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Mark Salsbery
Microsoft MVP - Visual C++
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I have a DLL that has a class derived from CWinApp.
I have another class in the DLL that needs to trigger an asynchronous process within that same DLL. Since the DLL has no window I use PostThreadMessage to trigger the process as follows:
<code>void CMyClass::TriggerAsyncProc() const
{
AfxGetApp()->PostThreadMessage(WMU_MYMSG, 0, 0L) ;
}</code>
In my class derived from CWinApp, I have tried two different methods to trap WMU_MYMSG. The first was to override PreTranslateMessage, and the second was to try to use the CWinApp message map (via ON_THREAD_MESSAGE).
The DLL is being used by a dialog application, and the TriggerAsyncProc is definately sending the message because PostThreadMessage(WMU_MYMSG, 0, 0L) returns non-zero.
The only thing I can think of is that my message is going through the message map of the dialog application instead of my class derived from CWinApp in the DLL.
Please can someone tell me why I'm losing the message, and suggest either how I correct this or an alternative method?
Thanks.
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This doesn't sound like it would work.
A DLL that has a CWinApp object is supported, but that CWinApp object doesn't have its own message pump.
I wouldn't expect any messages to be processed in the DLL's CWinApp object unless you've tweaked something
to do so.
Here's what the docs state about this situation:
"Note that the CWinApp::Run mechanism does not apply to a DLL, because the application owns the main message pump.
If your DLL brings up modeless dialogs or has a main frame window of its own, your application's main message pump must
call a DLL-exported routine that calls CWinApp::PreTranslateMessage."
Mark
Mark Salsbery
Microsoft MVP - Visual C++
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Thanks for that. It's a pity that the DLL Wizard created a CWinApp derived class that includes Message Map macro declarations.
There is a possiblity that the main applications using my DLL will not have a main frame window - they may also be ATL applications. Please could you advise what I could do in these cases?
Thanks
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I would suggest reading this: Kinds of DLLs[^]
It outlines the methods and requirements of different MFC DLL scenarios.
Maybe it'll help choose an appropriate method for your needs.
Mark
Mark Salsbery
Microsoft MVP - Visual C++
![Java | [Coffee]](https://www.codeproject.com/script/Forums/Images/coffee.gif)
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Thanks again.
Not a lot of help there about this particular situation, but some useful info. none the less.
Cheers.
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What I have done within a DLL 'init' function that the client must call - AFTER the client has already loaded all its dll and such, is to create a new thread. All the work within the DLL I wrote was done from within this thread internal to the DLL.
At the top of this thread place a PeekMessage call, so the thread will get a message queue. Then you can process 'posted thread messages' fromt this thread and it has its own independent message pump.
Just because an app stared as a dialog app, or some other type of app, does not mean it can't have a DLL containing its own thread and its own message queue.
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Yeah. The main point is...
when using MFC in a "regular DLL" (that can be used by an MFC or non-MFC app) then
you have to provide the message pump.
There's also subtle differences in MFC initialization, but if you use the wizards, that code
is created for you.
Mark
Mark Salsbery
Microsoft MVP - Visual C++
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Hi,
Suppose I have a method foo that takes a const char* param. I have a case where I can be more efficient if the caller passes in a "quoted literal string" vs the contents of some arbitrary buffer (because I don't have to copy the string data in the first case).
((UPDATE: To be clear, the class with method foo needs to store the supplied string away for later access, internally. For a literal string, it's safe to store the pointer only. For a non-literal, it's necessary to copy the data in case the original caller's buffer goes away or is modified before the class instance goes away.))
Pretty sure the answer is "you can't", but I thought I'd check if anyone can think of a way to overload the method foo such that one version is invoked for
char buff[100];<br />
...<br />
const char* p_buff = buff;<br />
myclass.foo(p_buff)
and the second version is invoked for
myclass.foo("literal string")
?
I can't change the name of foo or have the caller specify explicitly which one they want. This sample is just an illustration.
Thanks!
DB
-- modified at 12:11 Friday 3rd August, 2007
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dburns wrote: Hi,
Suppose I have a method foo that takes a const char* param. I have a case where I can be more efficient if the caller passes in a "quoted literal string" vs the contents of some arbitrary buffer (because I don't have to copy the string data in the first case).
IMHO, You completely miss the efficience target...
i.e. don't bother about.
If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler.
-- Alfonso the Wise, 13th Century King of Castile.
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CPallini wrote: IMHO, You completely miss the efficience target...
Actually we've done profiling on this code and it really does matter.
You may be picturing one or two invocations but picture 10s of millions
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But you don't need to copy anything,
simply cast the pointer!
If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler.
-- Alfonso the Wise, 13th Century King of Castile.
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We really DO need to copy the data because the C++ object that I called "myclass" may outlive the buffer that contained the original data. If we just stored the supplied pointer, then it would be pointing to a buffer on the stack, which would be wiped out when the function returned. Then the "myclass" object would have a pointer to garbage.
If the pointer is truly a "literal string" then that's not an issue. That's why I'm trying to detect that case to be more efficient.
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But (in the OP) you're not copying data, you're just copying the address. ...is there a mistake in the air?
MODIFIED:
Or are you're talking about an internal copy done by you're class?
in that case you've simply to differentiate calls to foo() member, for instance:
foo(const char * pBuffer)
{
...
foo_without_copy(pCopiedBuffer);
}
foo_without_copy( const char * pBuffer)
{
...
}
If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler.
-- Alfonso the Wise, 13th Century King of Castile.
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CPallini wrote: Or are you're talking about an internal copy done by you're class?
Yes, that's exactly right. Perhaps you've illustrated it better than I did in the original post.
However, I can't use foo and foo_without_copy. In the OP I indicated that I can't have the caller make the explicit choice. I need the compiler to differentiate, if it's possible. I doubt it is.
Maybe I'm just lazy but we're talking a million lines of code here and I'd rather the compiler did the work rather than me searching and changing each one
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dburns wrote: I need the compiler to differentiate, if it's possible. I doubt it is.
It makes me wonder if the two addresses would be in different areas. String literals would be in the stack area, whereas dynamically-allocated memory would be in the heap. Hmmm...
"A good athlete is the result of a good and worthy opponent." - David Crow
"To have a respect for ourselves guides our morals; to have deference for others governs our manners." - Laurence Sterne
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Now that's outside-the-box thinking!! I think I'm a little chicken to go that route though...
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He states this is a performance issue. Analyzing memory addresses at runtime would defeat the purpose yes?
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They're just numbers, so I wouldn't think the impact would be that substantial. Without empirical data, however, I wouldn't know for sure.
"A good athlete is the result of a good and worthy opponent." - David Crow
"To have a respect for ourselves guides our morals; to have deference for others governs our manners." - Laurence Sterne
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dburns wrote: I'd rather the compiler did the work
This is a design issue. Compilers are NOT intended to "design" or make up for a poor design.
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dburns wrote: ..."quoted literal string" vs the contents of some arbitrary buffer (because I don't have to copy the string data in the first case).
Not exactly sure what you mean by this. 
dburns wrote: char buff[100];
...
const char* p_buff = buff;
myclass.foo(p_buff)
Why use p_buff when you can pass buff directly to the foo() method?
"A good athlete is the result of a good and worthy opponent." - David Crow
"To have a respect for ourselves guides our morals; to have deference for others governs our manners." - Laurence Sterne
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David,
DavidCrow wrote: Why use p_buff when you can pass buff directly to the foo() method?
I could have passed buff in directly, yes. What I was trying to illustrate is that the input parameter might actually be a const char* pointer, but in that case I don't know where the underlying data came from. It could be from a buffer, as in the example, so I would have to copy the data in this case.
Unfortunately, a "quoted string" is also a const char* pointer, so it would naturally choose the same overridden foo. But if it's a "quoted string" then I don't have to copy the underlying data, so the goal is to differentiate between these two cases.
Like I said, probably not possible in C++, just checking.
DB
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Guess you can't use a string type instead of a char*? If you used a string type throughout your application, and if that type used reference counting, then the only strings you would have to copy would be the literals, the others you would simply increase the reference count. This would clearly change your efficiency - no idea if for better or worse.
Peter
"Until the invention of the computer, the machine gun was the device that enabled humans to make the most mistakes in the smallest amount of time."
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 Kind of funny you should suggest that, because that's almost exactly what we have today. Once our string type has copied data from a buffer, then it is ref-counted to avoid further copies. We have a means to specify that the input string is a literal quoted string, in which case no copy of the string data is made at all (and ref-counting is not needed).
However in most cases programmers seem to use the version that copies string data even when they're supplying a literal quoted string. No reason other than they have other things on their mind when writing code, and don't seem to remember such details.
So my goal was to detect this and either automatically be more efficient, or give them a compiler error that forces them to use the more efficient version.
As an update I've found I can use "const" to detect the use of a non-literal buffer in some cases, but not all. For example:
char buff[100];<br />
...<br />
StringClass s1(buff);
const char* ptr = ...;
StringClass s2(ptr);
StringClass s3("hello");
So I would like to distinguish between the s2 and the s3 case (the s2 case should be copied since there's no telling where the pointer is pointing, and the s3 case should not be copied). I don't think C++ is going to let me do that.
Thanks for the ideas...
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Hi,
I have a small problem with my radio buttons. I have a group of three buttons, when I click button 0 everythings fine, but if I click button 1 or 2 and special requirements are not met the software should give a message to the user and reselect button 0. I did it in the BN_CLICKED message handler of the two radio buttons like this:
void CDlgMacroColor::OnReferenceDynamic()
{
if(some condition)
{
m_EditColorRefThreshold.EnableWindow(TRUE);
}
else
{
AfxMessageBox("No Global Reference found! Changing to Local Color Reference.",MB_OK|MB_ICONEXCLAMATION,0);
m_EditColorRefThreshold.EnableWindow(FALSE);
m_iReferenceType = 0;
UpdateData(FALSE);
}
}
m_iReferenceType is the integer determining which radio button is selected.
The problem that occurs is, that with UpdateData(FALSE) a new BN_CLICKED message is sent to the same radio button I just declined (I would accept it if it was sent to the new one, but no, it's sent to the old one) and the user gets the message box twice.
Now my two questions: Why does this happen? and even more important: How can I avoid this?
Thanks in advance
Martin Dietz
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