This question already has answers here:
What is an undefined reference/unresolved external symbol error and how do I fix it?
(39 answers)
Closed 5 years ago.
I tried multiple PDF lybrary and MUPDF is my last chance to build my own small PDF application. But here I also have problems. Before that I had problem with LNK4098: defaultlib 'MSVCRT', but I solved that to set for all MUPDF library /MDd version. Most errors is solved after that, but still I can't to solve this:
error LNK2001: unresolved external symbol "void __cdecl pdfapp_open(struct pdfapp_s *,char *,int)" (?pdfapp_open##YAXPEAUpdfapp_s##PEADH#Z)
//more 3 errors
As MuPDF written on C, I do this:
extern "C" {
#include <pdfapp.h>
#include <mupdf\fitz\context.h>
}
But I get this errors:
error LNK2001: unresolved external symbol pdfapp_open
//more 3 errors
There is only three functions what I use in my application. I checked libs and headers linking, I set my project Debug, x64, /MDd also but I get the same.
Honestly, I can't find this three functons in no one libs. I'm not a expert in programming but I know that functions strings should be finding in libs, doesn't? What does mean this errors in my case?
Either your linker is failing to find the import library for mupdf or you have a name mangling/decoration type issue.
Once you download and build mupdf, there should be an import library for you to link to. Are you linking to it? Look in your project linker settings under Linker >> Input >> Additional Dependencies. Have you added such an import?
If not, add it in. It shouldn't be hard to find. It is likely right next to the mupdf DLL that you downloaded (or built).
Assuming you have added it, your next step is to verify that you are properly finding it. Look at the build output. Are you getting a warning about it? No, change the Linker >> General >> Show Progress to "Display all progress messages" and build again. Is there a warning about the library or function?
Last possibility that I can think of is that the DLL is actually exporting its functions as C++ (i.e. with name decoration), not as extern "C". In that case and your extern "C" brackets don't belong there. Or perhaps vice versa (i.e. maybe you failed to use extern "C" in all places you #include it). I can see that your example uses it but is that all the places?
If you are building the mupdf.DLL be sure it is being built the same way and with the same calling convention as your client code.
Related
I am trying to use CImg library for some image processing task. Using VS 2012 on Windows 7 x64, I am building a project to create dll that I need for my application. I have included the only header file CImg.h from the library. But as soon as I initialize an CImg object, I get bunch of unresolved external symbol errors. One sample error is as follows:
layer.obj : error LNK2019: unresolved external symbol __imp_SetDIBitsToDevice referenced in function "public: struct cimg_library::CImgDisplay & __cdecl cimg_library::CImgDisplay::paint(void)" (?paint#CImgDisplay#cimg_library##QEAAAEAU12#XZ)
Can anyone explain to me what am I doing wrong and how to fix it? (I am a newbie when it comes to C++ terminologies.)
there is nothing other than the header file in the CImg library to link to.
You cannot link to a header file. If it is a header-only library, then you do not need to link anything. You include the header file and the functions it defines are compiled directly. That appears to be the case for CImg; the documentation says it is a self-contained template library that consists of only a single header file. So indeed, all you need to do is include it and you're off to the races.
The unresolved external symbol errors are coming from somewhere else. You have to read the error messages and look at the function names to see where.
A couple of hints:
The __imp_ prefix suggests that you're looking at a Windows API function.
If you didn't know that, you could always ignore the prefix and Google the readable part of the name, in this case, SetDIBitsToDevice. Chances are very good you'll turn up the documentation or at least something that points you in the right direction.
Indeed, in this case, you get right to Microsoft's SDK documentation for the SetDIBitsToDevice function. It's a Windows API function alright, and Microsoft's documentation always tells you what library you need to link to in order to consume it. Look at the bottom of the page:
Header: Wingdi.h (include Windows.h)
Library: Gdi32.lib
DLL: Gdi32.dll
The CImg library header file has obviously already included the Windows.h header file, or you'd have gotten a compile-time error. You're getting a linker error, which means that you have not told the linker to link in the Gdi32.lib library. This is what will allow you to call GDI functions. It is a stub that facilitates calling functions exported from Gdi32.dll.
In general, when building a Windows application, you will want to link with, at minimum, kernel32.lib, user32.lib, and gdi32.lib.
This question contains more information on dealing with undefined symbol errors, and also how to configure your linker. In Visual Studio, go to Project Properties → C/C++ → Linker → Input → Additional Dependencies. Or add #pragma comment(lib, "gdi32.lib") to a source file (your precompiled header is a good place, usually named StdAfx.h).
This function is part of the win32 API, specifically in GDI. You need to change your project settings to link with Gdi32.lib
https://msdn.microsoft.com/en-us/library/windows/desktop/dd162974(v=vs.85).aspx
I've got an NIUSB8452 DAQ, with which the vendor thoughtfully provided ni845x.lib and ni845x.h so I could use C instead of LabView to do my data reading. However, I'm having some problems with getting the lib working in VisualStudio 2015. The first point of alarm is probably that their documentation says it is compatible with VS6, but I've seen other people on here successfully use libraries for VS6 on VS15, so, I hope I can also be so beautiful.
The problem that I am having right now is that on a build, I'm getting linker errors that read something like
unresolved external symbol #ni845xStatusToString#12 referenced in function (function name follows)
While googling around, I found this question which mentioned dumpbin /exports. To check that I wasn't running into a 32/64 bit error like the poster described (since I wasn't really sure how to diagnose this, it seemed as good a place to start as any), I ran dumpbin /exports on the external lib. I got a pile of public symbols, including
FF06 __imp__ni845xStatusToString#12
FF06 _ni845xStatusToString#12
I'm definitely not seeing #ni845xStatusToString#12, which is what VisualStudio is complaining about being unresolved.
What's the difference between #ni845xStatusToString#12 and _ni845xStatusToString12? What does the presence of the latter and the absence of the former indicate that I am doing wrong with this import?
Notes
The lib and header have been included in the file as described in this question, with the exception that I gave a full path to the lib for #4, which I think implies you only need the filename.
I'm using extern "C" { #include ni845x.h } in my cpp file, although ni845x.h does have the #ifdef __cplusplus boilerplate in there.
I'm making a C++ program and I want to use FFmpeg pre-built for x64, which is a C-compiled library.
I'm using this code in order to include its header:
extern "C" {
#include "libavcodec/avcodec.h"
#include "libavformat/avformat.h"
#pragma comment (lib,"G:/Documents/ffmpeg/lib/avcodec.lib")
#pragma comment (lib,"G:/Documents/ffmpeg/lib/avformat.lib")
}
I'm then calling the symbols like I would do for a normal function, for example with av_interleaved_write_frame(out->formatContext, &packet);
However, when I try to compile it with Visual Studio 2015's built-in C++ compiler, I get a lot of error like
Error LNK2019 unresolved external symbol _av_write_trailer referenced in function "void __cdecl closeArenaVideo(struct VideoOutput *)" (?closeArenaVideo##YAXPAUVideoOutput###Z) Sparta2 c:\Users\Théo\documents\visual studio 2015\Projects\Sparta2\Sparta2\video.obj
for basically any of the symbols I'm refering to.
I tried to import everything in Visual Studio, to compile with command-line, to manually put FFmpeg's libraries in the default libraries path, without success.
Thank you in advance!
A typical problem which is hard to understand from quoted linker errors is the problem of referencing wrong .lib files, esp Win32 platform libraries in x64 build and vice versa. The names might be correct, but the set is wrong and then linker takes the #pragma references but ignores the content.
You should make sure that your build platform matches the bitness of referenced library files. This answer has minimalistic project which does build well and you can compare code/references to what you use, and it also mentions bitness problem as well in the very bottom and comments to the answer.
I added some boost stuff* to my code and the linking phase failed with:
error LNK2019: unresolved external symbol _IsolationAwareLoadLibraryA#4 referenced in function "void * __cdecl boost::interprocess::winapi::load_library(char const *)" (?load_library#winapi#interprocess#boost##YAPAXPBD#Z)
Can anyone help me figure this out? kernel32.lib is added in linker settings. I searched for _IsolationAwareLoadLibraryA and it doesn't seem to be present in Windows SDK 6.0A, which I'm using. The project is CLR if that matters.
*the boost stuff are two shared memory headers:
#include <boost/interprocess/shared_memory_object.hpp>
#include <boost/interprocess/mapped_region.hpp>
This functions are part of SDK 7.0A, and they should be inline (so there's no need to specify an .lib file). Try downloading and using a newer SDK, and make sure that ISOLATION_AWARE_ENABLED gets #defined, because this is what triggers the inclusion of those functions. I guess boost should define it by itself though.
It turned out the project I used had a "ISOLATION_AWARE_ENABLED=1" added to preprocessor definitions. Removing it fixed the linker error. Not sure whether this won't cause any other problems though. The disturbing fact is that I'm wasting lots of time just resolving various issues related to building my project with third-party C/C++ libraries.
This question already has answers here:
What is an undefined reference/unresolved external symbol error and how do I fix it?
(39 answers)
Closed 8 years ago.
I've got this MFC application I'm working on that needs to have an embedded database. So I went hunting for a slick, fast "embeddable" database for it and stumbled accross SQLite.
I created a DB with it, and I created a static library project with Visual Studio 2008. the library project will be used in another main project.
In the library project, I created a class DBClass with a method AddFeedToDB(CFeed f). The library project uses the .lib file from codeproject (cppsqlite3.lib).
When compiling the static library, no error is detected, but when I try to use the library project file in the main project, I get these type of errors:
error LNK2019: unresolved external symbol "public:void __thiscall
CppSQLite3DB::close(void)" (?close#CppSQLite3DB##QAEXXZ
referenced in function "public: int __thiscall
CTalkingFeedsDB::AddFeedToDB(class CFeed,char const*)" (?
AddFeedToDB#CTalkingFeedsDB##QAEHVCFeed##PDB#Z
What am I missing?
I know it is already 2 years since this question... but i run in the same situation here. Added all the header files... added the lib directories.. and keep having this error.
So i added manually the lib to the Configuration Properties -> Linker -> Input -> Aditional Dependencies
and all works for me.
It happened to me more than once that I thought symbol XXX (i.e. ?close#CppSQLite3DB##QAEXXZ) was in the import lib, while the actual symbol was __impXXX (i.e. __imp?close#CppSQLite3DB##QAEXXZ).
The reason for the linker error is then to be found in the compilation step: the compiler will generate the ?close#CppSQLite3DB##QAEXXZ symbol to be imported, where it should generate __imp?close#CppSQLite3DB##QAEXXZ. This often means that the function declaration itself didn't have __declspec( dllimport ). Which may be caused by some preprocessor symbol not being defined. Or the __declspec not being there at all...
Don't know if it is your case, but the imp prefix may mean that you are compiling a x64 library in a Win32 project.
You either need to link the codeproject SQLite lib to your executable, or to include the sources files in your project directly. (Which one did you do ?)
I would follow these steps:
think about what library or .obj file you expect the symbol to be exported by.
check whether it actually does export that very symbol (check character-wise). Sometimes, it's the calling convention differs.
check if the library you expect to contain the symbol is known to the linker - first check for the 'additional libraries', then check if the library is actually found (I mostly do this by using filemon.exe from sysinternals, and look for link.exe to open the lib file. )
After thinking a while, you may find that your library project will not export the sought for function. That function is in the database lib. You should add that lib to your main project. It's no use adding it to your static lib project.
The compiler and linker will not link one library into another (unless one is a DLL). You need to specify both libraries (cppsqlite3.lib and your own static library) in your main project.