I'm trying to parallelize our build process in Visual Studio 2005 to take advantage of our multi-core hardware. Simplifying things a bit, I've got two DLLs and an application. DLL A has no dependencies. DLL B uses certain functions defined in DLL A. The application uses functions defined in both.
I thought I should be able to build A and B in parallel, because you shouldn't need to resolve symbols until you link the application. However, when I remove DLL B's project dependency on A, I get errors like the following:
YFindReplaceWidget.obj : error LNK2001: unresolved external symbol "__declspec(dllimport) public: virtual unsigned long __thiscall CORBBaseComponent::GetRefCount(void)const " (__imp_?GetRefCount#CORBBaseComponent##UBEKXZ)
Is there a way to resolve these errors so I can build these DLLs in parallel?
That's... a really weird thought pattern. DLL's are nothing but EXE's with a different extensions, they need full linking information to be built.
As long as your build is a chain like that (app->b->a), they can't be built in parallel.
Microsoft officially introduced a multiprocessor built option in VS2008. It will allow the build to start multiple compilers for the same project. The easy solution is just upgrade to the latest version of Visual Studio.
If you are stuck on VS2005, then it is actually available there as well, but not officially supported. Just add /MP as an additional compiler option.
http://blog.280z28.org/archives/2007/10/17/ (Advices you NOT to use it on your buildserver)
http://msdn.microsoft.com/en-us/library/bb385193.aspx
Related
I am trying to implement lua into C++ however I am having problems with Visual Studio saying that I have an unresolved external symbol called "_sprintf", "_fprintf", and "__iob_func".
I'm pretty sure that these functions exist in C++ since I have seen (well the first 2) them used before.
You're probably running into the C-runtime changes introduced in VS2015: The Great C Runtime Refactoring.
You can add the following library to supply those definitions in the Additional Dependencies in the Project Settings -> Linker -> Input:
legacy_stdio_definitions.lib
I am adding .dll to C++ project.
IDE: Visual Studio 2013
What I did:
Added directory with headers to VC++ Directories -> Include Directories
. It's ok, I can include headers, IntellySense sees names
in these files.
Added .lib file to Additional Dependencies section and a path to this
file in both VC++ Directories -> Library Directories and Linker -> General -> Additional Library Directories.
Placed actual .dll file to DEBUG folder (also to project folder, just
to be sure)
Used dumpbin.exe to get sure I have exported all needed classes in my
.dll
And I still get a bunch of unresolved externals with functions stored in that .dll. Any suggestions?
I found this question and set Use library Dependency Inputs to Yes. Still no luck.
Some more info:
Error example:
Error 2 error LNK2019: unresolved external symbol "__declspec(dllimport) public: double __thiscall Fem::Node::GetX(void)" (__imp_?GetX#Node#Fem##QAENXZ) referenced in...
This function in dumpbin output:
172 AB 000F81A0 ?GetX#Node#Fem##QEAANXZ
I see some difference in the last part of the name. Somehow, as I mentioned in the comments, I got it working in Qt project with Visual Studio compiler.
This is usually a bad idea, since it doesn't lead to a reusable library. The application can't be rebuilt with a new compiler or even new compile settings without also rebuilding the DLL. It is safer to just compile the classes you use in statically. That said, there are some benefits if used in conjunction with delay-loading, so...
In order to store a class implementation in a DLL, while building the DLL you must use __declspec(dllexport) on the class, and when consuming it there must be __declspec(dllimport). Import libraries have shims to forward free function references to DLLs but those don't work for classes and class members.
Usually macros are used to accomplish the switch between dllexport and dllimport.
Now that you've shown mangled names, the difference becomes apparent, and demangling gives a clue to where the problem came from.
Linker is looking for
public: double __thiscall Fem::Node::GetX(void)
But DLL is exporting
public: double __cdecl Fem::Node::GetX(void) __ptr64
Notice that the calling conventions are different; if this had linked, you would have crashed as soon as you tried to call this function.
You cannot use exports from a DLL that have C++ signatures from an application compiled differently. Are you mixing architectures (x86 vs x86_64 vs ARM)? Can't do that either, not even using highly-compatible C calling signatures.
I recently got assigned to a c++ project, although I am not a c++ developer. I was provided Visual Studio 2010 Professional as IDE. So I gave it a shot.
I am to write a c++ dynamic library (*.dll) which wraps two static libraries (*.lib). The static libraries are third party libraries we bought a couple of years ago from another company. Using the dumpbin /header ... cmd call, I can say that both static libraries have the following file header value:
14C machine (x86)
I got this task working for the Win32 solution platform. I added the header files and the libraries to the project. The libraries are included by writing two #pragma comment(lib, ...) statements within the .cpp I need the functions in. Works like a charm. A sample function looks like this:
extern "C" void OURFreeStringBuf(Cm_StringBuf *sbuf)
{
FreeStringBuf(sbuf); // the call to the static library
}
This dynamic library is to be used in x64 architectures, aswell. So I tried to set the solution platform to x64. Now I get the following error for each call of one of the static libraries' functions (no code changes or other configuration changes were made):
error LNK2001: unresolved external symbol "..."
followed by a summarizing error:
error LNK1120: 29 unresolved external links
Could these errors be the result of trying to link x86 lib files in a x64 dll? Is there any chance to complete this task using the provided static libraries?
Thank you very much in advance.
You can not - in other words, there is NO WAY to - link a 32-bit library with a 64-bit executable or DLL (or a 32-bit executable to a 64-bit DLL or vice versa). You will either have to compile your .DLL/.EXE as 32-bit, or find a 64-bit version of the 32-bit library. No other solution!
The 64-bit architecture is different from the 32-bit architecture in several aspects, but most importantly, the addresses (pointers) are 64-bit in a 64-bit architecture, which prevents almost any 32-bit code from working correctly in a 64-bit environment (because the upper 32 bits of the addresses are lost, which doesn't produce anything meaningful).
I'm working on a cross-platform c++/qt project with a plugin system, we are using so files on linux and dll on windows. We are using gcc on Linux and Visual Studio 2010 on Windows through cmake.
The problem is our plugins sometimes need to call a function from the application source code, which is working fine on Linux with gcc by just including the header files. But on Visual Studio, we got unresolved external symbol errors.
Is it because so and dll files works differently?
thank you.
The default behaviour for exporting symbols from dlls on Windows is exactly opposite: by default, symbols are invisible, you need to export them explicitly. With VC++ this is done by __declspec(dllexport) declarators.
EDIT (Information added): You are entering a region of non-standardized, system specific behaviour... There are much more problems associated with writing cross-platform "pluggable" component systems in C++ than you might be expecting. On Windows there are so called import libraries, which define all symbols exported from a dll. You have to link against these libraries in order to resolve these symbols. This is called implicit linking. You can also link explicitly which means loading dll and its exported symbols at run-time. However all these are just technical details compared to so called binary compatibility issues, which will almost certainly kill you, if not considered during the design of your component system.
I am wondering about one thing: You said you're using Qt. Qt application framework has got it's own cross platform conventions and rules for writing and building pluggable components. Why don't you stick with these...?
Problem:
I'm trying to use a library named DCMTK which used some other external libraries ( zlib, libtiff, libpng, libxml2, libiconv ). I've downloaded these external libraries (*.LIB & *.h files ) from the same website. Now, when I compile the DCMTK library I'm getting link errors (793 errors) like this:
Error 2 error LNK2005: __encode_pointer already defined in MSVCRTD.lib(MSVCR90D.dll) LIBCMTD.lib dcmmkdir
Error 3 error LNK2005: __decode_pointer already defined in MSVCRTD.lib(MSVCR90D.dll) LIBCMTD.lib dcmmkdir
Error 4 error LNK2005: __CrtSetCheckCount already defined in MSVCRTD.lib(MSVCR90D.dll) LIBCMTD.lib dcmmkdir
Error 5 error LNK2005: __invoke_watson already defined in MSVCRTD.lib(MSVCR90D.dll) LIBCMTD.lib dcmmkdir
Error 6 error LNK2005: __errno already defined in MSVCRTD.lib(MSVCR90D.dll) LIBCMTD.lib dcmmkdir
Error 7 error LNK2005: __configthreadlocale already defined in MSVCRTD.lib(MSVCR90D.dll) LIBCMTD.lib dcmmkdir
Error 8 error LNK2005: _exit already defined in MSVCRTD.lib(MSVCR90D.dll) LIBCMTD.lib dcmmkdir
Documentation:
This seems to be a popular error for this library so, they do have a FAQ entry addressing this issue which ( http://forum.dcmtk.org/viewtopic.php?t=35 ) says:
The problem is that the linker tries to combine different,
incompatible versions of the Visual
C++ runtime library into a single
binary.
This happens when not all parts of your project and the libraries you
link against are generated with the
same code generation options in Visual
C++.
Do not use the /NODEFAULTLIB workaround, because strange software
crashes may follow. Fix the problem!
DCMTK is by default compiled with the "Multithreaded" or "Multithreaded
Debug" code generation option (the
latter for Debug mode).
Either change the project settings of all of your code to use these code
generation options,
or change the code generation for all DCMTK modules and re-compile.
MFC users beware: DCMTK should be compiled with "Multithreaded DLL" or
"Multithreaded DLL Debug" settings if
you want to link the libraries into an
MFC application.
Solution to same problem for others:
Huge Amount of Linker Issues with Release Build Only says:
It seems that your release build is
trying to link to something that was
built debug. You probably have a
broken dependency in your build, (or
you missed rebuilding something to
release by hand if your project is
normally built in pieces).
More technically, you seem to be
linking projects built with different
C Run Time library settings, one
with "Multi-Threaded", another one
with "Multi-Threaded Debug". Adjust
the settings for all the projects to
use the very same flavour of the
library and the issue should go away
Questions:
Till now I used to think that Name mangling is the only problem that may cause linking failures if its not been standardized. Just now I knew there are other things also which can cause same effect.
Whats up with the "Debug Mode" (Multi-Threaded Debug) and "Release Mode" (Multi-Threaded)? What exactly is happening under the hood? Why exactly this thing is causing linking error?
I wonder if there is something called "Single-Threaded Debug" and "Single-Threaded" which again causes the same thing.
Documentation talks something about "Code Generation Options". What Code Generation Options? WTH are they?
Documentation specifically warns us not to use /NODEFAULTLIB workaround. (example /NODEFAULTLIB :msvcrt ). Why? How would I cause troubles? what exactly is it?
Please explain the last point in the documentation for MFC users. Because I'm going to use MFC later in this project. Explain Why should we do it? What troubles would it cause if I don't.
Anything more you'd like to mention? I mean regarding similar errors. I'm very interested in Linker & its problems. So, if there are any similar things you can mentions them or some keywords atleast.
Whats up with the "Debug Mode"
(Multi-Threaded Debug) and "Release
Mode" (Multi-Threaded)? What exactly
is happening under the hood? Why
exactly this thing is causing linking
error?
The linker drags in libraries for several different reasons. The simplest is that a library is listed on the linker command line, or in the linker answer file on the linker command line. But any object files, whether compiled in your project or packed into a library, can also contain linker options including requesting particular libraries be linked in. In fact, the Visual C++ compiler automatically embeds such linker options matching the project options you use when compiling.
At link time, all the linker options from all object files and objects in static library files get combined. If more than one CRT library filename is requested, the linker reads in all of them and them you get naming conflicts, where the linker doesn't know which one to use.
I wonder if there is something called
"Single-Threaded Debug" and
"Single-Threaded" which again causes
the same thing.
There used to be, but the last few versions of Visual C++ have only shipped multi-thread compatible libraries.
Documentation talks something about
"Code Generation Options". What Code
Generation Options? WTH are they?
Look inside your project options.
Documentation specifically warns us
not to use /NODEFAULTLIB workaround.
(example /NODEFAULTLIB :msvcrt ). Why?
How would I cause troubles? what
exactly is it?
If you use /NODEFAULTLIB, all the linker settings stored within object files and objects in libraries get ignored. You'll end up with no runtime library and maybe missing other libraries. You can add them back in by hand, but it's still a big mess.
Please explain the last point in the
documentation for MFC users. Because
I'm going to use MFC later in this
project. Explain Why should we do it?
What troubles would it cause if I
don't. Anything more you'd like to
mention? I mean regarding similar
errors. I'm very interested in Linker
& its problems. So, if there are any
similar things you can mentions them
or some keywords atleast.
MFC applications and the MFC library have to use the same memory management functions, so that memory allocated by MFC can be freed by the application and vice-versa. FILE handles and other resources are also shared. The MFC DLLs are already compiled to use the CRT in a DLL, and in order to be able to share resources you need to use the same CRT, which means using a DLL too.
You need to configure project properties so that your debug build links with DCMTK's debug build and your release build links with DCMTK's release build.
The above is what you need to do. Below are explanations of some other random things you asked about.
Older versions of Visual Studio used to have single threaded libraries (release and debug versions) besides multithreaded libraries (release and debug versions). For your project you can pretend single threaded libraries never existed.
If you experiment with random ways to trick the linker into shutting up and leaving problems to be found by your customers instead of by yourself, you might find that the /NODEFAULTLIB option will do that. The makers of the DCMTK library are warning you not to do that because some other people did the same dumb thing in the past.
Whats up with the "Debug Mode" (Multi-Threaded Debug) and "Release Mode" (Multi-Threaded)? What exactly is happening under the hood? Why exactly this thing is causing linking error?
They are different versions of the C runtime library. You can statically link to the runtime library in debug and release mode. In the Code Generation Options (mentioned below), those would be "Multi-Threaded Debug" and "Multi-Threaded". The options "Multi-Threaded Debug DLL" and "Multi-Threaded DLL" dynamically link to the C runtime. By dynamically linking to the runtime, you'll also have to ship your installer configured to install the VC redistributable package that contains the proper runtime dlls for your version of Visual C++.
Statically linking to the C runtime is generally frowned upon, even by Microsoft:
In addition to all the methods
described above of distributing the
Visual C++ libraries DLLs, there is
one last option for building your
application which does not require you
to distribute the DLLs. However, this
option only works for native-only code
(it is not supported with /clr) and
leaves your customers seriously
vulnerable to any security holes as
well as adds a significant burden upon
yourself to patch all customer systems
should a vulnerability be found in any
of the libraries. This option is to
statically link in the libraries as
.lib files instead of dynamically
loading them as DLLs. You do this by
using the /MT flag on the cl.exe
command line (vs /MD), or selecting
the appropriate option in your project
properties through Visual Studio. You
may wish to use this option when
testing early debug builds of your
application on test machines before
you start working on setup. [See
footnote 3]
However, I can think of no scenarios
in which this is actually the right
thing to do when shipping your product
to customers. Basically, what this
approach does is pulls in the binary
code needed from .LIB files at compile
time, making it a part of your .exe or
.dll files. It increases the size of
your application, and there is no way
to update the libraries apart from
recompiling your application with new
.LIBs and redistributing your
application all over again. What this
means is that unless you go touch
every single machine which has
installed your application every time
there is a security vulnerability
found in the Visual C++ libraries and
completely reinstall your updated
binaries, you will be leaving your
customers vulnerable to attack. If
instead you use the DLLs, every time
there is a security vulnerability
found in the Visual C++ libraries,
Microsoft will install the update
centrally into the WinSxS folder via
Windows Update and all requests for
the DLLs will be redirected to the
updated version. This removes all
servicing burden on your side and also
allows the user to install one small
update which will touch all their
applications instead of replacing
every installed exe and DLL on their
system. Please, do not distribute an
application built by linking
statically against the Visual C++
libraries unless you have a system in
place for updating every customer
machine and also have a very good
reason to do so. At this time, I can
think of no circumstance under which
this would be the right thing to do
for a shipping application.
I wonder if there is something called
"Single-Threaded Debug" and
"Single-Threaded" which again causes
the same thing.
No such thing, see above.
Documentation talks something about "Code Generation Options". What Code Generation Options? WTH are they?
Right click on your Visual C++ project (from within Visual Studio) and select Properties. Under Configuration Properties->C/C++->Code Generation
Documentation specifically warns us not to use /NODEFAULTLIB workaround. (example /NODEFAULTLIB :msvcrt ). Why? How would I cause troubles? what exactly is it?
Take their advice and don't do it.
Please explain the last point in the documentation for MFC users. Because I'm going to use MFC later in this project. Explain Why should we do it? What troubles would it cause if I don't.
Because MFC is dynamically linked to the C runtime, using libraries that are statically linked to the C runtime will cause the linker errors you listed first in your post.
Anything more you'd like to mention? I mean regarding similar errors. I'm very interested in Linker & its problems. So, if there are any similar things you can mentions them or some keywords atleast.
From my experience, always dynamically link to the C runtime. It generally saves you a lot of headaches like the one you're experiencing right now.