Resource leak in MFC SendMessage()

0
votes

I am new to MFC.

How to release resource which is passed as (WPARAM) in SendMessage().

Here I using "new" to create for it. Following is the snapshot for same.

void Build::BuildCube()
{

    SCtPt *data = new SCtPt;
    data->vm = true;
    int dir = 100;
    MFrame()->SendMessage(WM_MAP_NEW, (WPARAM)data, (LPARAM) dir);
}

I want to make sure "data" resource get released of this function.

Thanks...

3
c++visual-c++mfc
What is MFrame, and how does it handle that message? Does it keep a reference to that pointer around somewhere? Assuming not, you can safely delete once it's finished handling that message, which will be after SendMessage returns. – The Forest And The Trees
Additionally if not, it may be easier for you to either create an automatic variable or use shared_ptr. – The Forest And The Trees

3 Answers

5
votes

Did you consider writing the code like this:

void Build::BuildCube()
{
  SCtPt data;
  data.vm = true;
  int dir = 100;
  MFrame()->SendMessage(WM_MAP_NEW, (WPARAM)&data, (LPARAM)dir);
}

That way the data sent as WPARAM is still a pointer to your object, but when the application gets out of this method's scope, it will invoke the destructor and perform the cleanup for you.

3
votes

As the SendMessage() API is a synchronous API, it sends the message to the other window procedure before returning. When the call to SendMessage() returns, then data can be freed/released:

void Build::BuildCube()
{
    SCtPt *data = new SCtPt;
    data->vm = true;
    int dir = 100;
    MFrame()->SendMessage(WM_MAP_NEW, (WPARAM)data, (LPARAM)dir);
    delete data;
}

Or, better yet, you can avoid allocating the data on the heap altogether. Simply allocate it on the stack and let RAII handle the rest:

void Build::BuildCube()
{
    SCtPt data;       // don't use "new", so you won't get a pointer
    data.vm = true;
    int dir = 100;
    MFrame()->SendMessage(WM_MAP_NEW, (WPARAM)data, (LPARAM)dir);
    // no delete necessary!
}
0
votes

We usually do this :

At the point the data is allocated, the comment state explicitly where it will be deallocated.

void Build::BuildCube()
{

    SCtPt *data = new SCtPt; // Will be deallocated in handler of message WM_MAP_NEW
    data->vm = true;
    int dir = 100;
    MFrame()->SendMessage(WM_MAP_NEW, (WPARAM)data, (LPARAM) dir);
}

LRESULT CMainFrame::OnMapNew(WPARAM wParam, LPARAM )
{
  SCtPt *data = (SCtPt*) wParam;
  // do something with data;

  delete data;
}