Base64 to Binary (Delphi)

Question

I used Binary to Base64 function that you answered : Binary to Base64 (Delphi)

I successfully encode a file to base64 string and write it to MsSQL2008 database, but

Answer 1

This function will take a base64 encoded string, decode it, and write the resulting byte array to a file.

procedure DecodeToFile(const base64: AnsiString; const FileName: string);
var
  stream: TFileStream;
  bytes: TBytes;
begin
  bytes := DecodeBase64(base64);
  stream := TFileStream.Create(FileName, fmCreate);
  try
    if bytes<>nil then
      stream.Write(bytes[0], Length(Bytes));
  finally
    stream.Free;
  end;
end;

To explain what is happening here, the first line

bytes := DecodeBase64(base64);

performs the decode and returns the decoded binary contents of the file in a TBytes variable. TBytes is simply an array of bytes.

The next step is to create the file. The idiomatic way to write files in Delphi is to use streams. In this case we want a TFileStream.

stream := TFileStream.Create(FileName, fmCreate);

The fmCreate option means that if the file already exists, it will be replaced and overwritten by what we write.

The final step is to write the contents of the byte array to the file

if bytes<>nil then
  stream.Write(bytes[0], Length(Bytes));

The if bytes<>nil check is to handle the case where the base64 string decodes to an empty array. If we were to remove that check then the following line would result in a runtime error if you were running with range checking enabled (which you should be doing). The call to stream.Write should be self-explanatory.