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Asked: 2026-06-15T19:20:37+00:00

I need to pass a pointer to an std::string as the LPARAM of a

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I need to pass a pointer to an std::string as the LPARAM of a WM_USER message and get the string or char* in the WM_USER message handler of the main window.

How do I do that ?

What I am doing now (which is incorrect, since its not producing the result it should):

PostMessage(hwnd, LP_DOWNLOADUPDATE, (WPARAM)hHandleToWindow, (LPARAM)&remSize);

Where remSize is a sdt::string remSize; a global variable.

And in the message handler I am doing :

SetWindowText( (HWND)wParam, (char*)lParam );
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1 Answer

  1. Editorial Team

    Just must get a C-style string, i.e. a pointer to a zero-terminated array of characters:

    PostMessage( hwnd, LP_DOWNLOADUPDATE, (WPARAM)hHandleToWindow, remSize.c_str() );

    Make sure remSize doesn’t go out of scope until you can be sure that the message has been processed, or else there will be dangling pointer.

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