I currently have a C# project that uses a 32 bit dll. What I am trying to do is to use the dll in a C++ project , unfortunately the dll referenced in the project does not come with a .h or .lib file so I am confused on how I could access the classes in the dll or use the dll file in my project in C++ (Visual Studio 2010) . I read here that if a dll file contains classes its a good chance it might be a COM component.Any suggestions on what I should be looking at in order to integrate and consume methods and objects in that dll.
Update:
I checked if it was a COM by doing an import statement. However I get a "cannot find .tlb file". Then I decided to use dependency walker to check for any exported methods (objects)it seems there are none. I clicked on the main file (which has been highlighted) and couldn't see any exported functions. Any hints on what I should check for next ?. Here is what I get from dependency walker.
With only a .dll and without a corresponding .h or .exp, one place that you might try looking would be the exports table. Tools such as Dependency Walker can show you this information.
One caveat with Dependency Walker is that you'll want to use the right version (x86 or x86_64) for the binary (your DLL). If you're not sure, pick one version and try loading it. Under the CPU column, middle panel, look to see if it says "x64" or "x86" to determine which one you should be using.
With the provided screenshot of Dependency Walker (indicating a dependency on MSCOREE.DLL), I agree with Eugene - this is most likely a .NET library, not a COM library. You will want to check one of the other questions about calling .NET managed code from C/C++.
The dll is most likely a .Net assembly (seeing that it imports mscoree.dll), so you probably want this: How do I call a .NET assembly from C/C++?
Related
As we know, when trying to run a program with some of its dependent DLL missing, the system would complain about "missing dll" error. The approach I'm using to avoid this is to pack all those dependent DLL into the installer, so that the software could run in other devices. Yet with the growing number of dependent DLL, manually search and copy DLL turns out to be such a chore, especially considering that these direct dependent DLL are likely have their own dependencies.
I have known dumpbin, Dependency Walker and Dependencies to track DLL dependencies. But they only list the dependent DLL. I was wondering is there any command/script/tool that could:
recursivly search the dependent DLL of an executable
copy those dependencies to a specified directory
preferably, support exclude DLL from specified directories, like C:\WINDOWS\system32\
To be honest, I don't know if this kind of thing ever exists. If it doesn't, how do you guys deal with this DLL issue?
I have been using InstallAware Express CodeGear Edition under this link http://cc.embarcadero.com/Item/24997
It was no longer continued. But there is a menu there that it finds and locates the depended dll or bpl files, and you create a quick and dirty install project, all copied into one folder. Than you can use them for your application. This is no longer works for me, and I am also looking for another tool for this.
If you find something please let me know.
My basic issue is this: my program (MyProgram.exe) has a dependency on a DLL from another program (OtherProgram), and I'm trying to avoid repackaging a new DLL every time OtherProgram updates. I'd like to have MyProgram.exe link in OtherProgram's DLL when it launches, but I'm not completely sure that Windows allows for this. So if there is some kind of workaround that would also be acceptable.
And just for some background, the platform is Windows 7 x64, and MyProgram.exe runs fine when I create a symlink in the MyProgram.exe project directory to the DLL in OtherProgram's install directory. When I try to run it without the symlink, I get the "program can't start because OtherProgramDLL.dll is missing from your computer" error.
Any advice or links to relevant info is greatly appreciated!
EDIT: Clarification: the DLL is not linked at compile-time, this issue crops up at runtime
There are two types of dynamic linking in the Windows world:
Load-Time linking is when a DLL is loaded automatically when your program starts up. Windows finds this DLL using a specific algorithm I'll discuss below.
Run-Time linking is when you specifically load a DLL by calling LoadLibrary in your code. Similar rules apply as to how the library is found, but you can specify a fully-qualified or relatively-qualified path to control the search.
In the case of Load-Time linking, MS recommends that your program's DLLs are stored in and loaded from the same directory where your application is loaded from. If this is at all workable, this is probably your best option.
If that doesn't work, there are several other options, outlined here. One is to leverage the search order by putting the DLL in either the working directory or the directory where the application was loaded from.
You can change the working directory of an application by:
Create a shortcut to your application.
Bring up the shortcut's properties
Edit the "Start in" property with the directory where the DLL is located.
When you launch your application using the shortcut, it will load the right DLL.
Other options for load-time linking include:
Adding a manifest to your application which specifies where your dependent assemblies are, or,
Setting the PATH.
You could use LoadLibrary, but you would need a way to guarantee the DLL's location. This Wikipedia article provides good example on how to use the DLL after it has been loaded.
You can add the directory where the dll is located to the PATH environment variable.
I have struggled with the same problem and also found a dead end with the suggested methods like LoadLibrary, SetDllDirectory, Qt's addLibraryPath and others. Regardless of what I tried, the problem still remained that the application checked the libraries (and didn't find them) before actually running the code, so any code solution was bound to fail.
I almost got desperate, but then discovered an extremely easy approach which might also be helpful in cases like yours: Use a batch file! (or a similar loader before the actual application)
A Windows batch file for such a purpose could look like this:
#echo off
PATH=%PATH%;<PATH_TO_YOUR_LIB>
<PATH_TO_YOUR_APP_EXE>
/edit: Just saw #SirDarius comment in Luchian's answer which describes that way, so just take my batch code bit as a reference and all credits go to him.
I have the same problem with one application I am working on.
I do not want to use runtime loading because there are tens of functions I would need to manually create function pointer for.
Mr Dibling's mention of manifest file opened a new door for me but I sadly found out that the oldest version of windows that supports the feature is Windows 7. It won't even work on Vista.
Long story short, a friend familiar with Windows Application development told me to look up Delay-Loaded DLL, which turns out to solve the problem perfectly with minimal effort. It delays the loading of DLL library to either the point you manually do, or the first time its function is called. So you just need to add your DLL path to the search path before that happens, where SetDllDirectory helps.
Here is the steps to make it work:
1) Specify the DLL to be delay-loaded to linker, either through your makefile, cmake or VS property page (Linker->Input of VS2015)
2) Call SetDllDirectory at the beginning of your program, before any call to the DLL is made.
Delay-loaded DLL is supported all the way back to VC6.
SetDllDirectory is supported after XP SP1.
Use Symbolic Links to the 3rd Party Executables
I found the approach advocated by Aaron Margosis useful. See:
Using NTFS Junctions to Fix Application Compatibility Issues on 64-bit Editions of Windows
Essentially, create symbolic links to each of the dependent 3rd Party executables. Place these symbolic link files in and amongst your own dependent executable files. Except for filename changes to the targets, the 'soft' symbolic links will resolve the load-time dependencies even as the target of the links are changed by future updates.
I want to emulate an unmanaged dll in c++. Is there a good tool to open and view it's interface?
Thanks
The most commonly used tool is Dependency Walker. This shows the list of exported symbols.
However, it does not show the function prototypes because they are not contained in the DLL meta data. To get that information you need a header file for the DLL. The exception to this statement are DLLs containing a COM/ActiveX component with a type library.
And even if you do have the prototypes, that's not enough to know how to emulate the DLL. You need full documentation for the DLL. And then you probably still have a lot of reverse engineering to do.
I am developing a C++ library that I want to pass on to my team. The library has just one class with a bunch of methods.
So, I have developed the class definition file (X.cpp) and a corresponding class declaration file (X.h).
Here are my questions --
In Visual Studio 2005, whats is the most straight forward way to build this library as a DLL, such that I get the following files:
X.lib : which I can pass to my team so they can link against my library
X.dll : which I can pass to my team for run-time
Instead of a DLL, should I rather be going the static library way ?? If so, how do I go about doing this in Visual Studio 2005 & will this give me a X.lib file that I can pass on to my team ?
Any explanations or references are very welcome.
Thank you very much.
The easiest way to build a DLL, is New->Project->Win32 Console Application. Then on the dialog select DLL and select "Exports Symbols". This will synthesize a dll with a .h, and .cpp file which demonstrate how to export your classes. You can get rid of this .h/.cpp but first import your class add the appropriate #ifndef statements. Now as far as DLL versus Static library if its a single small class, that doesn't change particularly often you might be better off with a static library, its simple, its concise, it doesn't add another dependency which needs to be shipped with your product. A DLL is nice if the code in the .cpp file changes often (ie. the function implementations) because you can just swap in the new DLL.
From your description, it looks like you already have a Visual C++ project (correct me if I'm wrong). If so, when you go into project properties, under "General" you can find "Configuration Type" - switch it to "Static library" or "Dynamic library" as needed.
If you choose "Static library", then you will just get a .lib file that can be immediately used.
If you choose "Dynamic library", and you export any functions from your DLL (e.g. by marking them with __declspec(dllexport)), an export .lib will be generated automatically.
It's hard to tell which option is preferable without knowing the specifics of what you're doing. In general, I'd recommend defaulting to static libraries, because it's usually good enough, and there are more traps when dealing with DLLs (especially ones that export C++ symbols).
I think that, in most cases, a dll is a better choice than a static lib because your team will not have to recompile their code when you distribute a new version of your library.
I struggle with this too sometimes.. because I can't find where the elusive setting is within C++ Project Properties.. So I decided to jot it down for my own sanity as a blog post.
HTH
We have a (pure native C++) .DLL that is build by VS. As clients we have some native C++ applications and a .Net-Wrapper around this DLL written in C++/CLI. Finally there are some client applications for the .Net-Wrapper written in C#.
My problem is that the native.dll must be distributed in a different way than the .Net world works and the VS does not keeps track of that DLL.
So to let all my C# Apps work correctly I have to copy it to each executable directory or put it somwhere in %PATH% (which I would avoid on developer computers since they may want to start different apps with different versions of the DLL).
Even bigger problems occur if there are UserControls that reference the Wrapper-DLL: You have to copy the DLL to VS's directory or again to %PATH%.
But the worst case occurs with our Translator tool. This tool keeps track of .Net-Assemblies and packs them into Translator-packages that can be send to an external translator. As far as I know there is no way to put the native .DLL into that package!
So I plan to link the native DLL statically into the .Net-Wrapper which would solve my problems.
But for our Native applications this native DLL must still be a DLL.
So I have two options:
Make two projects of that (one that generates a static library; and one that creates a dynamic one => I try to avoid this)
Find a solution to link DLLs statically
Find a way to let VS generate two outputs from one project
In the C++ project file for the dll, create two configurations, one that generates a DLL and one that generates a .lib. Two projects are not necessary, since any .NET/C++ project can support multiple build configurations (this is how Release and Debug versions build differently).
Another option is to have two projects, one project will output a .lib which can be statically linked, and a second project which will output a .dll and will have your .lib as dependency, you should add .def to your .dll with the symbols that you are planning to export, or else it will be empty.
Pick up a copy of DLL to Lib (Edit: If you can't find a cheaper option)
You can generate a dll and export the entry point to a lib using dllexport, this is explained here
http://msdn.microsoft.com/en-us/library/3y1sfaz2.aspx