I ran into a strange problem with a Visual Studio 2008 project I was working with recently.
I am trying to compile a new static library that uses functions from another static library. (Let's say Lib1 is my static library project, and Lib2 is the lib file that Lib1 depends on).
I am able to build lib1 without issue; It includes the header files for lib2 and calls its functions, and there are no problems.
The problem is when I build a separate test project that has Lib1 as a dependency; it won't build and I get linker errors. The unresolved externals are the functions I am trying to call within Lib1 that are from Lib2.
This is all fixed when I include Lib2 in my test project as well.
This all makes sense to me of course; I can test that Lib2 is not being built into Lib1..
My question is: is there a way to do this? I would ideally like to be able to deploy Lib1 as a standalone lib without requiring Lib2. (Lib2 is actually just a Lib from the Windows Platform SDK, so it's not really a big deal...)
Is this not allowed because it would allow people to "hide" third party libraries in their own, or something?
What would be a professional approach to this problem?
Thanks!
--R
I would not advise using a librarian to take Windows' library contents into your own library -- it's likely that that's against the license.
I see two possibilities
Documenting the dependency
Using a #pragma in your .h file that requests the .lib to be linked against. If VS can find it, it's the same as including it on your link line.
http://msdn.microsoft.com/en-us/library/7f0aews7(VS.80).aspx
#pragma comment(lib, "libname.lib")
You need to use a tool called a librarian to do this. A librarian allows you to create and modify library (.lib) files. In visual studio check under the Librarian section of your project properties. A command line version also comes with visual studio (lib.exe).
Just document the dependencies of your lib.
As long as the library you depend on is available to anyone that could use your library, this is the preferred solution. Especially considering that the library user could also depend on this platform SDK lib - if you had it embedded then he'd get funny linker errors with multiply defined symbols.
This is a fairly normal problem - you wouldn't normally attempt to include 'lib2' into 'lib1' but simply document that it's required to be linked against in order to work. There is nothing wrong with declaring the use of other libraries (apart from any licensing issues of course) so you are already doing the right thing.
If you really want to do this, you can extract the .obj files from Lib2 and add them to Lib1.
See How to Extract .OBJ Routines from .LIB Files Using LIB.EXE -- I hope it is still relevant for VS2008.
Instead of simply documenting your dependencies, use #pragma comment(lib, 'lib2name') in your code to make the linker pull in the other library automatically. Since you said you're using a standard library that comes with the SDK, this should eliminate all burden on the application.
Related
I have some confusion about static and dynamic linked libraries and .lib and .dll files.
I have a project with two libraries, one I built myself and one is from an open source library.
The one I built myself is a separate project in the same solution (Visual Studio 2015, C++), and I don't need to copy over the .lib files or create a DLL for the executable to build and run
For the other open source library, I do need to copy over the .lib file and the DLL into the executable folder. However, I thought it would be possible to statically link a .lib file and not have to copy over the DLL.
Does this mean I need to compile the Open Source library differently? Like change the define __declspec(dllexport) to __declspec(dllimport) ? Or change /mD to /mT in compiler options?
I tried both of these, but it's still saying that it can't start without the .dll
Or can I get away with changing a setting in the executable project to link this library statically? If so, what are these settings?
EDIT: I know this is a standard question that can be looked up on google, but I haven't been able to find an exact answer for a while. Mainly, I'm confused about what settings need to be changed, and which project they need to be changed in. (The library or the executable).
I'm under assumption that static linking means the library is built into the executable, and dynamic linking means the library needs to be in a separate file, if this is incorrect, please let me know. Otherwise, I need to know how to build the library into the executable file.
And I can go ahead and change the build options in the open source library, and I tried this already.
Thanks,
-D
In Windows, dll files (dynamically linked libraries) need to be in the same directory as the application or on the search path. lib files (static libraries) need to be statically linked during linking (the last step of building the application). It's common in Windows so have a library come with both a dll and lib file. In this case, the lib file is an import library containing the information needed to easily link to the dll.
Place the dll file where your application will be built and statically link with the lib file. Go to 'Project->Properties->Link->Input->Additional Dependencies' and 'Project->Properties->Link->General->Additional Library Directories' to specify the static libraries you want to link.
Edit: It seems I misunderstood the question. The question is how to recompile a dynamic library as a static library. You need the source code of the library you are using along with it's Visual Studio Project file. Open the library and in `Project->Properties->General->Configuration Type' change it from Dynamic Library to Static Library.
Beware that Dynamic Library uses the Linker group of properties while the Static Library uses the Librarian group of properties. Changing between these types may cause the project to drop essential linker flags options. Since every library is different, I can't predict what you will have to do work around this. Make sure to backup the project file so you can see the original options and flags.
I had to change the setting for "Static Library" for All Configurations, not just Debug, although it was building in Debug. Not sure what may have caused this. Possibly because the debug and release builds for the library were set to the same folder, it may have been overwriting the debug builds with release builds when building
I've been using Boost's ASIO library to do network and socket communication. Now I'm getting to a point in the development cycle where I'd like to clean things up and make them a little more modular. My first thought was that I would use a separate project for just the network communication part (essentially factoring out the Boost-dependent stuff) and use one visual studio project in two different visual studio solutions. Something like:
Client.sln
-> Client.vcxproj
-> Networking.vcxproj
Server.sln
-> Server.vcxproj
-> Networking.vcxproj
I tried to do this, but I have the problem that my Networking.vcxproj has turned into a header-only project due to the fact that I'm creating nothing but template classes. What I would ideally like to do is place the references to the boost pre-compiled libs only in the Networking.vcxproj and link against the output of Networking.vcxproj. However, if I understand correctly, there's nothing to link against since my Networking.vcxproj has no .cpp files.
Is there any way to link against my Networking project and the boost ASIO libs without specifying all the additional library dependencies in all the projects? i.e. Is there any way to somehow create the project settings so that I don't have to duplicate the boost library dependencies every time I create a new application which uses the Networking.vcxproj project?
Try to put
#pragma comment(lib, "libname.lib")
in one of your networking header files. This should force any project that include that header to link against the specified library (with name "libname").
See
pragma comment
We have a large project using VS2008 and boost 1_42. I'm trying to upgrade to VS2010 and boost 1_44. I installed VS2010 and boost 1_44 and converted the project. Now I am trying to build, and everything compiles, but fails when linking:
LINK : fatal error LNK1104: cannot open file 'libboost_thread-vc90-mt-1_42.lib'
I have changed the include and lib directories to point to the new boost 1_44 files and I have renamed the old boost 1_42 directory.
Why is the linker still looking for a vc90-1_42 file, when it is only using 1_44 headers? Is there a way that I can determine WHY the linker wants this file? The linker obviously thinks it needs the file, but why?
I have cleaned the project and I am re-building to ensure any old build files are erased.
I've run into exactly this problem a couple of times too. It's usually been some old temporary files but like in your case cleaning didn't always do the trick straight away. Does your project include any static libs that might have been built with 1.42?
Something you can try which may or may not be helpful in tracking down your issue:
Rename the old boost directory back to it's original name
Clean the solution
Under C/C++->Command Line->Additional Options add "/showIncludes"
Under Linker->Command Line->Additional Options add "/verbose:lib"
Rebuild all
Then when you build you'll be able to see at which point 1.42 headers are included, etc. in the output window. Somehow doing this helped me in tracking down where the problem was.
Along with changing the lib directory, you need to change the name of the boost library. That's in the Linker | Input section of the project settings.
Your added comment makes it clear that the dependency on the Boost 1.42 library was being created indirectly by another library that hadn't been rebuilt.
For this you basically have two choices: either add that library as a project to your main solution, and make sure it has enough dependency information that it'll be re-built when you upgrade Boost, or use the /Zl compiler switch when you build your library. This tells the compiler you're building a library so you do not want to embed library dependencies like this.
Boost uses
#pragma comment(lib)
command to inform the linker of libraries it needs to link with. It is not an error. If Boost says you need it, it's likely you do.
On How can I find out why the linker wants this file?
There are programs which will go through your app and dlls/libs and report the content of manifests and what the binaries report they depend on. You could then scan the report for the unexpected libraries being included. We used this mainly to find libs including the previous version of the VC runtime.
Have not used the one we had in about 5 years though, now if only I could remember the name of the app!
DependancyWalker (depends.exe) will allow you to see dependancies of dll/exe but not static libs.
You could open each binary as a 'file' in MSVS and look at the manifest content by hand, but I imaging this would be a bit painful. I've not tried this with a static lib.
I'm new to C++ and there's something I just completely don't get. In C#, if I want to use an external library, log4net for example, I just add a reference to the log4net DLL and its members are automatically available to me (and in IntelliSense). How do I do that in non-managed C++?
Often, the library comes with 1) a header file (.h) and 2) a .lib file in addition to the .dll.
The header file is #include'ed in your code, to give you access to the type and function declarations in the library.
The .lib is linked into your application (project properties -> linker -> input, additional dependencies).
The .lib file usually contains simple stubs that automatically load the dll and forward function calls to it.
If you don't have a .lib file, you'll instead have to use the LoadLibrary function to dynamically load the DLL.
The basic concept is the following:
There are 2 types of libraries: static & dynamic. The difference between them is that static libraries, during the linking build step, embed their compiled code in your executable (or dll); dynamic libs just embed pointers to the functions and instructions that some dll should be loaded when program is going to be loaded. This is realized for you by the linker.
Now you can decide which of those two you are going to use. DLLs have many advantages and disadvantages. If developing a huge application it might be worthy to consider using DLLs with delay loading instead of static lib's. Some libs are simply delivered to you as DLLs and you have no choice. Anyway the easiest way for a beginner would be to use static libraries. That would make your deployment and test much easier, since, when dealing with DLL you have to ensure that they are found at runtime (even when using debugger), this involves either copying everything in one directory or dealing with path variables.
Usually a DLL provider (if it is intended that you should be able to deal with the library) delivers you a header file(s) and a .lib which contains the calls into the desired DLL. Some vendors (e.g. boost) only require you to include the header file and the lib is automatically linked to your executable (can be achieved through compiler prorietary pragma directive). If it is not the case you must go into the project settings of the C++ project (project properties/Configuration Properties/Linker/Input) and enter the lib file name into the "Additional Dependencies" row, e.g. iced.lib; iceutild.lib. You can also put fully qualified path names there. Be aware that you have to enter the lib file names for both configurations (Debug, Release). This is the procedure you do with static libraries and Dll equally. The only difference that DLL will require a DLL lib to be either in you app-directory or in one of the path-directories.
After that step, you still might get compiler errors if you try to link incompatible libraries. There are many reasons, why they can be incompatible. But try to first link the lib this way and see if works. If not, post again your errors here ;)
Include file(s) is(are) used to be included in places, where you would like to use smth. from the lib. Just include it and the compiler will know that the symbols must come either from another (compiled) compilation unit (compiled cpp-file=>object file) or the .lib. It will make the look up and notify you if the required symbols are not found.
Good Luck,
Ovanes
P.S. This might be hard in the beginning, but when you get used to it, it will be easy.
C++ doesn't have libraries in the sense you're thinking of. It has header files that you #include, and it has things called libraries that the linker deals with, which contain the compiled code. You need to add the libraries (.LIB files) to the linker settings.
On Windows if you're using a DLL, ideally you should have a .LIB file to go with it that is called the Import Library for the DLL, and you add that .LIB file to your linker settings.
The first thing you need to do is to #include the header file that describes the functions that are available in that library.
The actual code for the library will be in one of 2 places:
A static library (.lib)
A dll (.dll)
Depending on how the library's code is given to you (as .lib files, or as a .dll), you'll have to either:
#pragma comment( lib, "libraryname.lib" ) if its a .lib
LoadLibrary if its a .dll
Sometimes a package comes with BOTH a .lib file that you need to link to, and a .dll file. In this case you don't need to call LoadLibrary, you only need to #pragma comment( lib, "libaryfile.lib" ) because in this case the .lib links you into the .dll.
A very important detail is to put the DLL where your application can find it. Charles Petzold says:
When Windows needs to load a DLL module before running a program that requires it, the library file must be stored in the directory containing the .EXE program, the current directory, the Windows system directory, the Windows directory, or a directory accessible through the PATH string in the MS-DOS environment. (The directories are searched in that order.)
Programming windows, 5th ed
MSDN
I don't recommend using the project properties menu to link because it isn't as visible what libraries you're linking to.
See also
It's pretty easy to use a library in VC++ 2008 if you create a project for it and build it alongside the other projects in your solution, but what if the library has too complex of a build process and must be compiled separately via makefile?
My library is like that, and while I've had no problem compiling it on the command line, I have no clue what to do with the resulting header files and .lib file. I've put them all in one directory and added its path to my main project's Additional Include Directories, so it finds the header files just fine. I've also added the relevant info to Additional Library Directories and Additional Dependencies.
Perhaps there's another setting I'm forgetting to set besides these three? I'd appreciate all the help I can get. Thanks.
EDIT Here are the syntax errors I'm getting:
http://pastebin.com/m72ece684
Okay, based on those errors, it has nothing to do with finding your .lib files, it's choking on the header files.
Edit:
It looks like somewhere in windows.h, there is a macro definition for X942_DH_PARAMETERS which is breaking your dl_group.h.
Instead of putting your botan headers at top, but windows.h at top, and then right before you #include the botan headers add this line:
#undef X942_DH_PARAMETERS
Or as I just discovered, that macro is defined in wincrypt.h, and if you add NOCRYPT to your preprocessor definitions it won't include that file. Since you're using a third party crypto library you probably don't need wincrypt.
While I can't exactly say what your problem is I can offer some advice as to how to find a solution. I suggest creating a simple library that contains a single method and a single class, build it, and then try to successfully link it to your project. Once you get that done on a smaller scale, try repeating the steps with your original library.
For msvc compiler you can add
#pragma comment(lib, "MYLIBNAME.lib")
in your header. This will automatically make the linker look for "MYLIBNAME.lib" in the "Additional Library Directories".
If no longer an error occures
Can't find header ...
Can't find MYLIBNAME.lib
the problem is probably related to some other stuff like wrong C runtime, debug release mismatch, ...
P.S.: If the lib is in the solution tree just setting the dependency on the lib, will cause VS to add the targetpath to the libfolder and the libname to the libraries.