Hi All,

I'm studying how pascal manages strings. I wrote a simple test program:

program stringtest;
{$mode objfpc}{$H+}
uses Classes, sysutils;
function test: PString;
var
  s : string;
begin
  New(Result);
  Result^ := FloatToStr(Random);
//  s := FloatToStr(Random);
//  Result := @s;
end;
var
  i : Integer;
begin
  Randomize;
  with TList.Create do try
    for i := 0 to 9 do Add(test);
    for i := 0 to Count - 1 do begin
      WriteLn(PString(Items[i])^);
    end;
  finally
    Free;
  end;
end.

The program runs fine, but:

1. I don't know whether I have to MANUALLY free memory for these strings to prevent leak?
2. Does the IDE provide any facility to analyze memory usage of a program and report if there are any leaks? (There are Tools/Leak View, but I don't know how to get .trc file, or is it what I thought.

Thanks.

I think this can answer a few questions:
http://www.freepascal.org/docs-html/ref/refsu12.html#x35-380003.2.6

AFAICS your code will leak both the String contents and the PString pointer. You have to store the result from test() and call Finalize or assign '' to it (actually its "dereference").

var i : Integer;

     p: PString;

begin

...

for i := 0 to Count - 1 do begin WriteLn(PString(Items[i])^);

         p := PString(Items[i]);
         p^ := ''; // or Finalize(p^);
         Dispose(p);

end;

Best regards,
Flávio

Yes, if you work like this, you must do all that.
You must free all pointers in the list, and the strings they point to.

But why not use TStringList ? It does all this for you.

> 2. Does the IDE provide any facility to analyze memory usage of a program > and report if there are any leaks? (There are Tools/Leak View, but I don't > know how to get .trc file, or is it what I thought.

You can use the -gh compiler command-line option, then you'll get a listing of memory leaks.

Michael.

The string types "String" (in mode $H+), "AnsiString" and "UnicodeString" are managed by the compiler/RTL. If you use a pointer type then you need to manage it yourself, thus you need to free the PString manually in this case.

Regards,
Sven

2013/4/19 Michael Van Canneyt

Because I want to then concat the strings into a big string using CRLF, but the TStringList.Text method concat them using LF only. I think that might be platform dependant, which is not what I want.

Now I use a TStringStream for this purpose.

It seems that TextLineBreakStyle is what you want: http://www.freepascal.org/docs-html/rtl/classes/tstrings.textlinebreakstyle.html

Regards,
Sven