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Editorial Team
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Asked: 2026-05-27T15:28:51+00:00

I am saving some Objects I have defined from my own classes, to File.

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I am saving some Objects I have defined from my own classes, to File. (saving the stream data).

That is all fine, but I would like to be able to store in the File the CRC checksum of that File.

Then, whenever my Application attemps to Open a File, it can read the internally stored CRC value.

Then perform a check on the actual File, if the CRC of the File matches the internally stored CRC value I can process the File normally, otherwise display an error message to say the File is not valid.

I need some advice on how to do this though, I thought I could do something like this:

  • Save the File from my Application.
  • Calculate the CRC of the Saved File.
  • Edit the Saved File storing the CRC Value.
  • Whenever a File is Opened, Check the CRC matches internal CRC Value.

Problem is, as soon as a single Byte of Data is altered in the File, results in the CRC checksum being completely different – as expected.

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1 Answer

  1. Editorial Team

    Simply put you need to exclude the bytes used to store the checksum from the checksum calculation.

    Write the checksum as the last thing in the file. Calculate it based on the contents of the file apart from the checksum. When you come to read the file calculate the checksum based on the contents before the checksum. Or you could write the checksum as the first bytes of the file with random access. Just so long as you know where it is.

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