I'm curious about how Dynamic Linking works on windows. Since we CAN NOT link to a directly, windows usually link your executable to a LIB file which contains the stub of functions exported by the DLL. Does this type of linking results in LoadLibrary and GetProcAddress at runtime? If not, how does the linking work internally?
The answer is maybe.
The default method is to create an Import Table, which lists all required DLL's and the functions used from there. This table is parsed directly by the OS. It will probably reuse some of the same code behind LoadLibrary for that. It most likely will not use the code from GetProcAddress but prefer to do a single bulk lookup of all necessary functions.
However there's an MSVC feature called delay-loading. With this feature, MSVC++ will not build such an import table, but insert actual LoadLibrary and GetProcAddress calls. The benefit is that these calls are made at the latest possible moment. While you don't need a particular DLL, it's not loaded. This can accelerate program start up.
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I have my program (.exe) and it depends on 3 DLLs to work, but, I want to hide these DLLs, is there any way for me to "put them in .exe" these dlls? Only have the .exe,is there any method to do this?
Info:
Program's ling: C++
DLLs: {libcrypto-1_1-x64, libcurl-x64, libssl-1_1-x64}
If you use the static versions of the libraries, their code will be compiled directly into your EXE, and then you won't need DLLs at all.
But, if you need to use DLLs, then you can compile them into your EXE's resources, and then extract them at runtime to temp files before using them. You won't be able to statically link to any of the DLL functions at compile-time, or else your app won't run at all. But you can dynamically load them at runtime using LoadLibrary() and GetProcAddress() (or, if you compiler supports it, use delay-loading), which will allow you to extract the DLLs before calling their functions.
I was wondering if I can take an existing windows DLL and static link the dynamically-linked files?
I saw a number of projects to do this with Linux/elf
http://magicermine.com/
http://statifier.sourceforge.net/
http://bitwagon.com/jumpstart/jumpstart.html
I imagine this is most likely not possible, but I am running into some issues in WinPE where when I statically linked the DLLs everything started working great.
I don't have the source to the existing DLL.
I guess I could make a pass-through DLL that exposed all of the same functions and static linked?
There is no tool support for linking in the code of a DLL statically.
The problem is that a DLL is a full Windows PE executable, not a C or C++ “library” in any sense. The C++ standard has only one statement that is vaguely in support of DLL-like things (in the para about dynamic initialization after first statement of main). You’re out of luck.
But if you had the source code (as e.g. with MFC), which you say you don’t, then you could just have created static libraries.
Do note that there already is a meaning for “linking statically” a DLL, namely to have it loaded and have its functions resolved automatically.
Which is the usual way of using a DLL.
And which is in contrast to explicitly loading it dynamically and using GetProcAddress to resolve its functions.
Regarding
” when I statically linked the DLLs everything started working great
presumably earlier you have explictly loaded the DLLs dynamically, and used GetProcAddress, and presumably something about that did not work perfectly.
One main problem with GetProcAddress is that it assumes that the provided function name is encoded as Windows ANSI (the machine-dependent encoding reported by GetACP), and then (apparently) translates that to UTF-8 for the function lookup.
One workaround could be to access the function by ordinal rather than name.
One way to find the ordinal with Microsoft's tools, is to use dumpbin /exports.
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'm using Code::Blocks and hate manually linking DLLs. I found the LoadLibrary() function, and am wondering if it works like a .a or .lib file would. Does this function work like that? If not, what can I do programming-wise (if anything) to link a DLL without having to link a DLL by doing the Project < Build options < Linker settings < add < ... method?
LoadLibrary loads the requested library (and all the libraries it needs) into your process' address space. In order to access any of the code/data in that library, you need to find out the code or data address in the newly loaded region of memory. You need to use GetProcAddress.
The difference between this process and adding a library during build time is that for build-time library the compiler prepares a list of locations that refer to a given function, linker puts that list into .exe, and run-time linker loads the library, does the equivalent of GetProcAddress for the function name and places the address into all locations that the compiler marked.
When you don't have this automated support, you have to declare a pointer to function, call GetProcAddress yourself, and assign the returned value to your pointer to function. You can then call the function like any other C function (note "C" part - the above process is complicated by name mangling when you use C++, so make use of extern "C")
LoadLibrary() loads a DLL at runtime. Normaly you link when you compile the EXE, and link the DLLs like a static library at this time. If you need to load libraries dynamically at runtime, you use LoadLibrary().
For example when you implement a pluginsystem, is this usefull, as you don't know the libraries beforehand.
Not how it works at all. LoadLibrary is used to load a "at compile time unknown" DLL - such as program extensions/plugins or "This DLL for SSE, that DLL for non-SSE" based on "what can the hardware do - one could also consider having a DLL per connection type to email servers or something like that, so that the email program doesn't have to "carry" all the different variants, when only one is used for any particular email address.
Further, to use a DLL that has been loaded this way, you need to use GetProcAddress to get the address of the functions in the DLL. This is very different from linking the DLL into the project at buildtime, where functions simply appear "automagically" by help of the system loader functions that load the DLL's that are added to the project at build-time.
Contrary to static or dynamic library linking, LoadLibrary doesn't make the library's symbols directly available to your program. You need to call GetProcAddress at runtime to get a pointer to the functions you want to call.
As #Devolus mentioned, this is a good way to implement plugin systems and/or to access optional components. However, since the symbols are not available to your program in a transparent way, this is not really practical for ordinary usage.
in my Windows C++ program I have a few dependencies on DLLs (coming with drivers of input devices). I don't actually load the DLLs myself, but the drivers provide (small) .lib library that I statically link against (and I assume it is those libraries that make sure the DLLs are present in the system and loads them). I'm writing an application that can take input from a series of video cameras. At run-time, the user chooses which one to use. Currently my problem is that my routines that query whether a camera is connected already require the functionality of the camera being present on the system. I.e. let's say there is camera model A and B, the user has to install the drivers for A and B, even if he knows he just owns model B. The user has to do this, as otherwise my program won't even start (then when it started it will of course tell the user which of the two cameras are actually connected).
I'd like to know whether there is any possibility, at run-time, to determine which of the DLLs are present, and for those that aren't, somehow disable loading even the static (and, thus, dynamic) component.
So basically my problem is that you cannot do if(DLL was found){ #include "source that includes header using functions defined in lib which loads DLL"}
I think using the DELAYLOAD linker flag may provide the functionality required. It would allow linking with the .lib files but would only attempt to load the DLL if it is used:
link.exe ... /DELAYLOAD:cameraA.dll /DELAYLOAD:cameraB.dll Delayimp.lib
The code would be structured something similar to:
if (/* user selected A */)
{
// Use camera A functions, resulting in load of cameraA's DLL.
}
else
{
// Use camera B functions, resulting in load of cameraB's DLL.
}
From Linker Support for Delay-Loaded DLLs
:
Beginning with Visual C++ 6.0, when statically linking with a DLL, the
linker provides options to delay load the DLL until the program calls
a function in that DLL.
An application can delay load a DLL using the /DELAYLOAD (Delay Load Import)
linker option with a helper function (default implementation provided by
Visual C++). The helper function will load the DLL at run time by calling
LoadLibrary and GetProcAddress for you.
You should consider delay loading a DLL if:
- Your program may not call a function in the DLL.
- A function in the DLL may not get called until late in your program's
execution.
You need to load the libs at run-time. Take a look a look at LoadLibary.
This is an MSDN article about this: DLLs the Dynamic Way I just glanced over this. It's very old.
This one shows the usage of LoadLibrary: Using Run-Time Dynamic Linking