How to allow a file to be read but not written to when my app is using the file?

Question

How to allow a file to be read but not written to when my app is using the file?

Cynolycus 285

I have two text files that store information that my Windows Forms App uses.

I usually open the files in Excel to view the changes my app is making to them but if I leave it open and start my app the app generates an error because the file is open.

I now have code in place that stops the app from starting if the files are in use but if the file is opened while the app is running, the app doesn't like it and crashes.

I am thinking that when my app starts it needs to prevent the files from being opened by another process while my app is running.

With other programs like Word you could open a file that was already in use by another process but it would be opened in readonly mode.

Is there a way that I can get my app to allow the files to be read but not written to?

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Answer 1

Jiachen Li-MSFT 34,241 Microsoft External Staff

Hi @Cynolycus ,

Please try set the FileShare.Read when you open the file.

If your application allows users to make data modifications, be sure to save changes regularly and release access to the file promptly so that other applications can open the file read-only after it is released.

Best Regards.

Jiachen Li

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Cynolycus 285 Reputation points

2023-12-19T02:52:45.92+00:00

Thank you Jiachen Li ,

My App only reads or writes to the files for a very short time using StreamReader and StreamWriter, but does it when changes are made that need to be saved, then the file is read back to the App to ensure that the information in the App is current.

The rest of the time it isn't using the files which is when other processes can access it and if they have it open when my App needs to save, then the App crashes.

I believe that what you are saying is that my App take control of the files when it starts, preventing access, but during the time my App is not using the files then I should use FileShare.Read to allow other processes to read the files.

When my App needs to save the files then remove the FileShare.Read so no process can use the files.

When my App is closed then it releases the files completely.

Would I have to use FileStream instead of StreamReader and StreamWriter to read and write to the files to be able to use FileShare.Read?
Jiachen Li-MSFT 34,241 Reputation points Microsoft External Staff

2023-12-19T09:46:38.7866667+00:00

Hi @Cynolycus ,

It also depends on the other app you're using, and if it locks the file when it opens it, your own app will of course get an error when it modifies the file.
Jiachen Li-MSFT 34,241 Reputation points Microsoft External Staff

2023-12-28T12:50:45.3333333+00:00

May I know if you have got any chance to check my answer? I am glad to help if you have any other questions.

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How to allow a file to be read but not written to when my app is using the file?

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