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 have a project with source code, and a TestProject in same solution.
The test file using GTest framework in the TestProject has got an #include of the header file Composite.h from main project.
In the body of the first GTest, I instantiate the Composite class declared in the Composite.h. This line gives a compile error LNK2001: unresolved external symbol on each of the private methods of the Composite class.
Code in the myTest.cpp file looks like that
#include "Composite.h"
TEST(testComposite, testCase1)
{
Composite c; // error LNK2001
// my test here;
}
What's wrong with this instantiation ?
EDIT
I linked to the library containing the implementation of private methods in Composite class. Also, i tried alternatively to #inlcude the .cpp for the source code of this class. Either solution do not fix the problem.
EDIT -- QUESTION
Can this be that the folder with the moc files for the Composite classes and its parent class (with Q_OBJECT defined) are unseen ?
I tried adding in the Test Project properties' additionnal Directories the folder containing the moc files. This does not work either.
There should be nothing wrong with the instantiation. I assume that there is a Composite.cpp that contains your missing or unresolved code.
You will need to add this Composite.cpp into your project or link your application to the library that contains the Composite.cpp
The includes have nothing to do with the linking of a program. What you include matters for the compilation and that occurs before the linkage. To resolve the problem you show here, you need to link with whatever(object file, library) contains the implementation of the private methods you mention.
Related
My project is to build a stack in C++, And I implemented it using array ,but I have 6 Errors: all of them
LNK2019 Unresolved external symbol to some functions implementation in the .CPP file I know this is a linker errors , the problem occurred when I Divided My code into Header files .h and implementation files .cpp but the syntax is alright and the program The program has run correctly when I had to test the code in on file :the main file ,any solutions please?
this is the link of code:
https://github.com/MohamedYehiaShahin/stack-usin-array-c-
Since you didn't post your code, I can only guess. If you are implementing your stack using a template (very common) then you may see this error if you define your template functions/methods in a separate .cpp file. Typically template functions & classes are defined inline or contain their definitions within the same header file as their declarations.
Very new to C++ and the VS IDE, and I'm trying to start working with Dear imGUI and openGL with a hello world function. I've added resources with lib and dll files before for c++ (for openGL), but not something like imGUI which only has .h and .cpp files - feels like I'm struggling to understand how to inform VS of where those are and how they link up.
Here's an example of an error I saw when building:
Severity Code Description Project File Line Suppression State
Error LNK2019 unresolved external symbol _glfwGetWindowSize referenced in function "void __cdecl ImGui_ImplGlfw_NewFrame(void)" (?ImGui_ImplGlfw_NewFrame##YAXXZ) imGUITrial1 ..\Coding\imGUITrial1\imgui_impl_glfw.obj 1
So I opened up imgui_impl_glfw and found the function, and it appears to reference a function declared in glfw3.h...but that function looks like just a declaration, with no definition. I had previously added each folder with these files in it to the project additional directories, so I went ahead and added glfw3.h as a resource to my sources folder in the solution as well. That didn't change anything, so now I'm not sure how to find where the function is actually defined, or if the issue is that I need to somehow tell VS that this file exists in a another nested properties window?
Maybe it will help to have a screenshot of the solution. These are largely files copied from the github that I haven't changed (which I chose from looking through the backend examples), so I don't think I broke anything in the files themselves.
enter image description here
I'm stuck in a linker error and need some help. I'm using MSVC.
At the beginning, I made this:
/* graphics_app.h */
#ifndef DK_GRAPHICS_APP_H
#define DK_GRAPHICS_APP_H
...
class GraphicsApp {
private:
static GraphicsApp* self;
...
};
GraphicsApp* GraphicsApp::self = nullptr;
#endif /* DK_GRAPHICS_APP_H */
This header used to work... and I made some improvements, but nothing about that static member changed.
but unexpectedly I got this linker error message:
LNK2005 "private: static class GraphicsApp * GraphicsApp::self" (?self#GraphicsApp##0PEAV1#EA) already defined in main.obj.
LNK1169 one or more multiply defined symbols found.
So, I separated this header into .h and .cpp:
/* graphics_app.cpp */
#include "graphics_app.h"
...
GraphicsApp* GraphicsApp::self = nullptr;
but I got another error:
LNK2001 "private: static class GraphicsApp * GraphicsApp::self" (?self#GraphicsApp##0PEAV1#EA) unresolved external symbol.
LNK1120 1 unresolved externals.
Why these weird behavior happens & how can I fix?
EDIT:
I made test version to make problem simper.
This thing happens when I use my custom include directory...
such as
#include <dk/graphics_app.h>
instead of
#include "graphics_app.h"
So.. a new problem is, how can I fix this whilst using my custom include directory?
Edit2:
To make Thing much simpler..
LNK2005:
This error happened because, the header file was included in two other cpp files (compiled to obj files) . Then when the linker tried to link the obj it found two of the same definitions. But "there can be only one"!
Because of this ambiguity the linker gives up.
LNK2001:
This error happened because the linker did not find the defined variable in any obj file. So I think that the new cpp is missing from your project definition.
This header used to work... and I made some improvements, but nothing about that static member changed.
Your header is written incorrectly: you are not supposed to put definitions of entities with external linkage into header files. It could "work" as long as you included your header file into one and only one translation unit. But once you include it into two or more different translation units, you get the "multiple definition" error. Which is exactly what happened in your case.
So, I separated this header into .h and .cpp
This is the right thing to do. Now you have to make sure your graphics_app.cpp is compiled (and linked) as part of your program. This is something you forgot to do. The compiler/linker/build system cannot somehow "magically" realize by itself that your freshly created graphics_app.cpp is supposed to be part of your project.
I am having "unresolved external symbol" linking error for a simple class i wrote along with a header file in VS 2008 using c++.
I moved this class to VS 2008's include directory, so that I don't have to copy the files from one project to other every time creating a new project.
I included the header file in some new project, the file got included alright, I can also see the list functions and data members inside the object of that class file, [ VS 2008 shows me this list after I type '.' ]
But this is not the weird part, the weird part is, the files which I moved to include directory works fine in the original project in which I wrote them.
As well as including the header file in your new project, you will need to add the implementing cpp file, otherwise you will get
"unresolved external symbol"
link errors.
to understand "unresolved external symbol" issue please refer to:
Unresolved external symbol in object files
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.