.\COM10", then COM11 will be "\\.\COM11".

Under the Visual C++ environment:

You need to use the format "\\\\.\\COMx" as the COM port device name when using Win32 API to develop your program.

For example, the device name of COM10 is "\\\\.\\COM10"

Under the Borland C++ Builder:

You need to use the format "\\.\COMx" as the COM port device name when using Win32 API to develop your program.

For example, the device name of COM10 is "\\.\COM10"

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