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Asked: 2026-06-07T08:21:48+00:00

In C++ WinAPI application I open the file using this code CreateFileW(path,FILE_APPEND_DATA,FILE_SHARE_READ,NULL,OPEN_ALWAYS,FILE_ATTRIBUTE_NORMAL,NULL); While the

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In C++ WinAPI application I open the file using this code

CreateFileW(path,FILE_APPEND_DATA,FILE_SHARE_READ,NULL,OPEN_ALWAYS,FILE_ATTRIBUTE_NORMAL,NULL);

While the file is opened by this C++ app, I’m trying to open it for reading in C# app, using this code

var f = new StreamReader(path);

I get IOException “The process cannot access the file because it is being used by another process”

I tried 

var fs = new FileStream(path, FileMode.Open,FileAccess.Read)

Same result.

I can’t understand why this is happening. I specified FILE_SHARE_READ in CreateFile in my C++ app. I open it for reading in C#. It must open in C# app. What am I doing wrong?
At the same time, notepad.exe can open this file

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1 Answer

  1. Editorial Team

    The FileStream constructor you’re using in the C# app opens the file with the FileShare.Read option, equivalent to FILE_SHARE_READ.

    This means that other programs are allowed to have the file open for reading, but not for writing, while you have the file open. But your C++ program already has the file open for writing, so the sharing mode you’ve requested isn’t possible and the attempt to open the file fails.

    Instead, say this:

    var fs = 
  new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.ReadWrite)
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