How to read open excel file at C#

I want to read already open excel file with C#. I am using this method but it can't read the excel file while the file is open in Microsoft excel.

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FileStream stream = File.Open("myfile.xlsx", FileMode.Open, FileAccess.Read);

It gives IOException: The process cannot access the file 'myfile.xlsx' because it is being used by another process.

I hope you understands what I mean. I want to keep excel file open and while file is open at Microsoft excel i want to read it from C#. I am using C# net framework 4.0

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You need to open it with FileShare.ReadWrite:

FileStream stream = File.Open("myfile.xlsx", FileMode.Open, FileAccess.Read, FileShare.ReadWrite);

See this answer.

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I think you can still copy the file while excel has it open, so you could make a copy of the file and then open that. Just make sure you clean up after yourself when you are done with the copy.

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You could use the Interop library to use the already opened instance of Excel.

oExcel == (Excel.Application) System.Runtime.InteropServices.Marshal.GetActiveObject("Excel.Application")

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You can try the File.Open with a fourth parameter - fileShare.

FileStream stream = File.Open("myfile.xlsx", FileMode.Open, FileAccess.Read, FileShare.Read);

You may need to specify write access also.

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To ensure that correct opening and closing of the file please look at using the c# using statements

using (FileStream stream = File.Open("myfile.xlsx", FileMode.Open, FileAccess.Read)) 
{

}

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To open the same file more than once at the same time, it needs to be opened in shared mode.

Hope this may help others.