I have read this informative stackoverflow question regarding unresolved external symbols, but I am still not sure how to solve my issue.
Within Visual Studio 2012, I have a solution consisting of multiple projects, one of which is a static library called common. Each project that produces an executable consists of a header and associated cpp file of all global functions used throughout that specific program, called programglobals. In the process of developing one of these projects, I started duplicating some of this code from one project's programglobals to another. Now that I have completed all the projects, I want to extract the duplicate code into a associated header and cpp file within the common library, but I believe I might be referencing them incorrectly, which is producing these unresolved external symbol errors
Here is a dumbed down example of what I am currently attempting.
Common Library Files
//solutionglobals.h
void commonFunction();
//solutionglobals.cpp
void commonFunction() {
int asdf;
}
Project A Files
// programglobals.h
#include "../common/solutionglobals.h
void functionUsedInProjectA();
// programglobals.cpp
void functionUsedInProjectA() {
int x;
}
// output.h
#include "programglobals.h"
void asdfA();
// output.cpp
void asdfA() {
int x;
functionUsedInProjectA();
commonFunction();
}
Project B Files
// programglobals.h
#include "../common/solutionglobals.h
void functionUsedInProjectB();
// programglobals.cpp
void functionUsedInProjectB() {
int x;
}
// output.h
#include "programglobals.h"
void asdfB();
// output.cpp
void asdfB() {
int x;
functionUsedInProjectB();
commonFunction();
}
Any reference to commonFunction() results in an unresolved external symbol error.
Thanks!
You will have to specify in your executable projects that they reference the static lib. May be http://msdn.microsoft.com/en-us/library/vstudio/ms235627%28v=vs.110%29.aspx#uselibinapp helps (lower third of the article).
Before you can use the math routines in the static library, you must
reference it. To do this, open the shortcut menu for the MyExecRefsLib
project in Solution Explorer, and then choose References. In the
MyExecRefsLib Property Pages dialog box, expand the Common Properties
node, select Framework and References, and then choose the Add New
Reference button.
The linker cannot 'see' your function and as such thinks that it does not have an external symbol referencing it, hence the error.
You must #pragma comment(lib, [library here]) to reference the external function.
The following code can be used to reproduce this error:
[header file- test.h]:
#include "StdAfx.h"
void someOtherFunction();
void someFunction(string thisVar);
[code file- test.cpp]:
#include "StdAfx.h"
#include "test.h"
void someOtherFunction()
{
printf("Hello World!");
}
[function body for someFunction(string thisVar) is missing!]
Related
I have a Visual C++ solution with 2 projects: rectangle and project3.
In rectangle project I have rect.cpp and rect.h.
rect.h
#ifndef rect_h
#define rect_h
class Rect
{
public:
Rect();
int m_h;
int m_w;
};
#endif //rect_h
rect.cpp
#include "rect.h"
Rect::Rect()
{
m_h = 1;
m_w = 5;
}
whenever I try to create rect object from the rectangle project it succeeds.
But when I try to do the same from the project3 it produces a linker error.
LNK2019: unresolved external symbol "public: __thiscall
Rect::Rect(void)" (??0Rect##QAE#XZ) referenced in function _main
1>C:\Users\mbaro\documents\visual studio
2017\Projects\Project2\Debug\Project3.exe : fatal error LNK1120: 1
unresolved externals
main.cpp (in project 3)
#include "rect.h"
using namespace std;
int main()
{
Rect* a = new Rect();
return 0;
}
I kind of feel that class definition is picked up successfully, but the linker can not link the constructor code from rect.cpp.
What is the problem and how to solve it?
Thanks.
The error is normal: you told the compiler where it could find the .h files, but you did not tell the linker where it could find the .obj files.
It may depend on the exact VS version, but in Project/Properties, you should find Linker/Input and there Additional dependencies. If you only need one or two object files (xxx.obj) from the other project, add them here. That way, you avoid code duplication, which will be a nightmare for future maintenance...
If you have many common files, you should considere to put them in an auxilliary project that would build a (static)library in the same solution, and then link the library in both project (and of course give access to header files of the library project for the other projects using the library).
I have already started writing a long, long answer. Then i realized, what You may be missing is that despite Your class is named "Person" the header file You should have added is named "rect.h".
Also Your constructor cannot have a declaration of values in the header file (EDIT:not true, I was mistaken). In the header file, try using:
Person(int h, int w);
You declare what will be needed, not what You already have. If You want those to be specifically what You wrote the constructor should be:
Person();
in .h
and
Person::Person()
{
m_h = 1;
m_w = 5;
}
in .cpp.
If You need more detailed description of using include, I have already written a big part of it, so don't hesitate to ask.
For the life of me I cannot figure out what is causing this... I keep getting unresolved external symbol error. However, if I put an empty definition in the header file it compiles correctly.
WINMAIN.CPP
#include "FILE_XXX.H"
int WINMAIN WinMain(...)
{
EnableOpenTest(); // call like this
return 0;
}
FILE_WORKS_CORRECTLY.H
#ifndef _FILE_WORKS_CORRECTLY_
#define _FILE_WORKS_CORRECTLY_
void EnableOpenTest() { }
#endif
However, when I do something like this (correctly), it does not work and I get a compile-time error.
FILE_DOES_NOT_WORK_CORRECTLY.H
#ifndef _FILE_DOES_NOT_WORK_CORRECTLY_
#define _FILE_DOES_NOT_WORK_CORRECTLY_
void EnableOpenTest();
#endif
FILE_DOES_NOT_WORK_CORRECTLY.CPP
#include "FILE_DOES_NOT_WORK_CORRECTLY.H"
void EnableOpenTest() { /* do work here */ }
UPDATE:
Upon further investigation, I found the issue has to do with me having multiple projects in the same solution. I then try to reference a function in one project from another project. Obviously I'm doing this incorrectly.
The only mistake i see is that in the cpp file you need to include the return type as well. It should be
void EnableOpenTest()
{
//Enter Code Here
}
Inside of FILE_DOES_NOT_WORK_CORRECTLY.CPP:
EnableOpenTest(){ /* do work here */ }
must be
void EnableOpenTest(){ /* do work here */ }
Looks like your compiler sets the missing return type to int instead of yelling at you with a error message.
You should turn on compiler warnings, it would allow you to notice such errors very quickly.
Also, inside of FILE_WORKS_CORRECTLY.H you have another error:
void EnableOpenTest() { }
must be
inline void EnableOpenTest() { }
Otherwise it will trigger a error message if this header is included twice (i.e. in more that one .cpp file).
Solved it!
Additional projects needed to be static library (main project .exe)
Added References of library projects to main project
Obviously the file structure caused a lot of these issues.
EDIT: I know there are similar questions, but I cannot find an answer to a following issue: Why the methods inside the class are working correctly and outside are not.
I've got a weird problem in my project which I'm developing in MSVC++ 2012. My project consists of different modules of code. The important modules from the problem's point of view is a library and the GUI. They exist as different projects in the same solution.
I have some methods in the library which are part of the classes (in this case Calibration3D):
void Calibration3D::load(const std::string &path)
I use it without problems when I need it in the GUI, however I need to use a following method (outside the class):
void xxxyyy()
But when I'm trying to use that function (outside the class but in the same namespace) I get a following error:
1>project_xml.obj : error LNK2001: unresolved external symbol "void __cdecl cci::xxxyyy(void)" (?xxxyyy#cci##YAXXZ) 1>D:\praca_pw\cci\build-msvc2012\x64\Release\\ccigui.exe : fatal error LNK1120: 1 unresolved externals
Anybody knows how to solve it?
When I have a header file like this:
namespace xyz {
void foo();
class bar { ... };
}
then I write the cpp file like this:
#include "xyz.h"
namespace xyz {
void foo() { ... }
bar::bar() { ... }
}
This means I have to type a lot less and make fewer mistakes with regard to namespaces.
OK, solved, it seems that when a method is defined inside the namespace in header file, it should also be defined explicitly as part of namespace in implementation file, in this case:
cci::xxxyyy()
{
...
}
will work and
xxxyyy()
{
...
}
will not.
I face a very strange link problem with VC 2010. Now I am developing a C++ library, and in order to make debug much easier, for some functions the library provides two function interfaces. For example,
class Object
{
public:
int fun(std::vector<int> &auxiliary_variable_for_debug_purpose);
int fun();
}
It is also possible to reorganize this class in this way:
class Object
{
public:
#ifdef DEBUG_INDICATOR
int fun(std::vector<int> &auxiliary_variable_for_debug_purpose);
#else
int fun();
#endif
}
By doing so I except to give a clear interface to the user.
The problem I face now is both int fun(std::vector<int> &auxiliary_variable_for_debug_purpose); and int fun(); will invoke another function called void help_function(), which is declared and defined in separated files.
file.h
void help_function()
and
file.cpp
void help_function()
{
// do something
}
As you can see void help_function() is the same regardless whether DEBUG_INDICATOR is defined or not. If I defined DEBUG_INDICATOR, I can compile the class with int fun() function without any problem. However, when I undefined DEBUG_INDICATOR, the error LNK2001 error happens, suggesting unresolved external symbol void help_function(). I have tried every possible means to figure it out, but failed. Any ideas will be appreciated.
EDIT
The library I have built is a dynamic library. Regardless whether DEBUG_INDICATOR is defined, the library can be built, and the link error only happens when the library is invoked.
Since you've not posted the exact error message you are getting, this MSDN link might help you.
Tip: Be specific while asking your question if you wish to receive accurate answers.
I have 2 static libraries from «vendor1» and «vendor2»:
vendor1.lib and vendor1.h;
vendor2.lib and vendor2.h.
In the file, vendor1.h. The following declaration is there:
double Min();
In the file, vendor2.h. The following declaration is there:
double Min();
In my client file:
include "vendor1.h"
include "vendor2.h"
double x = Min();
It by defaults calls vendor1.h. I tried introducing the namespace:
namespace vendor1 {
include "vendor1.h"
}
namespace vendor2 {
include "vendor2.h"
}
A call to the following function
double xx = vendor2::Min();
I get the following linker errors:
Client.cpp 1>Client.obj : error LNK2019: unresolved external symbol "double __cdecl vendor2::Min(void)" (?Min#vendor2##YANXZ) referenced
in function _wmain 1>c:\temp\Client\Debug\Client.exe : fatal error
LNK1120: 1 unresolved externals
How can I fix this without creating wrappers for each of the wrappers?
If you have two static libraries with conflicting names you won't be able to link your program statically! The static linker will just go and find the first symbol matching an undefined symbol and choose this. Wrapping the names into a namespace doesn't help: this changes the namespace being expected in the library. You just found why namespace are a good thing.
How to solve the problem? I'm not aware of an approach which is based on the C++ standard. Practically, you may be able to do something: create a dynamic library which forwards to your conflicting functions but puts the name into separate namespaces (or uses different names). The dynamic libraries are linked with individual static libraries, i.e. the conflict doesn't happen at this time. You will probably also need to avoid the underlying names being visible from the symbols in the shared library. The details on how this is done depend on the compiler and I don't know who to deal with MSVC++ for things like this.
How about wrapping the functions into different namespaces?
vendor1_wrapper.h:
namespace vendor1 {
double Min();
}
vendor1_wrapper.cpp:
#include "vendor1_wrapper.h"
#include "vendor1.h"
namespace vendor1 {
double Min()
{
return Min();
}
}
vendor2_wrapper.h:
namespace vendor2 {
double Min();
}
vendor2_wrapper.cpp:
#include "vendor2_wrapper.h"
#include "vendor2.h"
namespace vendor2 {
double Min()
{
return Min();
}
}
Now you can use the functions using namespaces (your client file):
#include "vendor1_wrapper.h"
#include "vendor2_wrapper.h"
...
vendor1::Min();
vendor2::Min();