Loading DLL with specific path

doublenach · 02-08-2010, 07:17 PM

Hi all,

I have a C project in which I need to load a dll, using LoadLibrary() I am able to load it if the dll is on the executable folder or in the system32 folder, but I cannot load it from a specific path. In my case, my app will use a dll located in Program Files\Common Files and LoadLibrary doesn't load when I write the full path.

How do I do this?

Regards,
Rafael

**Bubba** · 02-08-2010, 11:50 PM

LoadLibrary() will fail if the path is invalid. If it is not loading the DLL then it cannot find it. The DLL link process starts in the same folder as your EXE. If the DLL cannot be found there then Windows looks in the System32 folder. If it cannot be found there a message box will popup stating it could not find a component necessary to run your EXE.

Another way that LoadLibrary() can fail is if the DLL has not been registered on the computer via regsvr32. DLLs that have not been registered for use on the machine cannot be linked with, used, or dynamically loaded. If LoadLibrary() returns a NULL HMODULE then you must call GetLastError() to get the error information. The Platform SDK explains this in great detail.

http://msdn.microsoft.com/en-us/libr...75(VS.85).aspx

_Mike · 02-09-2010, 11:34 AM

Quote:

Originally Posted by doublenach

In my case, my app will use a dll located in Program Files\Common Files and LoadLibrary doesn't load when I write the full path.

Sounds like the path is incorrect or your application doesn't have read access to that directory. What does GetLastError() say?

Quote:

Originally Posted by Bubba

The DLL link process starts in the same folder as your EXE. If the DLL cannot be found there then Windows looks in the System32 folder. If it cannot be found there a message box will popup stating it could not find a component necessary to run your EXE.

Unless you specify an absolute path. Even says so in the link you posted:

Quote:

If the string specifies a full path, the function searches only that path for the module.

Quote:

Originally Posted by Bubba

Another way that LoadLibrary() can fail is if the DLL has not been registered on the computer via regsvr32. DLLs that have not been registered for use on the machine cannot be linked with, used, or dynamically loaded.

Not true.
Isn't the use of regsvr32 to store a registry mapping between COM/ActiveX GUIDs and their respective dll location?

doublenach · 02-09-2010, 01:01 PM

Hi,

thanks for the reply, as suggested I tried GetLastError and I received 'The specified module could not be found.'

My code looks like this:
LoadLibrary("C:\Program Files\Common Files\example.dll");

The dll is there, if I copy/paste into the file browser there it is. I am thinking it is the syntax, how should it be? I really searched this but I can't find any example on microsoft website and also couldn't find any other code example on the internet that loads a dll from a specific path.

Regards,
Rafael

**nvoigt** · 02-09-2010, 01:40 PM

You need to use double backslashes, as always:

LoadLibrary("C:\\Program Files\\Common Files\\example.dll");

Please note that your code will only run on machines that are installed in English. "Program Files" is localized in XP

brewbuck · 02-09-2010, 01:50 PM

Quote:

Originally Posted by Bubba

Another way that LoadLibrary() can fail is if the DLL has not been registered on the computer via regsvr32. DLLs that have not been registered for use on the machine cannot be linked with, used, or dynamically loaded. If LoadLibrary() returns a NULL HMODULE then you must call GetLastError() to get the error information. The Platform SDK explains this in great detail.

That's untrue -- DLLs do not need to be registered. regsvr32 is normally used to register and unregister DLLs which provide system-level services, such as COM or ActiveX components. If you don't believe me, try it -- create a simple DLL project which exports a function, build the DLL, and call LoadLibrary() on it. It works fine.

_Mike · 02-09-2010, 04:48 PM

Quote:

Originally Posted by nvoigt

You need to use double backslashes, as always:

LoadLibrary("C:\\Program Files\\Common Files\\example.dll");

Please note that your code will only run on machines that are installed in English. "Program Files" is localized in XP

Indeed, and so is "Common Files". And it also depends on if you're on a 32 or 64-bit OS.

If you want version-independant code, use the %CommonProgramFiles% environment variable together with ExpandEnvironmentStrings Function (Windows)
Example:

Code:

TCHAR *path = L"%CommonProgramFiles%\\microsoft shared\\Windows Live\\WindowsLiveLogin.dll";
TCHAR *expandedPath = NULL;
// Set length to 0 the first pass to find out required buffer length
DWORD numChars = ExpandEnvironmentStrings(path, expandedPath , 0);
expandedPath = new TCHAR[numChars];
ExpandEnvironmentStrings(path, expandedPath, numChars);
HMODULE hm = LoadLibrary(expandedPath);
delete [] expandedPath;

(proof of concept code, add your own error handling)

**Bubba** · 02-09-2010, 07:22 PM

Quote:

That's untrue -- DLLs do not need to be registered.

Interesting. I actually ran into this problem recently and regsvr32 fixed it. But again I am probably making a bad assumption that the DLL is a COM or ActiveX object since that is what I am used to. But yeah it would not make sense to force registration of every DLL. My apologies.

Quote:

Unless you specify an absolute path. Even says so in the link you posted:

Which is why I posted the link. There is a lot of good information there about the issue. Personally I never specify absolute paths so have never ran into this particular problem while using LoadLibrary().

_Mike · 02-09-2010, 09:10 PM

Quote:

Originally Posted by Bubba

Which is why I posted the link. There is a lot of good information there about the issue. Personally I never specify absolute paths so have never ran into this particular problem while using LoadLibrary().

Ah okey, then I misunderstood your post. I thought you meant that you cannot use absolute paths. Sorry.

adeyblue · 02-09-2010, 10:23 PM

If you need more debugging info than just GetLastError() for failed dll loads, here's how you get some internal debug spew from Windows.

doublenach · 02-13-2010, 06:44 AM

Thank you all very much, I am now able to load the DLL using double backslashes.

Rafael

02-08-2010, 07:17 PM	#1
doublenach Registered User Join Date: Feb 2010 Posts: 3	Loading DLL with specific path Hi all, I have a C project in which I need to load a dll, using LoadLibrary() I am able to load it if the dll is on the executable folder or in the system32 folder, but I cannot load it from a specific path. In my case, my app will use a dll located in Program Files\Common Files and LoadLibrary doesn't load when I write the full path. How do I do this? Regards, Rafael
doublenach is offline

02-08-2010, 11:50 PM	#2
Bubba Super Moderator Join Date: Aug 2001 Posts: 7,813	LoadLibrary() will fail if the path is invalid. If it is not loading the DLL then it cannot find it. The DLL link process starts in the same folder as your EXE. If the DLL cannot be found there then Windows looks in the System32 folder. If it cannot be found there a message box will popup stating it could not find a component necessary to run your EXE. Another way that LoadLibrary() can fail is if the DLL has not been registered on the computer via regsvr32. DLLs that have not been registered for use on the machine cannot be linked with, used, or dynamically loaded. If LoadLibrary() returns a NULL HMODULE then you must call GetLastError() to get the error information. The Platform SDK explains this in great detail. http://msdn.microsoft.com/en-us/libr...75(VS.85).aspx __________________ If you aim at everything you will hit something but you won't know what it is. Last edited by Bubba; 02-08-2010 at 11:54 PM.
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02-09-2010, 01:01 PM	#4
doublenach Registered User Join Date: Feb 2010 Posts: 3	Hi, thanks for the reply, as suggested I tried GetLastError and I received 'The specified module could not be found.' My code looks like this: LoadLibrary("C:\Program Files\Common Files\example.dll"); The dll is there, if I copy/paste into the file browser there it is. I am thinking it is the syntax, how should it be? I really searched this but I can't find any example on microsoft website and also couldn't find any other code example on the internet that loads a dll from a specific path. Regards, Rafael
doublenach is offline

02-09-2010, 01:40 PM	#5
nvoigt the hat of redundancy hat Join Date: Aug 2001 Location: Hannover, Germany Posts: 2,769	You need to use double backslashes, as always: LoadLibrary("C:\\Program Files\\Common Files\\example.dll"); Please note that your code will only run on machines that are installed in English. "Program Files" is localized in XP __________________ hth -nv She was so Blonde, she spent 20 minutes looking at the orange juice can because it said "Concentrate." When in doubt, read the FAQ. Then ask a smart question.
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02-09-2010, 10:23 PM	#10
adeyblue I have a hat!? Join Date: Apr 2008 Posts: 178	If you need more debugging info than just GetLastError() for failed dll loads, here's how you get some internal debug spew from Windows. __________________ Desktop Heap Monitor for Vista/7 A solution to Visual Studio 2005/8 runtime problems Getting Kernel Thread Call Stacks
adeyblue is offline

02-13-2010, 06:44 AM	#11
doublenach Registered User Join Date: Feb 2010 Posts: 3	Thank you all very much, I am now able to load the DLL using double backslashes. Rafael
doublenach is offline

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