I'm working with Embarcadero XE8 C++ builder 32 bit.
I was adding a library to my program for solving the Unresolved external error.
When I added the library I got the error as in the title. So I searched the web and found this topic on stackoverflow:
Linker error "contains invalid OMF record"
As it says the COFF2OMF tool, CAN work. Sadly it didn't work for me, I give a 7mb library file, when I convert it with the tool it's only 41kb... so I guess the convertion failed. When I add the converted files to my program it just ignores it and still says the unresolved external error.
So how can I get my library working with my C++ builder?
A little background:
Libraries need to be compiled with the same kind of tool as the application you are trying to make, because every compiler does things a wee bit differently. Most libraries for Windows are compiled with the MVSC (Microsoft Visual Studio Compiler).
You're using the Embarcardero Compiler, which means that the MVSC libraries are incompatible (you may have noticed that ;)).
You have multiple options.
If you can, get the source of the library and compile it with your own compiler. That way the chance to succeed is the highest.
I may be mistaken since it's been a while, however I believe there's a tool called implib which takes the shared library (.dll) and generates an Embarcardero-style .lib from that for use in your project.
Use COFF2OMF to convert the static library. And even if the file size is strange, do at least try it.
Try the LoadLibrary function call. This one requires you to map the functions you need manually, however you get around using the .lib.
Good luck.
Related
I'm trying to link to the OpenAL soft library as compiled with the Media Autobuild Suite, and I'm getting the following error from Visual Studio:
libopenal.a(source.cpp.o) : fatal error LNK1143: invalid or corrupt file: no symbol for COMDAT section 0xA
My application is in C++ and compiled directly in Visual Studio 2019 (however, with the VS2017 toolset). OpenAL soft is written in C++ but exposes a C interface, and the MAB Suite compiles using MinGW/gcc and generates a libopenal.a static library file.
I've read from multiple other questions such as From MinGW static library (.a) to Visual Studio static library (.lib) and How to use libraries compiled with MingW in MSVC? that object files compiled with different compilers are generally not compatible for C++ due to name mangling, but often are compatible with C linkage. Because C does not use name mangling, and because the ABI is (usually) OS-dependent, libraries with a C interface compiled on the same platform are generally compatible.
Nevertheless, I've been running into linker errors, namely the LNK1143 above. I've confirmed that the included headers use extern "C" { to hint C linkage and that the target platform (x64) is the same for both builds. I also linked to libgcc.a as this answer recommends, and did not get any linker errors for it.
Does this mean the claim that C interfaces are generally compatible across compilers is not true? Or is this a special case in which it's not working? If the latter, what could be causing the linking to fail? Would I have better luck if I recompiled as shared libraries (dlls) instead of static libraries (even if I still use MinGW's .a files instead of .lib)?
I cannot change compilers from MSVC for my main app. I intend to use more libraries from the MAB Suite in the future, so I'd prefer to stay with MinGW for those dependencies if possible because I don't want to recompile all 70+ by hand.
Any help is appreciated. Thanks in advance.
Mixing compilers is tricky and prone to issues.
In some very simple cases it may work, but there are definitely a number of cases where you will run in to issues, for example:
if the different components use different runtime libraries
if memory management is being mixed (e.g. forget about freeing memory allocated with malloc() in MSVC using free() in MinGW)
when using exception handling in C++
My advice to do it all with the same compiler (and even the same version of this compiler).
Specifically in your case OpenAL can be built with MinGW-w64. So maybe you should look into that instead of downloading some prebuilt version from the web.
Or - somewhat easier - use MSYS2 and use its pacman package manager to get its own MinGW-w64 build of OpenAL.
I figured out what works for me, so I'll share.
I was not able to link a static library between compilers as I originally attempted. My understanding is that the extra info kept in the lib to allow link-time code generation is compiler-specific. Brecht Sanders's answer outlines a few possible reasons why the code wouldn't be compatible.
I was, however, able to link to a shared library, with a few extra steps.
Using the same suite (see the question), I compiled as shared and got libopenal.dll, libopenal.dll.a, and libopenal.def. In my case, the .def file was generated by the suite. Accoding to this answer, you can generate a .def file with gcc using:
gcc -shared -o your_dll.dll your_dll_src.c -Wl,--output-def,your_dll.def
Trying to link to libopenal.dll.a still gave me errors (I don't know exactly why, and I already discarded the logs.) What I did instead was generate a .lib file from the .def file. In Visual Studio's built-in terminal:
lib /machine:x64 /def:libopenal.def
This generated a libopenal.lib file in the working directory. Linking to this file worked perfectly, and I was able to successfully load the dll at runtime.
I've tested this same method with many other MinGW-compiled libraries from the suite, including libavformat, libavcodec, libavutil, libavdevice, swresample, and swscale, and thus far all of them have worked.
Kind of convoluted, but it seems to work well for me, so I hope this helps anyone else with the same problem.
While using C++ in Visual Studio 2013, I've come across a really weird warning/bug thing.
I have a static library and a console application.
Static library imports 4 3rd party .lib files, and their headers.
Console application imports the static library and the headers of the original 4 .lib files, so that I can use the code from the original 4 .libs and my .lib.
(I think this is the right setup in this situation, if there is a better way, do tell!)
However, when I build the static library, I get a warning: "LNK4221: This object file does not define any previously undefined public symbols, so it will not be used by any link operation that consumes this library" for each .lib imported.
But where is it getting the code if not from the libraries? If I remove the .libs from being imported, the build fails stating that it needs them! I don't know what to do in a situation like this. I would be happy enough to just leave the .libs being imported as is and ignore the warnings, but when I try to disable them (Under disable specific warning, "4221", in the compiler options), the warnings are not disabled!
Edit: The 4 3rd party .libs are standalone - they do not use each other's code so I do need to import all of them.
I am truly at a loss - any advice would be much appreciated.
I found a way of disabling the warnings using /ignore: on the linker command line, but I'm still confused as to why the linker gave the warnings in the first place, when removing the library as input caused multiple "unresolved external symbol" errors.
Oh well, problem (sorta) solved.
I'm using an object file built with Clang. But no matter what library arguments I pass to ld.exe, it seems to always spit back unresolved references, stuff like memcpy, Standard library, stuff, and implementation stuff like _cxa_atexit.
What libraries (and in what order?) do I need to pass to the MinGW linker to get it to link my object file into an executable?
Edit:
I changed the triple from "i686-pc-mingw" to "i686-pc-mingw32" and it solved most of the problems- Clang does the old D3D9 trick of "Silently fail when the input is clearly wrong and there's no way the output could be correct". But I'm left with just two unresolved externals- it's some std::_Hash_impl for float and double, with no change. The program is just "Hello, World!". Curiously, neither clang++.exe nor g++.exe have a problem with compiling the source, but if I compile it using the Clang C++ API to .o, and then pass it back to MinGW, I get the unresolved externals.
In general, it's not a good idea to use different toolchains when building a binary. It is entirely possible that the different tools' ideas of names of symbols won't match up.
Still, trying to answer your actual quesiton:
-lstdc would be a minimum requirement and -lstdc++ if it's C++ code. without knowing what your code does, it's impossible to say if you need more of them.
I made a program on Mac OS X using OpenGL and dynamically linking libpng. I'm now trying to port it to Windows. Whenever I try to compile and link my ported program in Borland it gives me this error and about 10 more that are the same, but with a different '_png_create_read_struct':
Error: Unresolved external '_png_create_read_struct' reference from C:\PROGRAMMING\PNGTEST.OBJ
I assume it's because I have not properly set up libpng with Borland C++ 5.5.1 for Win32. I've put png.h and pngconf.h into the include folder into C:\Borland\BCC55\Include, and I have put libpng12.dll.a, libpng13.a, libpng13.dll.a, libpng.a, libpng.dll.a, libpng12.def, libpng.def, libpng12.la, and libpng.la into C:\Borland\BCC55\Lib (there is probably no need for them all, but as a noob I have no idea which ones are needed and not).
Do I need to put a libpng.obj file in there too? And if so how would I make/get one? I have tried using makefile.bc32 to set up libpng, yet that gives me a missing separator error.
Here are my command-line options:
bcc32 -tW pngtest.cpp -lpng
I include png.h in my code. What am I doing wrong or is there an even better way to load images with alpha that doesn't need libpng, or even a better compiler to get for Windows?
You're probably better off with the MinGW compiler than Borland. Borland is not well supported any longer.
You could also download DevC++ and see if it has a libpng package in its addon mechanism.
DevC++ is an IDE that uses the MinGW C/C++ compiler.
That said, if you feel you must use BCC, you'll either have to
a) Build libpng with Borland. This is the best solution if you're going to use borland.
b) Use, I think, Impdef to create an import library from libpng.dll. You'll find impdef.exe or imp(something).exe in the borland bin directory.
Note that some libraries will not work with impdef as there is static code linked to the dll that causes it to fail without the proper runtime.
First of all, I would not have "polluted" the BC55 installation with third-party libraries; it will make moving the project to other build environments much more difficult. It would have been better to place them in a folder within your project.
Secondly do you know that the export library you are attempting to link is built for BC55? The .a extension suggests a GNU library (Borland libraries conventionally use .lib extension), in which case it would not link with BC55 which uses a different object file format. If this is the case you will need to rebuild the library as you attempted to do, so I suggest that you should really be asking a question about the problem you had with doing just that. I wonder whether the makefile is written for Borland make or GNU make, since they have differing syntax?
The command line option -lpng might be correct for GCC (where it will link libpng.a), but is meaningless to BCC. The -l option merely passes the text that follows to the linker. The linker command line, requires that the complete name be passed, and if no extension is provided, .lib is added implicitly.
You should probably just use coff2omf to convert the library. The DLL files are almost certainly in "Microsoft" COFF format.
See COFF2OMF.EXE, the Import Library Conversion Tool.
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.