String in Windows message

Posted on 2010-11-17
Last Modified: 2012-06-21
Hello experts

I know how to send message to the system.
It looks like:

PostMessage(MyParams.HandleToForm, WM_THREAD_COMPLETE, LInteger0,

Where I have handle to the form with procedure, name of the procedure and two integer parameters.


How can I pass parameter of String type?

Thank you

Question by:panJames
  • 4
LVL 19

Expert Comment

ID: 34154219
LVL 24

Expert Comment

ID: 34154231
You can do something like this:

Str : String;

PostMessage(MyParams.HandleToForm, WM_THREAD_COMPLETE, @Str, LInteger1);
LVL 24

Expert Comment

ID: 34154285
That one will not work. But this will:

  A : Integer;

  Str := 'test';
  A := GlobalAddAtom(Pchar(Str));
  PostMessage(MyParams.HandleToForm, WM_THREAD_COMPLETE, iAtom, LInteger1);
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LVL 24

Expert Comment

ID: 34154403
  A : Integer;

  Str := 'test';
  A := GlobalAddAtom(Pchar(Str));
  PostMessage(MyParams.HandleToForm, WM_THREAD_COMPLETE, A, length(Str));
LVL 24

Accepted Solution

jimyX earned 500 total points
ID: 34154615
This also is valid:

Str : String;

PostMessage(MyParams.HandleToForm, WM_THREAD_COMPLETE, integer(Str), length(Str));
LVL 26

Expert Comment

by:Russell Libby
ID: 34155054
Just keep the following rules in mind when passing strings (or any pointers, eg objects, etc):

- If you PostMessage with a string, you have to ensure the pointer (string) does not go out of scope before the window processes the message. Not a recommended way of sending strings.
- If you are SendMessage(..) ing strings/pointers, you can do so without issues as long as the window handling the message exists within the process.
- If you are SendMessage(..) ing strings/pointers to a window that exists in another process, then you will need to use some form of IPC (WM_COPYDATA, atoms, etc) as the pointer you are passing needs to be mapped into the process space of the window handling the message.



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