Trouble converting PChar to String

[DavidTh30]

procedure TForm1.Button2Click(Sender: TObject);
var
  i:integer;
begin
  for i:=0 to 1000 do
  ShowMessage(PChar(PByte(i)));
end;

How can I filter this PChar is 'string' or 'not string'.
"Try Except Finally" does not work for this kind of SIGSEGV error.

[Mr.Madguy]

What do you try to do? Read memory from address 0 to 1000? Not sure about Win64, but on Win32 this memory isn't readable. First 64k of memory is reserved for handles. I.e. address < 64k is handle and address >64k is address.

P.S. If you need to convert integer to string - use IntToStr. If you need to print contents of  integer as string - use PChar(@i).

[DavidTh30]

Normally during transfer DDE "Dynamic data exchange" using option "CF_TEXT", Microsoft always use variable "PByte".
Sometimes I got wrong pointer signal, So I receive something not a string.
Same thing in this case I got SIGSEGV error "cmpb".

I already try to convert using function copy PChar, I got SIGSEGV error "mov".

I'm not sure that hDataQUOTE address < 64k or >64k.

[jamie]

A miss use of pointers.

Code: Pascal  [Select][+][-]

1. Achar := pchar(astring)^[someindex];
2.  

On those lines.

[DavidTh30]

Maybe I miss use of pointers.

// Pointers example#1
procedure TForm1.Button1Click(Sender: TObject);
var
  Pch1:^Char;
  Pch2:PChar;
  i:integer;
  i2:double;
  Pb:PByte;
  Pr:^real;
begin
  for i:=0 to 20 do
  begin
    i2:=i*0.123;  Pr:=@i2;
    Pb:=@i;  Pch1:=PChar(Pb); Pch2:=@i;
    ShowMessage(Pch1+' '+Pch2+ ' ' + IntToStr(Pb^)+ ' ' + FloatToStr(Pr^));
  end;
end; 

 

[jamie]

Why dont u tell us exactly what u are trying for?

[Handoko]

He was trying to convert PChar to String.

[jamie]

U need know if ms is using widechar strings in the dde transaction.

[jamie]

Looking at your field variable names that start with an 'h' tells me that maybe a handle to an object not a direct pointer to use.

 I would try using a globallock( the handle ) which will return the pointer.

Also dont forget to unlock it.

[DavidTh30]

SIGSEGV error Interrupt on top of "Try Except Finally".
How can I know that target address is string, integer or double?

[winni]

SIGSEGV error Interrupt on top of "Try Except Finally".
How can I know that target address is string, integer or double?

Hi!

If you don't know the logical use of that address you'll never know.

You can read an array of byte and then you can check if there are errors if you convert it to a float.
Or if the converting to a string makes some sense.

So again ( and again and again) like Mr. Madguy said:

What are you trying to do??????

Winni

[ASBzone]

SIGSEGV error Interrupt on top of "Try Except Finally".
How can I know that target address is string, integer or double?

At some point, I suspect that people are going to stop trying to help you until you answer the very basic question of "what are you trying to accomplish?"

Not at the task level, but at the project level.  What are you looking to accomplish overall with this application?

Without that, it is going to be very hard to help you solve your issue.   

[jamie]

looking here

https://forum.lazarus.freepascal.org/index.php?topic=39403.0


I would say you have been working on this for a while now..

I don't see you using "DdeCreateStringHandle" for the  P_.HSZPair

Field.

 A handle is needed from the Dde system so it knows how to manage the string ,.

[Handoko]

procedure TForm1.Button2Click(Sender: TObject);
var
  i:integer;
begin
  for i:=0 to 1000 do
  ShowMessage(PChar(PByte(i)));
end;

That is wrong. These below are correct:

Code: Pascal  [Select][+][-]

1. procedure TForm1.Button1Click(Sender: TObject);
2. var
3.   aByte:  Byte;
4.   aPByte: PByte;
5.   S:      string;
6.   i:      Integer;
7. begin
8.   S      := '';
9.   aPByte := @aByte;
10.   for i := 1 to 20 do begin
11.     aByte := i;
12.     S     := S + (aPByte^).ToString + ' ';
13.   end;
14.   ShowMessage(S);
15. end;

Code: Pascal  [Select][+][-]

1. procedure TForm1.Button1Click(Sender: TObject);
2. var
3.   aPChar: PChar;
4.   S:      string;
5.   i:      Integer;
6. begin
7.   S := 'Hello';
8.   for i := 0 to S.Length - 1 do begin
9.     aPChar := @S[1];
10.     Inc(aPChar, i);
11.     ShowMessage(aPChar^);
12.   end;
13. end;

[lucamar]

Shouldn't the second be:

... some code deleted ...[/]

Otherwise, it will end up pointing always to S[2].

Just saying

Never mind me ... didn't really look: Inc(aPChar, i);