I have the following declaration in a Module:
Private Declare Function gzopen Lib "ZLIB.DLL" (ByVal filePath As String, ByVal mode As String) As Long
The following code line in a function fails, with a 'File Not Found: ZLIB.DLL' error:
lGZFileHandle = gzopen(sPath, "rb")
I'm aware that ZLIB doesn't need to be registered. My question is, where does ZLIB.DLL need to live in order for my code to work? I also know that this code is working on another machine. Currently I have ZLIB.DLL in the same folder as the application exe.
UPDATE
To my relief, the code does work when compiled. But does not work whilst running in the IDE (it does on a different machine). I still have ZLIB.DLL in the application folder.
This means that the application path must be being checked for loading the DLL.
To get around this I have tried:
Private Declare Function SetDllDirectory Lib "Kernel32" Alias "SetDllDirectoryA" (ByVal path As String) As Long
and then in the function:
SetDllDirectory App.path
This seems to allow the DLL to load, but I then get a 'Bad DLL calling convention' error instead. The plot thickens.
SOLVED
The answer seems to be here: http://www.zlib.net/DLL_FAQ.txt. It's a case of RTFM I suppose.
So, bizzarely whilst in the IDE, the STD_CALL convention is in force, but once compiled the C style calling convention suffices. It still doesn't explain why it works on a different machine in the IDE. Ho hum.
Thanks all for pointing me in the right direction.
VB6 strayed a bit from the search protocol suggested by Ken (this link is the quick reference).
The usual problem is that the .exe path (search location #1 on the list) is not the path of your VB program, but rather the VB6 IDE. So putting the DLL in the location of your VB program is no good -- unless you change the 'Start In' location of your VB6 shortcut to point to that location.
Alternately, you can put the DLL in one of the other locations specified in my link.
When running through the Visual Studio IDE, all relative files need to be placed in the following folder:
C:\Program Files\Microsoft Visual Studio\VB98\
This is because the exe that is running while debugging resides in that folder. This will allow you to debug without changing any paths.
ZLib has to be in the standard DLL load search path. See the MSDN LoadLibrary documentation for specifics on the way DLLs are found and the order of the search for them.
Are you sure ZLIB doesn't have to be registered?
I suggest you register it and try again.
EDIT
Try putting the DLL in your System folder. I believe your program will check there for it.
Related
To start, I know this question has been asked a million times all over the place, but as I have no experience with VB/Visual Studio, I can't find a solution that I can make sense of.
I am creating a new VB.net project(solution?), and am making calls to functions from a C library that are in a dll file. The dll file does have a pdb file and they are both stored at the same location.
In the code below it shows how I declare the functions in my VB.net code, but I have not figured out how to attach the pdb file to the project.
Declare Function InitRelay Lib "Z:\Devel\RelayAPI\Debug\RelayAPI.dll" (ByVal setbaud As Action(Of Short), ByVal getit As Func(Of Short, Short), ByVal putit As Action(Of Short), ByVal flushit As Action, ByVal delay As Action(Of Short)) As Byte
Declare Sub FreeRelay Lib "Z:\Devel\RelayAPI\Debug\RelayAPI.dll" ()
...
I am getting an exception somewhere in the DLL file, but the way I have it set up, I can not debug the dll file. Whether its adding breakpoints, or print statements, I need a way to see where in the dll the project fails.
Questions I have looked at:
How to debug a referenced dll - I tried following the menu path given in the accepted answer, but when I go to Project >> Project Properties I see no Build option. It also says I can load symbols directly in the IDE if I don't want to copy any files, but I cannot find an explanation on how to do it. EDIT - As Plutonix says below, C# Build is the equivalent of VB's Compile tab. I checked and my Debug Info is set to Full, so this does not solve my problem.
Debugging a third-party DLL in Visual Studio? - This talks about a DLL in a .NET language but mine is in C. It also only tells you how to view the code, which I already can do. I have access to the .c and .h files that are used to create the dll, I just cannot debug them at runtime.
When you debug a DLL, you can start debugging from:
The project used to create the executable that calls the DLL.
- or -
The project used to create the DLL itself.
There are a couple of ways to debug a reference DLL file using VS 2013, so here the method Microsoft uses
-->To specify an executable for the debug session
In Solution Explorer, select the project that creates the DLL.
From the View menu, choose Property Pages.
In the Property Pages dialog box, open the Configuration Properties folder and select the Debugging category.
In the Command box, specify the path name for the container. For example, C:\Program Files\MyApplication\MYAPP.EXE.
In the Command Arguments box, specify any necessary arguments for the executable.
Here I included 2 different methods for debugging a DLL file directly from Microsoft.
1> http://msdn.microsoft.com/en-us/library/605a12zt.aspx (Native Mode)
2> http://msdn.microsoft.com/en-us/library/kbaht4dh.aspx (Mixed Mode)
If this was anyhelp to you or solved your problem please make sure to drop a "vote up"
Ref. All information is from personal experience and Microsoft
I am currently trying to add control to a Power Analyzer in an excel tool. The company provides USB drivers and the appropriate modules and DLLs. I added the DLLs to the System32 folder to ensure they were read in the path. After importing the modules and trying to run the program, I get the error "File Not Found". I then tried to hard code the location of the DLL and I received the same error.
I've looked around the internet and the only issue I could find was possibly a dependency missing from the DLL. An example of the line I'm trying to use is:
Declare Function TmSend Lib "tmctl.dll" (ByVal id As Long, ByVal msg As String) As Long
This line is apart of the module provided by the manufacturer. Is there something I'm missing to get this to work? I want to make sure before I contact the manufacturer.
EDIT:
It appears that the manufacturer uploaded a corrupt DLL causing the issue to arise. When checking the file with Dependency Walker, it failed to even read the DLL.
I see from your question that you've tried all the normal things (making sure the dll is on your path &c.)
You now need to examine the dll carefully. Download this: http://www.dependencywalker.com/
Then use it to open your dll. All the missing dependent dlls will be clearly displayed. Put those on your path too and you're done.
(To clear up some confusion: you will not need to register this dll or add a reference to it.)
I was add to my program reference to dll and it's work good.
Declare Function adc11_get_driver_version Lib "C:\example.dll" () As Integer
but I want to write the specific location of the dll from file(config file) and replace the "C:\example.dll" by string
how can I do this?
thanks
Saar
I think you need to do dynamic PInvoke. One way to do this is using the LoadLibrary function to load the library before .Net tries to find it. You can find some sample code here.
If you leave out the location completely, it will load it based on the current directory of the application. If it's not there, then it looks in the PATH.
If you want to do something more complex, then you need to write the LoadLibrary and GetProcAddress calls yourself in your own proxy.
Some guidance here:
http://www.codeproject.com/KB/cs/dyninvok.aspx
Im working with a CD722UN Customer Display for our POS application.
it comes with a USB2.0 connection and a installation package containing a driver ect..
now, for my application. how should i do when i want to access this driver?
at the moment i'm using the "CD722UN application"s .dll path but that can warry from clients OS ect..
Declare Function opencd722usb Lib "C:\Program\cd7220 USB\cd722dusb.dll" () As Boolean
Declare Function writecd722usb Lib "C:\Program\cd7220 USB\cd722dusb.dll" (ByRef dataoutput As Byte, ByVal Length As Integer) As Integer
Declare Function readcd722usb Lib "C:\Program\cd7220 USB\cd722dusb.dll" (ByRef DataInput As Byte, ByVal size As Integer) As Integer
Declare Function closecd722usb Lib "C:\Program\cd7220 USB\cd722dusb.dll" () As Boolean
my first thought was to first check if there was a device installed in the device manager and somehow use the driver from there???
or
distribute the .dll inside our application folder and use
searchpath ""installed directory"\cd722dusb.dll"
what is the best solution?
thanks in advance!
Figuring out how to access the device yourself is not typically a good idea when you have zero documentation on how to do so properly. There are too many possibilities and the code can be quite awkward in a managed language. You probably can't even get any documentation if the supplier already provides an access DLL.
The odds are pretty good that this DLL will work if you simply copy the DLL into the same folder as your EXE. Try that first, only the DLL name is required in the Declare statement. Look in the install directory for other DLLs that might need to be copied as well if you have trouble. The next option is to P/Invoke the SetDllDirectory() function if you can discover the path at runtime. The next option is to have the installer add the directory that contains the DLL to the system PATH environment variable. Hard-coding the path is your last resort.
I'm racking my brain trying to come up with an elegant solution to a DLL load problem. I have an application that statically links to other lib files which load DLLs. I'm not loading the DLLs directly. I'd like to have some DLLs in another folder other than the folder that the executable is in. Something like %working_folder%\dlls - I'd rather not have dozens (yes ... dozens) of DLLs in my %working_folder%.
I'm trying to develop something that is part of the main app that will adjust the search path # startup. The problem I'm running into is that this new custom DLL path isn't in the system search path. When I start the app it crashes (STATUS_DLL_NOT_FOUND) because the necessary DLLs are not in the appropriate places. What I'd like to do is to check # startup if this new custom DLL folder is in the process environment variable search path and if not add it. Problem is, the application attempts to load all these DLLs before the app executes one line of code.
How do I fix this? I've considered writing a help app that starts first, adjusts the environment variables appropriately and the launches the main app via CreateProcess. This will work I'm sure of it but it makes things difficult on the developers. When they debug the main app they're not going to launch a helper app first - not that they could even do that.
I've tried the registry app path feature with no success. Same chicken and egg problem as before.
What can I do here?
I found Matthew's answer worked for me.
In visual studio 2012 goto your project properties and in
Configuration Properties->Linker->Input->Delay Loaded Dlls
add each dll file that you want to not load until needed.
Although it no longer needs to run before main, this is my code to set the new search path
class RunBeforeMain
{
public:
RunBeforeMain()
{
const TCHAR* dllPathEnvName= name of env variable to directory containing dlls
const TCHAR* pathEnvName= TEXT("Path");
TCHAR newSearchPath[4096];
::GetEnvironmentVariable(dllPathEnvName, newSearchPath, MAX_PATH);
//append bin
_tcscat_s(newSearchPath, MAX_PATH, TEXT("bin;"));
size_t length = _tcslen(newSearchPath);
//append existing Path
::GetEnvironmentVariable(pathEnvName, newSearchPath + length, 4096-length);
::SetEnvironmentVariable(pathEnvName, newSearchPath);
}
};
static RunBeforeMain runBeforeMain; //constructor code will run before main.
[Edit - after re-reading the question I see that the problem you're having is that the DLLs are getting loaded before main starts]
I'm guessing that those libraries are written in C++ and are loading the DLLs from the constructor of some objects in global scope. This is problematic. Allow me to quote Yossi Kreinin:
Do it first thing in main(). If you use C++, you should do it first thing before main(), because people can use FP in constructors of global variables. This can be achieved by figuring out the compiler-specific translation unit initialization order, compiling your own C/C++ start-up library, overriding the entry point of a compiled start-up library using stuff like LD_PRELOAD, overwriting it in a statically linked program right there in the binary image, having a coding convention forcing to call FloatingPointSingleton::instance() before using FP, or shooting the people who like to do things before main(). It’s a trade-off.
[Original answer below]
See this page for the search algorithm used for loading DLLs. You can use SetDllDirectory() to add a directory to the DLL search path.
You also should be able to add a directory to the PATH environment variable using GetEnvironmentVariable() and SetEnvironmentVariable().
Another option is to change the current working directory to the folder containing the DLLs with SetCurrentDirectory(). Just make sure to change the working directory back after loading the DLLs if you ever load any files using relative filenames.
My recommendation is to use delayload linking for the DLLs and call SetDllDirectory() early enough so it can find them when the methods/functions are invoked.