MFC, C++: Creating a user-defined message that calls a function with several parametres

Posted on 2007-11-26
Last Modified: 2013-12-14

It has become necessary to send a user defined message. I intend to do this using SendMessage().

I can obtain a handle to the CWnd I want to send the message to.

In essence, I want to call an identical function from any one of various classes by sending a message to the object.

I can see from that SendMessage() has three parametres, but the function I wish to call has several parametres.

This is one of the class functions (the other ones are identical anyway):

void CSearch::OnChangedRowUpdate(CString description, CString dept, CString source, CString supplier, CString cos)
      int i = ProductReport.GetFirstSelectedItem();


How should I go about defining a WM_APP message that will call this (or an identical) function, and how should I send that message so that it will call the function with specified parametres?

Question by:sternocera
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Accepted Solution

jkr earned 500 total points
ID: 20351308
User-defined handlers are declared as

// example for ON_MESSAGE
#define WM_MYMESSAGE (WM_USER + 1)
BEGIN_MESSAGE_MAP( CMyWnd, CMyParentWndClass )
    //{{AFX_MSG_MAP( CMyWnd
    // ... Possibly more entries to handle additional messages

or in your case

#define WM_ROWUPDATE (WM_USER + 1)
BEGIN_MESSAGE_MAP( CMyWnd, CMyParentWndClass )
    //{{AFX_MSG_MAP( CMyWnd
    ON_MESSAGE( WM_ROWUPDATE , OnChangedRowUpdate)
    // ... Possibly more entries to handle additional messages

However, the problem still remains that there are only two parameters. You could however wrap up yours in a struct and pass a pointer to that as LPARAM, e.g.

struct RowUpdateData
 CString description;
 CString dept;
 CString source;
 CString supplier;
 CString cos;

LRESULT CSearch::OnChangedRowUpdate(WPARAM, LPARAM lParam)
      RowUpdateData* p = (RowUpdateData*) lParam
      int i = ProductReport.GetFirstSelectedItem();


Author Comment

ID: 20356504
I'm attempting to call SendMessage:

SendMessage(pParentWindow->m_hWnd,WM_ROWUPDATE, 0, &Mystruct);

Visual studio complains:

error C2660: 'CWnd::SendMessageA' : function does not take 4 arguments

According to , the function does take 4 arguments. I need to be able to send it to my CDialog's parent window (which varies), a handle to which is obtained by:

CWnd* pParentWindow = GetParent();


Author Comment

ID: 20356582
oh, I see.

It was simply a matter of calling ::SendMessage


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