Question

How to send struct or pointer using SendMessage or PostMessage function?

Answer 1

Here is simple example:

typedesf struct tagMY_STRUCT{
    unsigned int a;
    unsigned int b;
    unsigned int c;
}MY_STRUCT;

//Some code which sends message
MY_STRUCT *pStruct = new MY_STRUCT;

pStruct->a = 5;
pStruct->b = 4;
pStruct->c = 1;

SendMessage(hWnd, WM_USER + 1, 0, (LPARAM)pStruct);

//WndProc

case (WM_USER + 1) :
{
    MY_STRUCT *pStruct = (MY_STRUCT*)lParam);
    if(pStruct)
    {
        int a = pStruct->a;

        delete pStruct;
    }

}
break;

• Don’t ever try to do it between processes.Study IPC basics first.

• Don’t forget to release pointer to struct once not needed using
  delete.

UPDATE

As Remy Lebeau mentioned in comment, you can also allocate struct on stack instead on heap using new/malloc, because SendMessage block thread until it’s processed in WndProc.This does not apply to PostMessage which add message to window’s message queue and return immediately, so it requires heap block.

However, if you plan to pass more complex data struct I recommend heap allocation instead of stack.