I have a third-party LIB which has symbols exported as plain C/cdecl, so for example dumpbin.exe /SYMBOLS reports that both __imp_nvmlInit and nvmlInit are exported.
However in Visual Studio 2010 when I try to import them, the header file will have
extern "C" nvmlReturn_t nvmlInit(...);
but when I try to compile, I get the following error:
main.obj : error LNK2019: unresolved external symbol _nvmlInit referenced in function _main
How can I stop Visual Studio from looking for that symbol with a leading underscore? __declspect(dllimport) doesn't work because then it decorates to __imp__nvmlInit (one underscore too many).
Thanks.
That is a linker error. You need to link with the .LIB file associated with DLL, which will give the linker a promise that the function will be available at run-time when the DLL itself is loaded.
Related
I have the following files (https://www.dropbox.com/s/2bfhylzb2evrggp/Lib.rar?dl=0)
It contains the header file, .so and .dll file.
I added the aditional paths under C/C++ and Linker (to the dll.s and .h files)
I have also used the sample code in the rar file and VS2015 picks up the code
include "swi32.h"
But as soon as I try to use a method defined in the headerfile I get the following
Severity Code Description Project File Line Suppression State
Error LNK1120 1 unresolved externals ConsoleApplication1 C:\Users\Donald Jansen\Desktop\CPPTest\Swi32Test\ConsoleApplication1\Debug\ConsoleApplication1.exe 1
Error LNK2019 unresolved external symbol _WiCreateRawImage#0 referenced in function _main ConsoleApplication1 C:\Users\Donald Jansen\Desktop\CPPTest\Swi32Test\ConsoleApplication1\Console.obj 1
I am not sure what I am missing
If you are implicitly linking the dll, then you must have also received a .lib file which you need to link with your console application. This should remove the unresolved symbol warning. The operating system loads the DLL when the executable using it is loaded.
If you are explicitly linking the dll, then your code should explictly load and unload the DLL to access the exported functions.
The .so you mention probably is a linux shared object file and not useful on windows platform. I may be wrong though.
I downloaded and compiled GraphicsMagick, 1.3.23, Q16, x64, StaticMT version. I had to convert the Visual Studio 7 solution generated by GraphicsMagick's build utility to Visual Studio 2015 format. I linked my project to CORE_DB_magick_.lib and CORE_DB_Magick++_.lib.
When the linker ran, it produced unresolved external symbols when linking InitializeMagick() and DestroyMagick()
1>wtd.lib(WebController.obj) : error LNK2019: unresolved external symbol __imp_DestroyMagick referenced in function "public: __cdecl Wt::WebController::~WebController(void)" (??1WebController#Wt##QEAA#XZ)
1>wtd.lib(WebController.obj) : error LNK2019: unresolved external symbol __imp_InitializeMagick referenced in function "public: __cdecl Wt::WebController::WebController(class Wt::WServer &,class std::basic_string,class std::allocator > const &,bool)" (??0WebController#Wt##QEAA#AEAVWServer#1#AEBV?$basic_string#DU?$char_traits#D#std##V?$allocator#D#2##std##_N#Z)
I can't understand why the symbols are not being linked. Any ideas?
Apparently, GraphicsMagick Static versions do not link properly.
What is your project type? I had a similar problem when trying to link the GraphicsMagick libraries to a DLL.
The clue here is that __imp is the function decoration for DLL imports, so you're trying to link with DLL functions.
The problem is that the header magick/common.h, when linked to a DLL project, reads the current configuration of the Visual Studio pre-processor environment to determine which mode the library is in, which is obviously wrong if you're trying to link static libraries into your DLL, for example. In this case, it defines MagickExport to __declspec(dllimport).
AFAIK this is a bug in the library. For proper static build support, magick/common.h needs to do something like read information from the magick/magick_config.h to determine what mode the library was actually built in and define MagickExport appropriately.
Since your library is statically linked, you can fix this by commenting out everything in the define:
#if defined(MSWINDOWS) && !defined(__CYGWIN__)
and replacing it with:
#define MagickExport
#define ModuleExport
#define MagickGlobal
I know many people have asked about this error and trust me I've read ALL of them and followed all the steps! But I'm still getting the unresolved external symbol error.
I'm trying to use the dll of lp_solve (a linear programming package) in my c++ code in visual studio 2012.
The error message I'm getting is:
Error 80 error LNK2019: unresolved external symbol _make_lp#8 referenced in function "void __cdecl my_solve(BLAH BLAH)
The function make_lp() is from the lp_solve package and I'm calling it from my_solve() in my code. This error message pops up for each solver function I call. Seems the linker just couldn't find any of the implementation of these functions.
I've done the following
put #include "lp_lib.h" in my source code
put the .dll, .h and .lib files from the lp_solve package in the working directory and
added the path under Linker:General:Additional Library Directories.
added the lib under Linker:Input:Additional dependency
What's wrong?
Thanks for your help!
The problem I had was solved after realizing I downloaded the WIN64 package for lp_solve but my visual studio is using WIN32 as build platform (even though my machine is x86_64).
Using extern "C" may be helpful while including lp_lib.h in your .cpp as follows:
extern "C"
{
#include "lp_lib.h"
}
For more information, please check this link:
http://www.geeksforgeeks.org/extern-c-in-c/
I have created Regular DLLs Dynamically Linked to MFC.
in before build dll in dll project i used add another class. this class provide more method of constructor overloading.
Then I build dll successfully after i used this lib and dll file include project and then go to build and get linker error when using constructor overloading class
My Class Name: Object
Error 11 error LNK2001: unresolved external symbol "public: __thiscall AvinashiAMF::Object::~Object(void)" (??1Object#AvinashiAMF##QAE#XZ) BuleCappServiceUseDynamicDllDlg.obj
Error 10 error LNK2001: unresolved external symbol "public: __thiscall AvinashiAMF::Object::Object(enum AvinashiAMF::ObjectType,class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >)" (??0Object#AvinashiAMF##QAE#W4ObjectType#1#V?$basic_string#DU?$char_traits#D#std##V?$allocator#D#2##std###Z) BuleCappServiceUseDynamicDllDlg.obj
Error 12 fatal error LNK1120: 2 unresolved externals D:\Test Aplications\Visual Studio 2008\Projects\BuleCappServiceUseDynamicDll\Release\BuleCappServiceUseDynamicDll.exe
You're probably not exporting your class. See here http://msdn.microsoft.com/en-us/library/81h27t8c.aspx
Also, a nice tool to check for this kind of issues is depends.exe, included with Visual Studio, which allows you to check for exported and imported symbols.
There are two significantly different dynamic link libraries: implicitly linked and explicitly linked.
In short, implicitly linked is linked at the compile time. You need an import library to link with(.lib), header file with functions prototypes and properly usage of the dllexport and dllexport or use .def file.
dllexport/dllexport are easier to use in this case. System takes care of loading libraries (DLLs).
Explicit linking is a runtime linking. You do not need any import library or headers. You need to know what is the function signature. You have to explicitly call LoadLibrary and GetProcAddress to call the function.
To see how to properly create macros for export/import create empty Win32 project select DLL and make sure the Export symbols check box is checked.
In the main header file you will see explanation how to use macros for import/export.
Well i basically inherited a bunch of code that i was told to fix because it used to work a few months ago but it doesn't at the moment. The program itself seems to be riddled with linking errors and i was able to fix some of them. However I have run across a LNK2019 unresolved external _imp error where some function utilized in the main is not resolved. due to the "_imp" i am assuming that it is a problem related to importing from .dll or .lib files.
First of all i have three .lib files which i believe am importing them correctly into VS2010 and i have configured the platform to be 64x. There is also .dll files that correspond with the .lib files. The .h file that contains the declaration for these error ridden functions contain something like
ILAPI void ILAPIENTRY ilDeleteImage(const ILuint Num);
unfortunately i would be guessing that the definition is defined in the .dll file which i did not write myself so i am unsure. But since this is code that worked before i believe that i am getting this error because the linker can't find the definition rather than def/decl not matching reason.
when i hover over the ILAPI it states: "ILAPI __declspec(dllimport)"
My current guess is that the program imports the .lib files and the .lib files use the .dll files to get the definition of the functions. I believe that i am importing the .lib files since the compiler no longer keeps on telling me that it can't find specific .lib files. However i am concerned that it may not be connecting the the .dll files. I am some what unsure. I have opened the .lib files and the .lib files contain the names of the functions that are giving errors. I have also used the dependency walker program to look at my DLL files and it has been giving me some of the following errors:
Error: At least one module has an unresolved import due to a missing export function in an implicitly dependent module.
Error: Modules with different CPU types were found.
Based on other peoples comments i feel like i can ignore the 2nd error. But i am unsure of the first error. I am also unsure if that would be the root cause of the problem. It may or may not be.
I have also looked inside the .lib files using VS cmd and dependency walker and it seems like the names of the functions that can't be found are listed in one of the .lib and .dll.
In terms of configuration I am running on release mode x64 platform.
I have added "DevIL.lib ILU.lib ILUT.lib " library functions in the proj -> prop -> linker -> commandline. I have also added the path for linker -> general -> additional library directory. I have also tried messing with input additional dependency but it has no effect. The .lib and .dll files are put in the same directory as well. In the proj property configuration i do not mention .dll anywhere (am i supposed to? I've tried in various locations but just creates more error) I understand that there are a ton of posts regarding link 2019 error but i have not had good luck so far in my search for my particular problem. I would appreciate any suggestions, comment, or a link where i may find a clue as in to why this is occuring
here is the linker command from log:
here is the linker command from the build log itself:
Link:
C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\bin\x86_amd64\link.exe /ERRORREPORT:PROMPT /OUT:"x64\Release\dff.exe" /VERBOSE /INCREMENTAL /NOLOGO
/LIBPATH:C:\Users\Sub2\Desktop\dff\x64\Release /MANIFEST
/ManifestFile:"x64\Release\dff.exe.intermediate.manifest"
/MANIFESTUAC:"level='asInvoker' uiAccess='false'" /DEBUG
/PDB:"C:\Users\Sub2\Desktop\dff\x64\Release\dff.pdb"
/SUBSYSTEM:CONSOLE /OPT:REF /OPT:ICF /TLBID:1 /DYNAMICBASE /NXCOMPAT
/IMPLIB:"x64\Release\dff.lib" /MACHINE:X64
x64\Release\dff.exe.embed.manifest.res
x64\Release\acquisition.obj
x64\Release\azmemutil.obj
x64\Release\dff.obj
x64\Release\fft.obj
x64\Release\FocusMeasure.obj
x64\Release\ge.obj
x64\Release\stdafx.obj DevIL.lib ILU.lib ILUT.lib
1>LINK : warning LNK4075: ignoring '/INCREMENTAL' due to '/OPT:ICF' specification
// This is from Win32's <wingdi.h> and <winnt.h>
#if defined(__LCC__)
#define ILAPI __stdcall
#elif defined(_WIN32) //changed 20031221 to fix bug 840421
#ifdef IL_STATIC_LIB
#define ILAPI
#else
#ifdef _IL_BUILD_LIBRARY
#define ILAPI __declspec(dllexport)
#else
#define ILAPI __declspec(dllimport)
#endif
#endif
#elif __APPLE__
#define ILAPI extern
#else
#define ILAPI
#endif
Also:
#define ILAPIENTRY __stdcall
build log info when it gets close to error:
Found KERNEL32_NULL_THUNK_DATA
Referenced in kernel32.lib(KERNEL32.dll)
Loaded kernel32.lib(KERNEL32.dll)
Searching C:\Users\Sub2\Desktop\dff\x64\Release\DevIL.lib:
Searching C:\Users\Sub2\Desktop\dff\x64\Release\ILU.lib:
Searching C:\Users\Sub2\Desktop\dff\x64\Release\ILUT.lib:
Searching C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\lib\amd64\MSVCRT.lib:
Searching C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\lib\amd64\OLDNAMES.lib:
Searching C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\lib\amd64\msvcprt.lib:
Finished searching libraries
Finished pass 1
Invoking CVTRES.EXE:
/machine:amd64
/verbose
/out:"C:\Users\Sub2\AppData\Local\Temp\lnk92ED.tmp"
/readonly
"x64\Release\dff.exe.embed.manifest.res"
Microsoft (R) Windows Resource To Object Converter Version 10.00.30319.01
Copyright (C) Microsoft Corporation. All rights reserved.
adding resource. type:MANIFEST, name:1, language:0x0409, flags:0x30, size:2
1>dff.obj : error LNK2019: unresolved external symbol __imp_iluGetImageInfo referenced in function main
1>dff.obj : error LNK2019: unresolved external symbol __imp_iluImageParameter referenced in function main
1>dff.obj : error LNK2019: unresolved external symbol __imp_ilDeleteImages referenced in function main
1>dff.obj : error LNK2019: unresolved external symbol __imp_ilSaveImage referenced in function main
1>dff.obj : error LNK2019: unresolved external symbol __imp_iluFlipImage referenced in function main
1>dff.obj : error LNK2019: unresolved external symbol __imp_iluScale referenced in function main
1>dff.obj : error LNK2019: unresolved external symbol __imp_ilTexImage referenced in function main
1>dff.obj : error LNK2019: unresolved external symbol __imp_ilCopyPixels referenced in function main
1>dff.obj : error LNK2019: unresolved external symbol __imp_ilGetError referenced in function main
1>dff.obj : error LNK2019: unresolved external symbol __imp_ilLoadImage referenced in function main
1>dff.obj : error LNK2019: unresolved external symbol __imp_ilBindImage referenced in function main
1>dff.obj : error LNK2019: unresolved external symbol __imp_ilGenImages referenced in function main
1>dff.obj : error LNK2019: unresolved external symbol __imp_ilInit referenced in function main
1>dff.obj : error LNK2019: unresolved external symbol __imp_ilGetInteger referenced in function main
1>dff.obj : error LNK2019: unresolved external symbol __imp_ilEnable referenced in function main
1>dff.obj : error LNK2019: unresolved external symbol __imp_ilOriginFunc referenced in function main
1>x64\Release\dff.exe : fatal error LNK1120: 16 unresolved externals
1>Done Building Project "C:\Users\Sub2\Desktop\dff\dff.vcxproj" (rebuild target(s)) -- FAILED.
Build FAILED.
Just in case i have also tried writing #define _IL_BUILD_LIBRARY but has no effect.
I'm adding an answer here to summarize a bit on the above comments, the probable root cause and finding a solution to the unresolved errors. I'll preface this by saying linkers tend to be dumb low level tools. If the symbols referenced in the object files don't match exactly with the library then the build process bails out with those unresolved errors. Therefore, the author of the dll library and clients using it will need to put in some effort to ensure the symbols agree.
Root Causes
Unresolved errors are usually caused by one of the follow:
Neither the project nor the libraries linked against implement the function for that symbol.
The libraries actually do implement the function but under a differing reference symbol.
The headers for the library aren't preprocessed or decorated correctly thereby causing #2.
The Hunt
Base on what the OP described the dll libraries linked against exposes a C API. It is unclear what calling convention is being followed by the library in question. The exported names in the dll contain plain undecorated function names suggesting a __cdecl convention. The provided corresponding headers, OTOH has a function like:
ILAPI void ILAPIENTRY ilDeleteImage(const ILuint Num);
which expands into this after preprocessing:
__declspec(dllimport) void __stdcall ilDeleteImage(const ILuint Num);
From this you can conclude three possible scenarios:
The unresolved functions follow a __cdecl convention and the provided headers are wrong.
The unresolved functions follow a __stdcall convention and the exported dll names are wrong.
The functions follow __stdcall but are undecorated to look like __cdecl in the dll. This suggest that a .def file might have been used to build the dll in question.
A Sad State of Affair
Unfortunately, the function call convention followed in a win32 dll is in a confusing state of affairs. There's nothing in the language standard, C or C++, that addresses this ABI issue. See my other answer here. The toolchain vendor is free to decorate the names however they like but typcially for __cdecl functions it's plain undecorated or with a prefixed leading _ underscore.
WinAPI functions you find, like in kernel32.dll user32.dll gdi32.dll etc. are also undecorated but yet follow __stdcall. However, MSVC itself decorates __stdcall with a trailing ampersand with total bytes of the parameters(eg. ilDeleteImage#4) thus contributing to the confusion. To override how LINK decorates the functions, you have to provide a .def file that specifies the new name alias. See here for more details.
Finding the Real Convention
Assuming you don't have access to the source used to build the dll, there are two approachs I can think of to identify the real convention used.
Create a minimal test application that calls into the dll functions as if it uses __cdecl and see if it crashes and burns. This is the easier more straightforward method and you don't have to understand assembly to do it.
Second approach, you do the same but insert assembly breakpoints into your test application and run it through the debugger doing single step instructions. Make sure to choose a dll function taking at least one parameter. For example:
// pullin dll headers
// etc..
int main()
{
__asm int 3;
ilDeleteImage(0xdecafbad);
}
This will break and give control back to the debugger right before the dll function call. From here single step at the assembly level until you reach ilDeleteImage's function prologue.
; function prologue
push ebp
mov ebp, esp
; function implemention
; more opcodes here
; ...
; function epilogue
mov esp, ebp
pop ebp
ret 0x8
Check what form of ret is being used on function return. The number argument following the ret mnemonic indicates how much to increment the esp stack pointer. Any number >0 suggestes a __stdcall function. The hypothical disassembly above shows a __stdcall function freeing 8 bytes on the stack which also hints that this function takes 2 arguments.
I had this compile error while building a project using external static libraries, QDBM and PCRE:
_main.obj : error LNK2001: unresolved external symbol __imp__dpversion
_main.obj : error LNK2001: unresolved external symbol __imp__regcomp
I had correctly configured these external projects to build static libraries, but I had forgotten to define the correct preprocessor defines in my own code, which used these libraries, to enable static linking.
So when they imported the headers from QDBM and PCRE, they added a __declspec(dllimport) that shouldn't be there (for static linking), so they were trying to import symbols from DLLs that didn't exist.
I added the missing preprocessor defines to my build system, which fixed the error:
-DQDBM_STATIC -DPCRE_STATIC
Which meant adding the following lines to my CMakeLists.txt file:
# Tell QDBM not to build itself as a DLL, because we want to link statically to it.
target_compile_definitions(qdbm PUBLIC -DQDBM_STATIC)
target_compile_definitions(lib_common PUBLIC -DPCRE_STATIC)