I am making a win32 console app using msvc++ that is going to use a really simple dll. I put my .lib and header for my dll (my dll only has one header) into my console applications folder.
When I run it, I don't get any compile or linking errors, but when the app is actually open, it says it cant find the dll. When I put the .dll file into the console app's folder and run, it actually works. I would like to know why this happens??????
Look at this link:
Dynamic-Link Library Search Order
Windows has a DLL search order. You can change it by functions specified in the above link.
Your import library is used to define information about functions in your DLL and so. You can use LoadLibrary("myDLL.dll") function to load DLL without header.
In this case you must use GetProcAddress(module, "function_name") function to get function adresses in your DLL.
GetProcAddress function
and here is the link where is some solution for GetProcAddress():
Calling functions in a DLL from C++
Related
I'm using MYSQL library, and libmysql.lib /.dll.
My program cannot be working without the libmysql.dll
When I'm trying to run my project without the dll I'm getting that error message.
What I'm basically want to do is to put that dll in my .exe file.
build the .exe file with that dll and make the program read it from himself.
I mean, give the program to people with that dll inside.
It is possible ?
I tried this section: embed DLL in MFC C++ EXE?
But the program still asking for the dll .. (But I do see that the size of the .exe has been changed) so that dll has been added.
But the program still asking for the libmysql.dll ..
All the point is to use it inside the .exe file..
thanks.
What you are asking for cannot be done if you statically link to the DLL at compile-time. You need to dynamically link to the DLL at run-time instead, either by explicit calls to LoadLibrary() and GetProcAddress() to access the DLL functions directly, or by utilizing your compiler's delay-load functionality (which uses LoadLibrary() and GetProcAddress() internally, but hides that fact from your code). Either way, you can then store the DLL in your EXE's resources at compile-time, then extract the resource to a temporary file at run-time and load/use it as needed (you can't use the DLL from inside the EXE's resources directly. Well, there is a way to do it, but it is a VERY complicated and advanced technique, as it requires implementing your own executable loader that basically mimics what the OS's built-in executable loader already does). When you are done using the DLL, you can unload it from memory and delete the temp file.
I don't know how to do the following:
I'm using MS Visual C++ 6.0
I have a Win32 DLL project which is compilable.
I have another project, this time a Win32 Console project which uses
the DLL by including it's header file and linking the .lib file of
the DLL.
Now I want to have another project, similar to the second BUT without using the header file and the lib file.
Is that possible? Everywhere I read you need either dll+lib+h or dll+h. If thought if you know the interfaces, a DLL file is sufficient?
Btw, by "using a DLL" I mean, using the Classes and Functions defined in the DLL.
It is possible if you just have plain "extern C" functions. If this is the case the approach could be loading the dll with LoadLibrary, and then import each function with GetProcAddress, of course you need to know the function signature to create a properly declared function pointer. Using classes per contrary is almost impossible.
If your DLL contains classes, there are good chances that it is a COM component.
If this is the case, the #import directive (that you use like #include) builds some temporary include files containing the interface details. You should use COM to access your objects.
Otherwise, if you have a 'plain' DLL with C++ classes, you could access the exported symbols using linker: instruct it to dump the map (see here), to know the mangled names. But I don't think that's possible to build manually the interface...
This question is regarding dynamic linking of libraries and usage of dynamic linking of libraries in application.
For example we are devloping an application using C++ using Visual studio environment.
Here for include header files we specify in Additional Include Directories, and
in Additional Dependencies: Mylibrary.lib
in Additional Libraries Directories: We specifies path of libraries
And in Windows we also have "LoadLibrary" API which is used to load dynamically linked ibrary.
My question is
when we include dll in Additional dependencies libraries why we should use "LoadLibrary" API?
When we should use "LoadLibrary" API?
Thanks!
LoadLibrary lets you continue program execution if the dll is not on the running machine. It returns an error status that can be checked and execution can be continued.
Also, linking lets you do stuff like use classes from the other binary & others. LoadLibrary only lets you find functions via GetProcAddress.
Imagine that you have a software that for example needes at a determined time to convert
Internet network address into strings.
On windows vista or later you can use the "InetNtop" function that is also able to deal with ipv6, but if you link directly to the DLL your program will no work on lower OS (ex: windows xp).
So the best solution would probably be making 2 DLL's one that used "InetNtop" and another that used for example "inet_ntoa".
Then your "main" program would do at runtime a LoadLibrary of the "InetNtop DLL", or the "inet_ntoa DLL", according to the OS that he his installed.
You asked that you can include dll in Additional dependencies libraries, and then why to use loadlibrary.
First lets clear the understanding:
While linking statically, A programmer is needed to add the .lib file to
Additional library dependency, which is linked to the caller program at compile time,
However, Dlls are loaded dynamically, hence you need not to add dlls in Additional library dependency when you are using LoadLibrary ie; if you are linking the Dll explicitly you are not needed to give your dll path in Additional library dependencies.
Please note:
using LoadLibrary you will be able to Get the Dll handle, which you can call the exported function using GetProcAddress.
refer:
https://msdn.microsoft.com/en-us/library/windows/desktop/ms684175(v=vs.85).aspx
I am attempting to delay load wintrust.dll and crypt32.dll in my application (these are used to perform digital signature/publisher checks in a DLL). I am using VS2008. After adding these two DLLs as entries in the Delay Load property in the Linker section of my project properties, I still get LNK4199 warnings that nothing was loaded from the DLL and LNK2019 errors unable to resolve symbols such as WinVerifyTrust.
Adding the following as entries to Additional Dependencies alleviates this problem: crypt32.lib and wintrust.lib. I now get no issues with linking. However, what I am wondering is how do I make sure this isn't being linked to the static lib? I do not want to link to the static lib because of potential licensing issues. I want to dynamically load the DLLs that are installed in Windows, and was hoping DelayLoad could help me do this without having to resort to LoadLibrary and GetProcAddress function calls.
Any information about all the different library usage/linking options would be greatly appreciated!
Thanks.
There is no static .lib for these. The SDK libraries are always import libraries, not static .libs because the corresponding Windows API lives in a DLL. No need to worry about this.
Delay loading doesn't free you from having to link to the lib file. Normally, DLLs are loaded as soon as your application starts. Delay loading just delays this until the first time you call a function from that DLL. Either way, you need to link to the lib file so that the linker can verify that the functions you are calling are actually present in the DLL.
If you don't want to link to the lib files, your only way out is to use LoadLibrary and GetProcAddress.
One tool that can help you determine if things are being linked as you expect is DependecyWalker: http://www.dependencywalker.com/ - specifically, in the case of delay-loads it marks them with a special symbol.
You may want to look at the Win32 API methods LoadLibrary and GetProcAddress.
It's pointed out by this answer:
Failed to link mysql5.1.39\bin\libmySQL.dll
But I don't understand why,.dll is essentially the same as .lib except for there is only one copy of it used by different processes.
Does it have anything to do with the IDE?I'm using visual c++ 2008 express
UPDATE
Anyone know a free tool to convert .dll into .lib in windows?
You are wrong on two counts. Firstly, DLLs and LIBs (static libraries) are very different beasts. The LIB you are talking about (I think) is the export library, which is simply a list of names in the DLL. This library is typically produced when the DLL is compiled and is shipped with the DLL if the DLL is intended to be linked to by other developers.
To use a DLL with a modern IDE (I don't use VS) you typically include the matching .LIB (export library) in the project. At run-time you must make sure the DLL is available to your program - the simplest way to do this is to put the DLL in the same directory as the executable.
And secondly, DLLs can be used with C++.
DLL are specific windows executables which load on runtime. Their equivalent in Linux is the *.so .
If you want to understand what's the difference between a DLL and a static lib see here.
Main reason has probably something to do with dll-file being an output of the linker (link.exe). This command line utility doesnt know how to read dlls, only how to write them.
Actually sometimes .lib-files contain more than a list of functions. For example libpng.lib works as a standalone file, without any dll file.
In order to use a DLL in C/C++ you need to link with what is called an import lib. This is a small .lib that contains the names/ordinals the DLL exports in a format that the linker understands. Once this has been linked in, the resulting binary will be able to use the DLL. If you do not have the appropriate import lib, your C/C++ compiler should come with a tool to generate one from the DLL.
You can use the following analogy to understand the difference between a dll and a lib file.
the dll is like the source .cpp file while the lib is the header .h file.
While this is not exactly true, the DLL holds the executable code while the LIB file tells the linker how to glue the code together.
It is also possible (in some cases) to generate the lib from the dll. Basically, all you need to know to call a function is the function entry point in the dll, the number of parameters and the size of each parameters. Sending relevant information is then your own problem.