TFileStream.ReadAnsiString/WriteAnsiString. Non-printable characters in files

[simone]

I want to read/write some information in a text file using TFileStream.ReadAnsiString/WriteAnsiString.

The drawback I encountered with this methods is that the generated files have the first 4 bytes with the length of every string that is read/written (as in documentation).

This implies that the generated files are not purely textual, having non-printable characters corresponding to the bytes that encode the length of strings.

Is there a way to overcome this inconvenience? Thanks in advance.

[Fibonacci]

If you want to use ReadAnsiString then these 4 bytes are required, otherwise you wouldnt know how long is the string, and there can be multiple strings.

Use other methods, Read/Write or ReadBuffer/WriteBuffer.

[Bart]

I want to read/write some information in a text file using TFileStream.ReadAnsiString/WriteAnsiString.

You're not treating that file as a text file then.
If you want it to be a text file, treat it as a text file.
Either use the TextFile type for the file and use read(ln)/write(ln), use a TStringList and use it's LoadFromFile/SaveToFile methods, or treat it as an untyped file and read into a buffer, parse the buffer, make changes, write the new buffer back to the file.
I personally would not advice the last one though.

Bart

[simone]

Yes, I know how to deal with text files, with the classic approach or with TStringList methods. In my context, I want to use streams because I need to save text files both in files and in memory. Streams, as well known, allow this type of needs to be managed in a unified way.

Since TStream.WriteAnsiString is virtual, while TStream.ReadAnsiString is not (why???), I can't override them to change their behavior. So, using class helpers, I devised this simple solution to manage purely textual (ansi) files with streams:

Code: Pascal  [Select][+][-]

1. program project1;
2. uses
3.   Classes;
4.  
5. type
6.  
7.   { TStreamHelper }
8.  
9.   TStreamHelper=class helper for TStream
10.     function ReadText:string;
11.     procedure WriteText(const Text : string);
12.   end;
13.  
14.  
15. var
16.   FileStream : TFileStream;
17.  
18. { TStreamHelper }
19.  
20. function TStreamHelper.ReadText:string;
21. var
22.   P : PByte;
23. begin
24.   Result:='';
25.   SetLength(Result,Size);
26.   Position:=0;
27.   ReadBuffer(Pointer(Result)^,Size);
28.   P:=Pointer(Result)+Size;
29.   P^:=0;
30. end;
31.  
32. procedure TStreamHelper.WriteText(const Text : string);
33. begin
34.   Position:=0;
35.   WriteBuffer(Pointer(Text)^,Length(Text));
36. end;
37.  
38. begin
39.   //write test
40.   FileStream:=TFileStream.Create('file.txt',fmCreate);
41.   try
42.     FileStream.WriteText('aaabbbccc');
43.   finally
44.     FileStream.Free;
45.   end;
46.  
47.   //read test
48.   FileStream:=TFileStream.Create('file.txt',fmOpenRead);
49.   try
50.     writeln(FileStream.ReadText);
51.   finally
52.     FileStream.Free;
53.   end;
54.  
55.   readln;
56. end.

[KodeZwerg]

I need to save text files both in files and in memory.

Where do you think goes the data of a loaded TStringList when not in memory?
And for your code I suggest to use AnsiString/PAnsiChar type to be future compatible and to inform users of your code, what it really is compatible with.

[jamie]

There is:

  TStringStream

With that, it builds a single data-String from any strings you write to it and there is no BIN header information stored.

At any point, you can use a TfileStream and load or copy this stream elsewhere, etc.

[simone]

Where do you think goes the data of a loaded TStringList when not in memory?

The fact that a TStringList goes into memory has no relevance to my initial post. My context is that of a diagram editor. I use TFileStream to load/save diagrams from/to files and TMemoryStream to save states for the purpose of implementing undo/redo functions.

And for your code I suggest to use AnsiString/PAnsiChar type to be future compatible and to inform users of your code, what it really is compatible with.

Fair observation. I agree.

There is:

  TStringStream

With that, it builds a single data-String from any strings you write to it and there is no BIN header information stored.

At any point, you can use a TfileStream and load or copy this stream elsewhere, etc.

This is a good alternative to the approach I used.

[Bart]

In my context, I want to use streams because I need to save text files both in files and in memory. Streams, as well known, allow this type of needs to be managed in a unified way.

TStringList does have SaveToStream/LoadFromStream...

Bart

[simone]

You are right. What you propose is probably the simplest solution to the problem I described.