I'm a newbee in C++,
I'm trying to make a library for my program, and I've got this problem.
I have a .h file for declaration member functions.
class Quaternion
//qua.h
{
private:
public:
inline static Quaternion M2Qua(Matrix&);
}
a matrix.h file for declaration matrix class. And an Qua.cpp file for the define function, and I want to link the M2Qua function in the qua.h file.
//Qua.cpp
Quaternion Quaternion::M2Qua(Matrix& R)
{
}
When I called the function in my main program, the compiler printed an error.
the error is:
LNK 2019: unresolved external symbol "public: static class Quaternion _cdecl Quaternion::M2Qua(class Matrix&)
I read some relevant topics but I can't figure out where exactly the problem is. I just suppose it relates to the static member, that I declared in qua.h file. I hope someone helps me. Thanks in advance.
Related
I am using SFML's audio libraries.
In my class I tried to have a private static variable that holds a SoundBuffer* as such:
static sf::SoundBuffer* breakBlockBuffer;
This gives a linker error when I try to build:
Chunk.obj : error LNK2001: unresolved external symbol "private: static class sf::SoundBuffer * Chunk::breakBlockBuffer" (?breakBlockBuffer#Chunk##0PAVSoundBuffer#sf##A)
myprogram.exe : fatal error LNK1120: 1 unresolved externals
However, if I declare it as an instance variable, it works:
sf::SoundBuffer* breakBlockBuffer;
This happens regardless of whether I dynamically link or statically link the libraries. It also persists in both SFML1.6 and SFML2.0.
I'm feeling that I might have made some silly mistake since I'm pretty rusty at C++, but the code looks like it should be ok to me.
If you declare a static variable in your class, you must also define it on your source file:
foo.hpp:
class foo
{
static int bar;
};
foo.cpp:
int foo::bar;
Looks like you didn't do it.
Well, I have been struggling with this for days now. I am writing a custom game DLL for CryENGINE from scratch, and I cannot even get the solution compile with one simple class (Game.cpp) and a precompiled header (StdAfx.h).
Both Game.cpp and StdAfx.cpp will compile perfectly on their own, but compiling the solution throw tons of multiply defined errors. The class is simple because the definitions are just placeholders.
Game.h
#if !defined __GAME__H__
#define __GAME__H__
#pragma once
class CGame : public IGame
{
public:
CGame();
VIRTUAL ~CGame();
//IMPLEMENT: IGame Interface, all methods declared.
};
#endif
Game.cpp
#include "StdAfx.h" //PreComp header
#include "Game.h"
//Define all methods, each one has a simple definition.
StdAfx.h
#if !defined __STDAFX__H__
#define __STDAFX__H__
#pragma once
//Various CryENGINE includes
#endif
Output
error LNK2005: "struct SSystemGlobalEnvironment * gEnv" (? gEnv##3PEAUSSystemGlobalEnvironment##EA) already defined in StdAfx.obj
error LNK2005: "public: static long volatile _CryMemoryManagerPoolHelper::allocatedMemory" (?allocatedMemory#_CryMemoryManagerPoolHelper##2JC) already defined in StdAfx.obj
error LNK2005: "public: static long volatile _CryMemoryManagerPoolHelper::freedMemory" (?freedMemory#_CryMemoryManagerPoolHelper##2JC) already defined in StdAfx.obj
error LNK2005: "public: static long volatile _CryMemoryManagerPoolHelper::requestedMemory" (?requestedMemory#_CryMemoryManagerPoolHelper##2JC) already defined in StdAfx.obj
error LNK2005: "public: static int volatile _CryMemoryManagerPoolHelper::numAllocations" (?numAllocations#_CryMemoryManagerPoolHelper##2HC) already defined in StdAfx.obj
The list goes on...
What really throws me off is that each one will compile just fine individually, so syntax and references are good. What could possibly cause multiply defined errors when the solution is compiled as a whole?
I really appreciate help on this frustrating issue, thank you.
I'm not sure the errors are caused by the precompiled header, but here is the correct way to set up the precompiled header:
Right-click on the project name in Solution Explorer, select Properties, go to Configuration Properties | C/C++ | Precompiled Headers and set the Precompiled Header setting to Use (/Yu). Leave the other two settings below it to the default.
Right-click on StdAfx.cpp, go to the same setting and set it to Create (/Yc).
Well, I figured it out. There is a clever complex include that does not belong in the precompiled header:
#include <Platform_Impl.h>
This was causing all my problems, and by moving it to Game.cpp, everything is fine.
I have C++ managed dll compiled with /clr that has some global functions.
for example
void Managed2UnManaged(DataStructures::AAA^ elem, DataStructures::CPP::AAA* copy_elem);
when I try to use these functions in a C++ managed console application I get the following errors
error LNK2028: unresolved token (0A00048C) "void __clrcall Managed2UnManaged(class DataStructures::AAA ^,class DataStructures::CPP::AAA *)" (?Managed2UnManaged##$$FYMXP$AAVAAA#DataStructures#NextIn##PAV1CPP#23##Z)
error LNK2019: unresolved external symbol "void __clrcall Managed2UnManaged(class DataStructures::AAA ^,class DataStructures::CPP::AAA *)" (?Managed2UnManaged##$$FYMXP$AAVAAA#DataStructures#NextIn##PAV1CPP#23##Z)
I added to the console application a reference to the dll but it still gives the error.
I also tried adding __declspec(dllexport) but then I get
error C3395: 'Managed2UnManaged' : __declspec(dllexport) cannot be applied to a function with the __clrcall calling convention
and if I specify __stdcall I get
error C4439: 'Managed2UnManaged' : function definition with a managed type in the signature must have a __clrcall calling convention
I am using VS2012.
the h file has
class XXX {
public:
static void Managed2UnManaged(DataStructures::RegResult^ elem, DataStructures::CPP::RegResult* copy_elem);
};
and the cpp file
void XXX::Managed2UnManaged(DataStructures::RegResult^ elem, DataStructures::CPP::RegResult* copy_elem)
{
}
Problem Solved. the problem was that I also needed to declare the class public ref. this caused a different problem because that the native c++ types are private. so I had to use the make_public pragma.
Thanks all.
I think that the problem may be that the CLR doesn't allow global functions.
You must create a managed class and write your function as a static member function of that class, for that function to be exported.
I have a dll which has an abstract class with all of its member functions are pure virtual functions. I am trying to write an application to call these functions. What are the steps I need to take to call these pure virtual functions?
This is a just a prototype
Header file with abstract class : interface.h [These are the exported functions]
class MathFuncExport {
public:
virtual int Add(int a, int b)=0;
MathFuncExport(){};
virtual ~MathFuncExport(){};
};
Header file in dll : MathFuncDll.h
#include "intf.h"
class MyMathFuncs : public MathFuncExport
{
public:
MyMathFuncs(){};
virtual ~MyMathFuncs(){};
virtual int Add(int a, int b);
};
Implementation : MyMathFunsDll.Cpp file
#include "MathFuncDll.h"
int MyMathFuncs::Add(int a, int b)
{
return a + b;
}
This created a dll but I am not able to call the functions in abstract class or I am missing some link here. Please help me in resolving this issue.
Thanks
You cannot call pure virtual. They are implemented to force function(s) implementation.
Since your base class is in the DLL you have to export class in order to use it for deriving other classes.
The easiest way to export class is to use implicit linking; this way you need a header for the class declaration and import library. For overllok of the different linkages check this link.
For a little demo create Win32 dll. Check MFC support if you need it and check the Export Symbols box.
This will create a dll with sample class and global variable export. Look at the header file where special macro is created, having different meaning for DLL (export) and executable linking with this dll (import).
Once you understand how to use implicit linking, you will be able to derive class from the base class in the dll as if you were using code in the executable module.
I have a unmanaged C++ dll for which I do not have access to code but have all methods declarations for.
Lets for simplicity say that .h looks like this:
#include <iostream>
#ifndef NUMERIC_LIBRARY
#define NUMERIC_LIBRARY
class Numeric
{
public:
Numeric();
int Add(int a, int b);
~Numeric();
};
#endif
and method implementation in .cpp file
int Numeric::Add(int a, int b)
{
return (a + b);
}
I simply want to call the add function from C++ in my C# code:
namespace UnmanagedTester
{
class Program
{
[DllImport(#"C:\CPP and CSharp Project\UnmanagedNumeric\Debug\numeric.dll", EntryPoint = "Add")]
public static extern int Add(int a, int b);
static void Main(string[] args)
{
int sum = Add(2, 3);
Console.WriteLine(sum);
}
}
}
After trying to execute I have the following error:
Unable to find an entry point named 'Add' in DLL 'C:\CPP and CSharp Project\UnmanagedNumeric\Debug\numeric.dll'.
I CAN NOT change C++ code. Have no idea what is going wrong.
Appreciate your help.
Using PInvoke you can only call global functions exported from Dll. To use exported C++ classes, you need to write C++/CLI wrapper. This is C++/CLI Class Library project, which exposes pure .NET interface, internally it is linked to unmanaged C++ Dll, instantiates a class from this Dll and calls its methods.
Edit: you can start from this: http://www.codeproject.com/KB/mcpp/quickcppcli.aspx#A8
If you need to create a wrapper, take a look at swig.org. It will generate one for most high level language like C#.
I just came across this program a few minutes ago while working the same problem that you are.
To use a class from native C++ from C# you need a C++/CLi wrapper in between, as mentioned by by previous answers. To actually do that, it is not very straight forward. Here is I link that tell you how to do it at a high level: C++/CLI wrapper for native C++ to use as reference in C#.
If you are quite new to this (like me), you might stumble on 1) -- the linking part. To solve that, you can see how I did here (see my question portion): Link error linking from managed to unmanaged C++ despite linking to .lib file with exported symbols