Calculating CRC32 File Hash in Delphi

In software development, ensuring data integrity and verifying whether a file has changed is a common requirement. One effective way to achieve this is by using the CRC32 (Cyclic Redundancy Check) hash, which is a popular method for detecting changes in files. In this blog post, we will explore a Delphi function that calculates the CRC32 hash of a file, allowing you to detect any modifications easily.

Let's dive into the function:

function PACalculateCRC32FromFile(const FileName: string): string;

// Calculate FAST CRC32 File Hash (e.g. for the purpose of detecting if a file has changed)

var

  IdCRC32: IdHashCRC.TIdHashCRC32;        // Declare a variable to hold the CRC32 hash object

  FileStream: System.Classes.TFileStream; // Declare a variable to hold the file stream

  CRC32: Cardinal;                        // Declare a variable to hold the CRC32 value

begin

  IdCRC32 := TIdHashCRC32.Create;   // Create an instance of the CRC32 hash object

  try

    // The file specified by FileName is opened in read-only mode with shared deny-write access.

    // This ensures that the file can be read while preventing other processes from writing to it:

    FileStream := TFileStream.Create(FileName, fmOpenRead or fmShareDenyWrite); // Open the file for reading

    try

      CRC32 := IdCRC32.HashValue(FileStream); // Calculate the CRC32 value of the file

      // The computed CRC32 value, which is a Cardinal type, is converted to an 8-character hexadecimal string.

      // This makes the result more readable and suitable for comparison purposes:

      Result := IntToHex(CRC32, 8);           // Convert the CRC32 value to a hexadecimal string

    finally

      FileStream.Free;  // Ensure the file stream is freed even if an exception occurs

    end;

  finally

    IdCRC32.Free;  // Ensure the CRC32 hash object is freed even if an exception occurs

  end;

end;