I am working with Visual Studio and I am trying to get into dlls. I'm wondering how the linker knows where to find a DLL just from the lib file alone.
I specify the lib file and its location in the project settings but where isthe location of the associated dll file specified?
Or maybe i don't understand the topic correctly.
The Standard Search Order for Desktop Applications from the Microsoft Dll Search Order documentation:
If SafeDllSearchMode is enabled, the search order is as follows:
The directory from which the application loaded.
The system directory. Use the GetSystemDirectory function to get the path of this directory.
The 16-bit system directory. There is no function that obtains the path of this directory, but it is searched.
The Windows directory. Use the GetWindowsDirectory function to get the path of this directory.
The current directory.
The directories that are listed in the PATH environment variable. Note that this does not include the per-application path specified by the App Paths registry key. The App Paths key is not used when computing the DLL search path.
If SafeDllSearchMode is disabled, the search order is as follows:
The directory from which the application loaded.
The current directory.
The system directory. Use the GetSystemDirectory function to get the path of this directory.
The 16-bit system directory. There is no function that obtains the path of this directory, but it is searched.
The Windows directory. Use the GetWindowsDirectory function to get the path of this directory.
The directories that are listed in the PATH environment variable. Note that this does not include the per-application path specified by the App Paths registry key. The App Paths key is not used when computing the DLL search path.
Related
I'm trying to set up SDL2 in C++ Visual Studio but when I run the code(just some starter code I copied) it pops up with an error box box that talks about "SDL2.dll cannot be found" I tried switching to x64 but that was no help. I can see that the dll is right next to the lib files but it just won't work.
Your problem is the lib folder is not a place that your OS will search for dependent dlls by default. To fix this you would have to help your OS find the dll. There are several methods you can use to tell your OS where to look. One is adding an entry to your PATH environment variable that contains the full path to the folder containing the dll.
This site can help with setting the PATH: https://www.computerhope.com/issues/ch000549.htm
As second method is to put the dll in the same folder as the executable.
By default your OS probably is using the safe search option described here:
The directory from which the application loaded.
The system directory. Use the GetSystemDirectory function to get the path of this directory.
The 16-bit system directory. There is no function that obtains the path of this directory, but it is searched.
The Windows directory. Use the GetWindowsDirectory function to get the path of this directory.
The current directory.
The directories that are listed in the PATH environment variable. Note that this does not include the per-application path specified by the App Paths registry key. The App Paths key is not used when computing the DLL search path.***
I have a dll in my project which I am referring through absolute path(C:\test\something\abc.dll) to load in my project. How do load it relatively or is there is better way to include it in visual studio project?
MSDN::
Before the system searches for a DLL, it checks the following:
If a DLL with the same module name is already loaded in memory, the system
uses the loaded DLL, no matter which directory it is in. The system
does not search for the DLL.
If the DLL is on the list of known DLLs
for the version of Windows on which the application is running, the
system uses its copy of the known DLL (and the known DLL's dependent
DLLs, if any). The system does not search for the DLL. For a list of
known DLLs on the current system, see the following registry key:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session
Manager\KnownDLLs.
The standard searching order for Dlls is::
The directory from which the application loaded.
The current directory.
The system directory.
The 16-bit system directory. There is no function that obtains the path of this directory, but it is searched.
The Windows directory.
The directories that are listed in the PATH environment variable.
You can always have your Dll with the application in the same directory. Carrying it as resource within application is not advisable.
You can specify dll name without path and place the dll in the same directory where the executable loading it resides, or in the current directory (the one from which you launch the program).
I have four different .exes in differend subdirs of one specific directory. All of the programs need the exact same .dlls (Qt5Core, Qt5Gui and Qt5Widgets). Is there a way of having theese three .dlls just in the root directory insted of having to copy them into each subdirectory?
Here you find the order in which DLL paths are searched on Windows:
Since Safe DLL search mode is enabled by default, the order is
The directory from which the application loaded.
The system directory. Use the GetSystemDirectory function to get the path of this directory.
The 16-bit system directory. There is no function that obtains the path of this directory, but it is searched.
The Windows directory. Use the GetWindowsDirectory function to get the path of this directory.
The current directory.
The directories that are listed in the PATH environment variable. Note that this does not include the per-application path specified by the App Paths registry key. The App Paths key is not used when computing the DLL search path.
So the easiest thing to do is to ensure that you run your app from the working directory where you put the DLLs (5.). That could be done by writing a starter .bat file that navigates there first and then runs the application relative to the DLL direcory.
The other way would be to add the DLL directory to PATH in a starter .bat file (6.).
In both cases you need a wrapper script for each .exe that you want to run.
You could avoid that if you can make sure that links to the application set the working directory properly. This would work if you have an installer creating the shortcuts for the user and you know the user will not create one himself by just right-clicking the .exe.
There might also be a way using hardlinks or junctions but I don't know if you can copy and deploy those like symbolic links on Linux or if you need to create them on the target system.
Yes, you are using Windows and you can add your root directory as a path in Environment Varibles from
Computer-> Properties->Advanced System Settings -> Environment Variables
I have a third party library (say, tp.lib) and the third party dll (say, tp.dll) which I need to use in my C++ project (my project makes a dll, lets call it my.dll).
I have included the library with the #pragma comment(lib, "libraryname") in the header file
and also included the path of the library file in the configurationproperties->linker->additional library directories in my C++ Visual Studio project.
The code compiles and links okay. but fails to execute. When I used depends to check if i am missing something, I observed that the tp.dll is not found. The tp.dll resides in the same library folder where the tp.lib resides.
What should I do so that tp.dll gets included to my.dll?
DLLs have a different search path. Quote below from docs:
With both implicit and explicit linking, Windows first searches for "known DLLs", such as Kernel32.dll and User32.dll. Windows then searches for the DLLs in the following sequence:
The directory where the executable module for the current process is located.
The current directory.
The Windows system directory. The GetSystemDirectory function retrieves the path of this directory.
The Windows directory. The GetWindowsDirectory function retrieves the path of this directory.
The directories listed in the PATH environment variable.
Note
The LIBPATH environment variable is not used.
The search path at runtime does not include the folder where you put the lib library, so putting the DLL with the lib is not enabling the OS to find it at runtime. You can add that to the path, or move the DLL. The list of search precedence is on MSDN.
You can't "include the dll into another dll". You need to either deploy them together, or put the dependency dll in a place where Windows will find it.
In a Project of mine, I use a Delphi Application which dynamically loads a wrapper DLL (exporting C-Style functions) which in turn is statically link against a bunch of 3rd party DLLs.
It works fine on my test machines, but on my customers computer it failed to initialize with an error Message like "Couldn't find entrypoint _somefunction#4AKKZ in TMYlibrary.dll".
After some investigation with sysinternal's process monitor, I realized that Windows would look fror DLLs in windows/sytem32 first, so if a DLL named similar to my DLL was present in system32, windows would pick that one and try to find my function entry points in it - which would fail.
Do you know of a possiblity to change windows' DLL the searching behaviour?
Additional Information
[Update] The .exe file is located on the top level of the application's folder tree.
The Wrapper and the 3rd-party-DLLs ar e both located in the Subfolder /bin of my apps Folder
Dev platform is windows XP/7, using VS2008 for the dlll and Delphi 2010 for the application
I found another solution myself:
SetDllDirectory adds an additional search path to the list of locations to look at.
From http://msdn.microsoft.com/en-us/library/ms686203%28v=VS.85%29.aspx
After calling SetDllDirectory, the DLL search path is:
The directory from which the application loaded.
The directory specified by the lpPathName parameter.
The system directory. Use the GetSystemDirectory function to get the
path of this directory. The name of
this directory is System32.
The 16-bit system directory. There is no function that obtains the
path of this directory, but it is
searched. The name of this directory
is System.
The Windows directory. Use the GetWindowsDirectory function to get
the path of this directory.
The directories that are listed in the PATH environment variable.
(maybe i should do my googling before I post on SO ;)
Ship the DLL in your program's folder. (same as the exe file).
Then Windows should try your version first.