C / C++ / MFC

24-Aug-06 0:03

I made an application which used a dll and loads it dynamically. If dll is not present an exception raises. All i want is if dll is not present it should be known at the Loadlibrary(..) call and i could handle that exception. I have specified lib fiel of that dll in the tools->project settings->link tab. Is there any other way?

Thank you

KIRAN PINJARLA

Michael Dunn24-Aug-06 0:12

Michael Dunn

24-Aug-06 0:12

LoadLibrary() returns NULL if it can't load the DLL. If you're getting an exception, I bet you're not checking the return value from LoadLibrary() and blindly using it.

--Mike--
Visual C++ MVP Cool | :cool:

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Kiran Pinjala24-Aug-06 0:20

24-Aug-06 0:20

Michael Dunn wrote:
I bet you're not checking the return value from LoadLibrary() and blindly using it.

U lost.
I am checking the return value. Here is my code.

if((h = LoadLibrary("..\\Output\\DllOne.dll")) == NULL)<br />
{<br />
	AfxMessageBox("Failed To Load Library");<br />
	return;<br />
}<br />
COne one;<br />
one.ShowMsg();<br />
FreeLibrary(h);

Let me explaint what is happening exactly. My client application is a dialog based app. I wrote the above code in a button press. It should load and return value when button is presse.
But the problem is even the dialog is not being displayed. Even before that its showing the exception
"THE APPLICATION FAILED TO START SINCE ATHE one.dll IS NOT FOUND. REINSTALLING THE APPLICATION MAY FIX THE PROBLEM"
right after executing x.exe file.

Can u help me now?

KIRAN PINJARLA

prasad_som24-Aug-06 0:29

prasad_som

24-Aug-06 0:29

kiran.pinjarla wrote:
"THE APPLICATION FAILED TO START SINCE ATHE one.dll IS NOT FOUND. REINSTALLING THE APPLICATION MAY FIX THE PROBLEM"

This must not be using CAPS, for sure.

You must be be implicitely linking that dll, too. If you are using LoadLibrary, its not needed.
You need to use either of them.

Prasad
Notifier using ATL

Kiran Pinjala24-Aug-06 0:41

24-Aug-06 0:41

prasad_som wrote:
You must be be implicitely linking that dll

no iam not.I am only using LoadLibrary() to load.

KIRAN PINJARLA

Cedric Moonen24-Aug-06 0:48

24-Aug-06 0:48

kiran.pinjarla wrote:
No I am not

Yes you are. From your first post:

kiran.pinjarla wrote:
I have specified lib fiel of that dll in the tools->project settings->link tab

That means implicitely linking to the dll. Remove that and all should be ok.

-- modified at 6:48 Thursday 24th August, 2006

Cédric Moonen
Software developer

Charting control [Updated - v1.1]

Kiran Pinjala24-Aug-06 0:51

24-Aug-06 0:51

Cedric Moonen wrote:
Remove that and all should be ok.

I removed it. It showing Unresolved symbols error now.

KIRAN PINJARLA

Cedric Moonen24-Aug-06 0:58

24-Aug-06 0:58

kiran.pinjarla wrote:
It showing Unresolved symbols error now.

Please when asking a question be more explicit and detail your problem.

Did you include header files coming from the library ? Where some classes are defined ? If yes, you need to remove them.
When using explicit linking to a dll, you don't include anything (lib, headers, ...) in your project. You just call LoadLibrary and GetProcAddress with the name of the function you want to retrieve. And that'is.

Cédric Moonen
Software developer

Charting control [Updated - v1.1]

Kiran Pinjala24-Aug-06 1:06

24-Aug-06 1:06

Thnak you for ur reply.
I am not exporting a function in my dll. I am exporting a class and I am instantialing it in the client application.

if((h = LoadLibrary("..\\Output\\DllOne.dll")) == NULL)<br />
{<br />
    AfxMessageBox("Failed To Load Library");<br />
    return;<br />
}<br />
COne one;<br />
one.ShowMsg();<br />
FreeLibrary(h);

If i remove the header file its showing an error.
error C2065: 'COne' : undeclared identifier
How to proceed.

KIRAN PINJARLA

Cedric Moonen24-Aug-06 1:10

24-Aug-06 1:10

You cannot export a class explicitely (or at least not that way). Why do you want to load the dll explicitely ? Just load it implicitely (put the lib in the project settings like you did and add the header and source file of your class to your project). And that's it. Do you have the source file of your class ?

Cédric Moonen
Software developer

Charting control [Updated - v1.1]

prasad_som24-Aug-06 1:06

prasad_som

24-Aug-06 1:06

I think COne you mentioned earlier is exported class.
Let implicit linking be there, and you can use it directly,but make sure dll is in projects directory,or windows directory, where it can be searched by system.
And before posting make sure , you read this throughly .

Prasad
Notifier using ATL

Kiran Pinjala24-Aug-06 1:21

24-Aug-06 1:21

prasad_som wrote:
Let implicit linking be there,

Is it not possible to instantiate the imported class and callin its functions with explicit linking?

KIRAN PINJARLA

Cedric Moonen24-Aug-06 1:24

24-Aug-06 1:24

No (as I already said before). When you load a dll explicitely, you first 'load' the dll with LoadLibrary but that doesn't imply anything. You have just loaded the dll in memory, next you need to retrieve the address of a function by calling GetProcAddress so that you can call a function from inside your dll. See, how are you gonna 'get' your class that way ??

Why don't you simply go with implicit linking ? It is much more easier to do and everything is managed for you. What is the problem there ?

Cédric Moonen
Software developer

Charting control [Updated - v1.1]

Waldermort24-Aug-06 4:19

Waldermort

24-Aug-06 4:19

You can't export a class directly, you can can make a wrapper to do a similar thing. Inside the dll you would need to instead export a function which would initialise the class for you and return a pointer to it.

Kiran Pinjala24-Aug-06 20:04

24-Aug-06 20:04

waldermort wrote:
instead export a function which would initialise the class for you and return a pointer to it

Thank you so much. This is the solution for which i have been asking for.
One again thank you waldermort.

KIRAN PINJARLA

Kiran Pinjala24-Aug-06 20:57

24-Aug-06 20:57

Ok i did it and got the pointer of the class form dll exported function.
Now how to call the member functions of that class?
Note: we are linking the dll by LoadLibrary(explicitly) only.

KIRAN PINJARLA