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What is an undefined reference/unresolved external symbol error and how do I fix it?
(39 answers)
Closed 5 years ago.
I have inherited a legacy project which utilizes some external functions from a *.lib. From what I was told, the syntax for using the *.lib was correct and this
was buildable in whatever visual studio version they used. (ie, there is an extern "C" prototype file, and all the function signatures are correct).
When building, I get "error LNK2019: unresolved external symbol _A86_ReadConfigReg#12 referenced in function ..."
I'm pretty confident that this is related to the *.lib file since the *.lib file has "A86" in the name...There is also a *.dll with the same name.
I went to project properties -> Linker -> Input and listed the *.lib file name in "Additional Dependencies", but no luck. I tried adding the include directories, copying the *.lib & *.dll to the executable location. But no luck.
How do I go about fixing this error?
First thing you should do is inspect the library to make sure the referenced function is there. Start an msvc developer command prompt, and run dumpbin.exe
Syntax:
dumpbin /exports <full path library name>
This will give you a listing of all exported symbols from the library.
You'll get a clearer idea of what to do from there.
[EDIT]
dumpbin told you that your lib exports a function called A86_ReadConfigReg, which is a __cdecl signature and not a __stdcall signature like _A86_ReadConfigReg#12 that your linker expects.... At least two things you should do/check in order of priority.
Your linker is looking for a pascal call signature and this is very odd. Does your project have __stdcall as a default for function calls? That's controlled by the /Gz switch in Project Properties->C/C++->Advanced->Calling Convention. Default should be set to __cdecl (/Gd)
You should check that your include files enclose all the function declarations in an extern "C" { } block. If they don't, you can place the block around the #include directive, so you do not have to modify the library's files.
Like so:
extern "C" {
#include <mylib.h>
}
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'm trying to add Beecrypt library to my project. First i have added header files but after attempting to create an object i'm receiving the following errors:
error LNK2019: unresolved external symbol "__declspec(dllimport) public: virtual __thiscall beecrypt::security::SecureRandom::~SecureRandom(void)" (__imp_??1SecureRandom#security#beecrypt##UAE#XZ) referenced in function _wmain
As far as i understand it is due to the absence of cpp files. Ok. Then i'm trying to add cpp files but whatever folder i put them i still receive the same error. For example SecureRandom.h is situated:
beecrypt/c++/security/SecureRandom.h
Where should i put SecureRandom.cpp to get rid of that error? I've already tried all levels of folders. Or maybe that error is caused by something else? Thanks a lot in advance
Simplest way is to Just drag and drop them to your project in the solutions explorer.
Or
Follow the steps given in the link below on MSDN website:
Adding a Source File.
Okay, here's the thing. I have all the IL files I need, namely
DevIL.dll
DevIL.lib
ILU.dll
ILU.lib
ILUT.dll
ILUT.lib
config.h
config.h.in
devil_cpp_wrapper.h
devil_internal_exports.h
il.h
ilu.h
ilu_region.h
ilut.h
ilut_config.h
My project directory looks like this, let's say my project's name is "Project1"
|-Debug---Project1.pdb
|
| |---Debug---[loads of files]
| |
| |---Glut---[OpenGL files]
| |
| |---IL---[all the files mentioned above]
|-Project1---|
| |---image.bmp
Project Folder---| |
| |---[header and .cpp files I made in the project]
| |
| |---[files produced by Visual Studio]
|
|-ipch---[unrelated stuff]
|
|-Project1.sln
|
|-[other files VS created]
I've put all the DevIL files in the IL folder, as mentioned, and I am sure I am using the unicode compatible versions of them, as I am using Unicode Character Set for the project. In my "Additional Dependencies" I have
ilut.lib; ilu.lib; DevIL.lib;
So, the dependencies are there, I know that's not the problem.
After all that, I am still getting linker errors, mainly LNK2019:unresolved external symbol__imp_ for all the IL functions.
What am I missing? It looks to me like maybe something to do with the project properties or the files themselves...maybe I missed a file?
EDIT: Here is the output messages
1>------ Build started: Project: Final Year Project, Configuration: Debug Win32 ------
1>Build started 29/4/2011 12:46:04 pm.
1>InitializeBuildStatus:
1> Touching "Debug\Final Year Project.unsuccessfulbuild".
1>ClCompile:
1> Main.cpp
1>c:\users\xxxx\desktop\final year project 0.2\final year project\main.cpp(152): warning C4390: ';' : empty controlled statement found; is this the intent?
1>c:\users\xxxx\desktop\final year project 0.2\final year project\main.cpp(141): warning C4101: 'alpha' : unreferenced local variable
1>ManifestResourceCompile:
1> All outputs are up-to-date.
1>Main.obj : error LNK2019: unresolved external symbol __imp__ilInit#0 referenced in function "public: static void __cdecl Main::Init(int,char * *)" (?Init#Main##SAXHPAPAD#Z)
1>Main.obj : error LNK2019: unresolved external symbol __imp__ilDeleteImages#8 referenced in function "public: static void __cdecl Main::DisplayScene(void)" (?DisplayScene#Main##SAXXZ)
1>Main.obj : error LNK2019: unresolved external symbol __imp__ilGetData#0 referenced in function "public: static void __cdecl Main::DisplayScene(void)" (?DisplayScene#Main##SAXXZ)
1>Main.obj : error LNK2019: unresolved external symbol __imp__ilConvertImage#8 referenced in function "public: static void __cdecl Main::DisplayScene(void)" (?DisplayScene#Main##SAXXZ)
1>Main.obj : error LNK2019: unresolved external symbol __imp__ilGetInteger#4 referenced in function "public: static void __cdecl Main::DisplayScene(void)" (?DisplayScene#Main##SAXXZ)
1>Main.obj : error LNK2019: unresolved external symbol __imp__ilLoadImage#4 referenced in function "public: static void __cdecl Main::DisplayScene(void)" (?DisplayScene#Main##SAXXZ)
1>Main.obj : error LNK2019: unresolved external symbol __imp__ilBindImage#4 referenced in function "public: static void __cdecl Main::DisplayScene(void)" (?DisplayScene#Main##SAXXZ)
1>Main.obj : error LNK2019: unresolved external symbol __imp__ilGenImages#8 referenced in function "public: static void __cdecl Main::DisplayScene(void)" (?DisplayScene#Main##SAXXZ)
1>C:\Users\xxxx\Desktop\Final Year Project 0.2\Debug\Final Year Project.exe : fatal error LNK1120: 8 unresolved externals
1>
1>Build FAILED.
1>
1>Time Elapsed 00:00:01.93
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========
Since you added the build output, the answer is now easy: your linker errors have nothing to do with DevIL at all.
You need to link to SDL (Simple DirectMedia Layer).
Since SDL has a C interface, and - IIRC - doesn't require that the DLL uses the same heap as the application, the VC8 version of the "Development Libraries" should do fine (even if you use VC10). Just add SDL.lib to the "Additional Dependencies" and you should be fine.
EDIT
OK.
You're either
not linking against the required .lib files (DevIL.lib etc.) or
linking against corrupted/wrong .lib files
At least there is no other explanation I can think of.
The names mentioned in your build log (__imp__ilInit#0 etc.) are correct, and the current "DevIL SDK" (DevIL 1.7.8 SDK for 32-bit Windows) works fine with VC10 (I just verified it).
To assure you're linking against DevIL.lib etc. please put the following in your main.cpp file:
#pragma comment(lib, "DevIL.lib")
#pragma comment(lib, "ILU.lib")
#pragma comment(lib, "ILUT.lib")
To make sure you're linking against the correct version of those files, re-download the whole SDK and try again with the new files.
EDIT 2
Since I got half the reward, I feel I should be more helpful :)
One last thing you can try: enable verbose linker output to check if the linker finds the correct version of DevIL.lib. (If it didn't find any DevIL.lib, you would get an error LNK1104: cannot open file 'DevIL.lib' - and since you're not getting that message, that cannot be the problem.)
To enable verbose linker output, add the /VERBOSE switch (under Configuration Settings -> Linker -> Command Line -> Additional Options).
That will give you a ton of messages. Copy them into your favorite editor, and search for lines containing DevIL.lib. One of the lines should read Searching X:\path\to\DevIL.lib: - that's the path to the copy of DevIL.lib the linker is using. If that's not the path where you copied the files from the SDK you downloaded, you have found the problem.
And if there are no lines containing DevIL.lib, then the linker isn't even trying to locate it. However I've never seen #pragma comment fail, so if you indeed added those lines that almost surely cannot be the case.
BTW: please let me know if you managed to solve this. This is so strange that I really want to know what was going on :)
You need to tell the linker to link against the IL libs.
Project settings, Linker, Input
Make sure the directory the libs are in is in the Additional directorys field too.
I've noticed your config.h.in file should have .win extension because that it is in DevIL-SDK-x86-1.7.8.zip package. And there's no devil_cpp_wrapper.h file also.
Finally i solved this in this way:
Header files
config.h
config.h.win
devil_internal_exports.h
il.h
il_wrap.h
ilu.h
ilu_region.h
ilut.h
ilut_config.h
goes to VC include directory - all in one directory named IL (c:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\IL\ by default)
Liblary files
DevIL.lib
ILU.lib
ILUT.lib
goes to lib directory (c:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\lib\ by default)
DLL files
DevIL.dll
ILU.dll
ILUT.dll
goes to project dorectory (...\Project Folder\Project1\ in your case)
Then i added liblary files to project by right click on project->Properties->Linker->Input->Additional Dependencies (wrote just name of liblaries like ILU.lib)
In my project I just include IL\il.h, IL\ilu.h and IL\ilut.h
I think you may got wrong files by the way...
Just in case you never got this worked out, or anyone else has the same problem (like I did):
I had downloaded the 64-bit version of DevIL for my 64-bit Windows computer, but Microsoft Visual Studio (I was using Express) was the 32-bit version.
I downloaded the 32-bit version of DevIL and it worked!
I had the same problem. Seems like the pre-built binaries are swapped: I could link to the ones designated as non-unicode but they would utterly fail trying to use my non-unicode strings and return unicode strings. Try to build your own binaries from the source or use a previous version.
you should compare the function signatures that you see in your errors with the signatures you get with depends.exe (depedency walker). If they differ there may be a compiler-issue.
You may then try to compile with :
extern "C" {
// put your devils-include directives here ...
}
Nothing garantied of course , just a suggestion.
You may also check the 'Additional Library Directories' property on your 'Linker\General' page to see if (when used) it points to the right directory for your build (if you also added a path to the standard VC lib-directories their may be a conflict ,use either one but not both).
Another suggestion is to create a new project and do it all over again ,you may have made an ever so little mistake.
Good luck !
I had the same problem.
In my case it was problem with code in all devil`s .h files
#ifdef _WIN32
#if (defined(IL_USE_PRAGMA_LIBS)) && (!defined(_IL_BUILD_LIBRARY))
#if defined(_MSC_VER) || defined(__BORLANDC__)
#pragma comment(lib, "%LIBNAME%.lib")
#endif
#endif
#endif
after second #if code was deactivated.
i added #pragma comment(lib, "DevIL.lib") (and 2 more) into my main.h and linker errors dissapeared.
sorry for my bad english =[
I don't know if this question is still active, but since it has no chosen answer, I'll post this. I had what seems like the exact same problem with DevIL version 1.7.8. To fix it, I rolled back the version to 1.7.7 and used #undef _UNICODE before including the headers and #define _UNICODE afterwards. The project compiled without linker errors and worked without a hitch. On 1.7.8, the libraries seem to all be unicode, or at least they don't seem to support ascii very well. However, this may just be some weird compatibility issue with my computer as it does not seem to be a common problem
It might be that you have to declare some preprocessor variable to actually tell the compiler that you are importing symbol; I mean something related to __declspec( dllimport )
I did exactly as what Sarah said about the 32-bit or 64-bit Visual Studio versions. I'm on a 64-bit computer running a 32-bit Visual Studio 2012. I obtained this error when I used the x64 DevIL files. Getting the x86 version helped. Here's the basic steps I took to ensure it does run:
Right-click your project and go to Properties.
Under C/C++ > General, add DevIL's 'include' folder under Additional Include Directories.
Then under Linker > General, add DevIL's 'lib' folder (it should contain: DevIL.lib, ILU.lib and ILUT.lib) to Additional Library Directories. For x64 it may not contain a lib folder, it may be just the DevIL directory itself (for version 1.7.8 it was that case).
Also in Linker > Input, add those .lib file names into Additional Dependencies.
Now that should be all you need to do in the project properties. In the main.cpp you should include the appropriate header files and it should work when you initialize.
Example:
#include "IL/il.h"
#include "IL/ilu.h"
#include "IL/ilut.h"
int main(){
ilInit();
iluInit();
ilutRenderer(ILUT_OPENGL); //these are just to initialize
}
Does anybody know about this linker error in Visual C++?
PGPkeys.obj : error LNK2001:
unresolved external symbol
_imp_PGPclCloseClientPrefs
Unresolved externals are usually due to missing binary (a DLL or a static lib). Check directory paths to libraries your code needs.
You need to find out in what library/DLL the symbol PGPclCloseClientPrefs is defined.
If mbadawi23's answer doesn't solve your problem, think about the following:
I think imp might indicate an environment mismatch, so make sure you're using the linker that came with VC++ 6. I do not remember VC++6 mangling imported/exported symbol names in that way, but, I could be wrong.
If worst comes to worst, look up making a def file for the DLL in which PGPclCloseClientPrefs lives and export the symbol that way.