I am trying to create a simple c++ project in Visual studio 2015
Peakdetector.h
#ifndef PEAKDETECTOR_H
#define PEAKDETECTOR_H
//-------------------------------------------------------
#ifdef DLL_BUILD_SETUP
#ifdef Q_OS_LINUX
#define DLLSPEC __attribute__((visibility("default")))
#else
#define DLLSPEC __declspec(dllexport)
#endif
#else
#ifdef Q_OS_LINUX
#define DLLSPEC
#else
#define DLLSPEC __declspec(dllimport)
#endif
#endif
namespace vpg {
#ifndef VPG_BUILD_FROM_SOURCE
class DLLSPEC PeakDetector
#else
class PeakDetector
#endif
private:
int __seek(int d) const;
double __getDuration(int start, int stop);
}
inline int PeakDetector::__seek(int d) const
{
return ((m_intervalslength + (d % m_intervalslength)) % m_intervalslength);
}
#endif
PeakDetector.cpp
#include "stdafx.h"
#include "peakdetector.h"
namespace vpg {
void PeakDetector::__updateInterval(double _duration)
{
//other stuff
}
}
When I try to run this application i get error
LNK2019 unresolved external symbol "__declspec(dllimport) private: int __cdecl vpg::PeakDetector::__seek(int)const " (__imp_?__seek#PeakDetector#vpg##AEBAHH#Z) referenced in function "private: void __cdecl vpg::PeakDetector::__updateInterval(double)" (?__updateInterval#PeakDetector#vpg##AEAAXN#Z) MyCustomProject
I am new to this and cannot figure out why am I having this error.I have just copy pasted this code from an example.Please let me know if I am missing any code. Also I dont have any .lib files.
You must add the DLL_BUILD_SETUP the defines in Visual Studio.
In order to do that, yo must go to
Project Settings -> C/C++ -> Preprocessor -> Preprocessor definitions
and add the definition to the list.
You must use the spec __declspec(dllexport) when compiling the library that is exporting the symbols (in this case the class), and __declspec(dllimport) in the project that USES that library.
I see from the source code that you've provided that there is an additional definition VPG_BUILD_FROM_SOURCE which disables the export in order to using static/inline linking, you may try to add that define instead.
Related
Basically I have a dll project in visual studio. I'm linking this dll project to a second project successfully but as soon as I try to use extern variables things go wrong. I've seperated my extern variables into a single header and source file from everything else so I can isolate the problem and potential solutions. I've scowered the internet for hours now and I feel like I've tried everything. I am beginning to think it might be a compile flag? Anyway, heres my code.
macros.h
#pragma once
// dll management
#ifdef TOAST_EXPORT
#ifdef _MSC_VER
#define TAPI __declspec(dllexport)
#else
#define TAPI __attribute__((visibility("default")))
#endif
#else
#ifdef _MSC_VER
#define TAPI __declspec(dllimport)
#else
#define TAPI
#endif
#endif
globals.h
#pragma once
#define TOAST_EXPORT
#include "macros.h"
namespace toast
{
TAPI extern const char c;
}
globals.c
Note that I tried this without const and made no assignment here
#pragma once
#include "globals.h"
namespace toast
{
const char c = 'a';
}
main.c (from the project that compiles to an exe)
#include <globals.h>
int main()
{
char c = toast::c;
return 0;
}
So far I've tried making a lot of subtle changes like reordering extern and const and such. I've also done it both with just extern and just const. Still produces the same unresolved external symbol "char const toast::c" error. Keep in mind that I can create instances of classes and call their methods from the dll successfully and thats with things like class TAPI logger... and such.
I have a Visual C++ solution, using Visual Studio 2017, which contains 5 projects:
SpikeConfig
SpikeEngine
SpikeRenderer
SpikeUI
SpikeUtils
In SpikeUtils, I have a header _SpikeEngineObject.h:
#pragma once
#ifdef DLL_SPIKEUTILS
#define SPIKEUTILS_EXPORT __declspec(dllexport)
#else
#define SPIKEUTILS_EXPORT __declspec(dllimport)
#endif
#include "GUID.h"
namespace SpikeUtils
{
class SPIKEUTILS_EXPORT _SpikeEngineObject
{
public:
const std::string & _SpikeEngineId()
{
return _SpikeRef.Value();
}
private:
SpikeUtils::GUID _SpikeRef = SpikeUtils::GUID::Generate();
};
}
The file GUID.h included looks like this:
#pragma once
#include <iostream>
#ifdef DLL_SPIKEUTILS
#define SPIKEUTILS_EXPORT __declspec(dllexport)
#else
#define SPIKEUTILS_EXPORT __declspec(dllimport)
#endif
namespace SpikeUtils
{
class SPIKEUTILS_EXPORT GUID final
{
public:
GUID(GUID const & other) = default;
GUID& operator=(GUID& other) = default;
static GUID Generate();
std::string const & Value();
private:
GUID(std::string const & value) : value(value)
{}
std::string value;
};
}
I am omitting the implementation of GUID.cpp because I don't think it's relevant.
Now, in SpikeUI, I have a class Drawable, that just inherits from _SpikeEngineObject.h
#pragma once
#include "_SpikeEngineObject.h"
#ifdef DLL_SPIKEUI
#define SPIKEUI_EXPORT __declspec(dllexport)
#else
#define SPIKEUI_EXPORT __declspec(dllimport)
#endif
namespace SpikeUI
{
namespace UI
{
struct SPIKEUI_EXPORT Drawable : SpikeUtils::_SpikeEngineObject
{
....
};
}
}
Obviously, all the respective DLL_ defines have been put inside each individual project's C/C++ -> Preprocessor -> Preprocessor definitions, so the projects should build with the appropriate dllimport / dllexport macro.
But when I try and build SpikeUI, I get linker errors like:
LNK2019 unresolved external symbol "__declspec(dllimport) public: __cdecl
SpikeUtils::_SpikeEngineObject::_SpikeEngineObject(void)" (__imp_??
0_SpikeEngineObject#SpikeUtils##QEAA#XZ) referenced in function "public:
__cdecl SpikeUI::UI::Drawable::Drawable(enum SpikeUI::UI::DrawableType)" (??
0Drawable#UI#SpikeUI##QEAA#W4DrawableType#12##Z)
and
LNK2019 unresolved external symbol "__declspec(dllimport) public: __cdecl
SpikeUtils::_SpikeEngineObject::~_SpikeEngineObject(void)" (__imp_??
1_SpikeEngineObject#SpikeUtils##QEAA#XZ) referenced in function "int
`public: __cdecl SpikeUI::UI::Drawable::Drawable(struct UI::Drawable::dtor$0
const &)'::`1'::dtor$0" (?dtor$0#?0???0Drawable#UI#SpikeUI##QEAA#AEBU012##Z#4HA)
An interesting fact is that Visual Studio even highlights which macro will be used, and for example GUID.h does highlight the dllexport macro, but _SpikeEngineObject.h highlights the dllimport macro for some reason.
Searching through SO and MSDN, it looks like this macro pattern should work, but for some reason it's not consistent on my project.
How can I solve the linker errors?
Answering my own question here:
The SpikeUI project has a dependency on the SpikeUtils project, and it is linked against the .lib and .dll project that is outputed by building the SpikeUtils project.
Now, the problem was that the class _SpikeEngineObject was a header-only class (ie no .cpp for the class). Hence, I am assuming that the SpikeUtils.lib did not contain any symbols for the constructor / destructor etc. of the _SpikeEngineObject, so the linker was having problems linking it.
I solved the problem by adding a .cpp file for the class and implementing dumb constructor / destructor so that the compiler would generate these symbols, and everything was fine.
I implement a C++ function as DLL with vs2013. But I have linker error (error LNK2019: unresolved external symbol _main referenced in function ___tmainCRTStartup) building to the dll. I have proper setup and not sure what is wrong. The code is very simple, but I don't know why it can't be built successfully.
Demoone.h
#ifndef _Demo_H_
#define _Demo_H_
#ifdef LIBDLL
#define LIBDLL extern "C" _declspec(dllimport)
#else
#define LIBDLL extern "C" _declspec(dllexport)
#endif
LIBDLL int Add(int plus1, int plus2);
#endif
Demoone.cpp
#include "Demoone.h"
int Add(int a, int b)
{
return (a + b);
}
update：
I modified the header file as bellow
#ifndef _Demo_H_
#define _Demo_H_
extern "C" int Add (int a , int b);
#endif
and add an def file
LIBRARY "Dllmaketwo"
EXPORTS
Add # 1
The same linker error (error LNK2019: unresolved external symbol _main referenced in function ___tmainCRTStartup) also appeared.
If you want to use load-time linking in the project that uses the DLL you need to link against the .lib produced by the DLL project build.
You can do that with:
#pragma comment(lib, "dllproject.lib")
Or by adding the .lib to the additional dependencies line in the project settings under Linker->Input. You may also need to mess with the library search path, either in the VC++ Directories page or in the Linker->General page.
#ifndef _Demo_H_
#define _Demo_H_
#ifdef LIBDLLIMPORT //Changed here
#define LIBDLL extern "C" _declspec(dllimport)
#else
#define LIBDLL extern "C" _declspec(dllexport)
#endif
LIBDLL int Add(int plus1, int plus2);
#endif
You should not use a same name in #ifdef and #define,
Did you setup you project correctly? And you should not write a `main()' function in it.
Just started doing some coding for a very simple automated test framework for internal use. (I know there are hundreds of them out there - really good ones too, but at the moment that's not interesting, so don't point me to any of those, please ;)) I then came across the following problem which I can't explain, thus asking for your help.
I have the following code as part of a DLL:
(The code is barely an embryo and took me <2 minutes to write, so it's logic, structure - nothing - is refined, in any way yet.)
h-file:
#pragma once
#ifdef __DLL__ // Defined in DLL-project
#define DLLEXPORT __declspec( dllexport )
#else
#define DLLEXPORT
#endif
class DLLEXPORT AutoTest
{
public:
enum eTestID {TESTID_SomeFunction};
AutoTest(eTestID id, LPVOID lpData)
{
if(sm_bTestsActive)
ExecTest(id, lpData);
}
void ActivateTests();
private:
static void ExecTest(eTestID id, LPVOID lpData)
{
}
static BOOL sm_bTestsActive;
};
cpp-file:
#include "StdAfx.h"
#include "AutoTest.hpp"
BOOL AutoTest::sm_bTestsActive = FALSE;
void AutoTest::ActivateTests()
{
sm_bTestsActive=TRUE;
}
This compiles just fine and the DLL gets generated.
Here's my problem though - when instantiating the class with:
AutoTest(AutoTest::TESTID_SomeFunction, &SomeData);
from the main application, the linker fails with
error LNK2001: unresolved external symbol "private: static int AutoTest::sm_bTestsActive" (?sm_bTestsActive#AutoTest##0HA)
<2 minutes to write - now going on 5 hours to understand why it fails!!! :O
Here's what interesting - if I move the constructor to the cpp-file (not inlined) it works just fine!?!?
Here's that code:
h-file:
#pragma once
#ifdef __DLL__ // Defined in DLL-project
#define DLLEXPORT __declspec( dllexport )
#else
#define DLLEXPORT
#endif
class DLLEXPORT AutoTest
{
public:
enum eTestID {FK3059};
AutoTest(eTestID id, LPVOID lpData);
void ActivateTests();
private:
static void ExecTest(eTestID id, LPVOID lpData)
{
}
static BOOL sm_bTestsActive;
};
cpp-file:
#include "StdAfx.h"
#include "AutoTest.hpp"
BOOL AutoTest::sm_bTestsActive = FALSE;
AutoTest::AutoTest(eTestID id, LPVOID lpData)
{
if(sm_bTestsActive)
ExecTest(id, lpData);
}
void AutoTest::ActivateTests()
{
sm_bTestsActive=TRUE;
}
(I've made some minor edits in the code after pasting, so there may or may not be simple syntax errors.)
Also, if I remove the reference to the static member from the inline versions constructor, it works fine.
Any ideas as to why the inline version won't work?
Pay attention to your definition of DLLEXPORT.
Make sure that it is properly expanded to __declspec(dllexport) when building the DLL, or __declspec(dllimport) when building the client.
I'd suggest using a macro with a more specific name than the generic DLLEXPORT (to avoid conflicts with other macros with the same name).
Having static data members accessed from inline member functions works fine for me (tested with VS2013).
Minimal repro:
Create a Visual Studio solution with an empty DLL project and an empty console application project.
Inside the DLL project add two files:
DllClass.h:
#pragma once
#ifndef TEST_DLL_CLASS
#define TEST_DLL_CLASS __declspec(dllimport)
#endif
class TEST_DLL_CLASS DllClass
{
public:
DllClass();
int GetMember() const
{
return m_data1;
}
static int GetStaticMember()
{
return sm_data2;
}
private:
int m_data1;
static int sm_data2;
};
DllClass.cpp:
#define TEST_DLL_CLASS __declspec(dllexport)
#include "DllClass.h"
int DllClass::sm_data2 = 2;
DllClass::DllClass()
: m_data1(1)
{
}
Inside the console app project, add one file:
Test.cpp:
#include "..\DllTestClass\DllClass.h"
#include <iostream>
using namespace std;
#pragma comment(lib, "DllTestClass")
int main()
{
DllClass dllClass;
cout << dllClass.GetMember() << endl;
cout << DllClass::GetStaticMember() << endl;
}
Make sure that when building the console test app, the linker can find the DLL .lib (DllTestClass.lib) file.
For that purpose, you can navigate the console app's project properties, going to:
Project Properties | Linker | Additional Library Directories
and add $(OutDir) to the additional library directories, making it:
$(OutDir);%(AdditionalLibraryDirectories)
Builds and works correctly for me.
Should be:
#ifdef __DLL__ // Defined in DLL-project
#define DLLEXPORT __declspec( dllexport )
#else
#define DLLEXPORT __declspec( dllimport )
#endif
You can declare C++ classes with the dllimport or dllexport attribute. These forms imply that the entire class is imported or exported. Classes exported this way are called exportable classes.
More information in the documentation.
I created a DLL project and successfully built it. I then tried to use the DLL in another Project, TEST, and I am getting the following error.
Error 1 error LNK2001: unresolved external symbol "public: void __thiscall SnoMessage::setRawMessageName(class ATL::CStringT<wchar_t,class StrTraitMFC_DLL<wchar_t,class ATL::ChTraitsCRT<wchar_t> > >)" (?setRawMessageName#SnoMessage##QAEXV?$CStringT#_WV?$StrTraitMFC_DLL#_WV?$ChTraitsCRT#_W#ATL#####ATL###Z)
I added the required lib in the linker properties, and I also added the header files in the TEST include directory. So the function is being recognized, but it keeps giving those errors. The DLL is comprised of the following files
SnoMessage.h
#pragma once
#include "StdAfx.h"
class SnoMessage
{
public:
__declspec(dllexport) SnoMessage(void);
__declspec(dllexport) ~SnoMessage(void);
__declspec(dllexport) void setRawMessageName(CString messageName);
__declspec(dllexport) void setRawMessageType(CString messageType);
__declspec(dllexport) void setRawMessageAttributes(std::map<CString,CString> attributes);
__declspec(dllexport) CString getRawMessageName();
__declspec(dllexport) CString getRawMessageType();
__declspec(dllexport) std::map<CString,CString> getRawMessageAttributes();
private:
CString messageName;
CString messageType;
std::map<CString,CString> attributes;
};
SnoMessage.cpp
#include "stdafx.h"
#include "SnoMessage.h"
SnoMessage::SnoMessage(void)
{
}
SnoMessage::~SnoMessage(void)
{
}
void SnoMessage::setRawMessageName(CString messageName){
this->messageName = messageName;
}
void SnoMessage::setRawMessageType(CString messageType){
this->messageType = messageType;
}
void SnoMessage::setRawMessageAttributes(std::map<CString,CString> attributes){
this->attributes = attributes;
}
CString SnoMessage::getRawMessageName(){
return messageName;
}
CString SnoMessage::getRawMessageType(){
return messageType;
}
std::map<CString,CString> SnoMessage::getRawMessageAttributes(){
return attributes;
}
And in test I am doing the following:
test.cpp
// test.cpp : Defines the entry point for the console application.
//
#include "stdafx.h"
#include "SnoMessage.h"
int _tmain(int argc, _TCHAR* argv[])
{
SnoMessage *msg = new SnoMessage();
msg->setRawMessageName("TEST");
return 0;
}
Let me know if you need more info, thanks.
In your dll define this in some header you want to use for your export defs...
MyExports.h
#ifdef SNOMESSAGE_EXPORTS
#define SNOMESSAGE_API __declspec(dllexport)
#else
#define SNOMESSAGE_API __declspec(dllimport)
#endif
Now in your dll you just define SNOMESSAGE_EXPORTS, then when your dll is compiled your class and methods will be visible to the exe. But when you include those same headers in the exe the Macro will import them instead of export.
//In the DLL this is == to export, in the executable this is import. Problem solved.
class SNOMESSAGE_API SnoMessage
{
public:
//...
};
You no longer need to export each member, just the class.
I would mark the whole class as exported, not just its member functions. Also, following the advice of this conversation, you need to specify __declspec(dllecport) or __declspec(dllimport) based on whether you are including the header in the DLL or the code that uses the DLL; and define the guarding macro in the DLL project.
When you compile the DLL you should have __declspec(dllexport), but when you compile exe you should have __declspec(dllimport). The easiest way to do this is to have a #define somewhere that has different value when "in DLL" and "out of DLL". Also do export the whole class instead of individual methods.
There is a case when dll compile use C call but exe use standard call, the link in x64 has no problem, but when using win32 will show this link error 2001. For that situation just use C call for both dll and exe for win32 platform (https://learn.microsoft.com/en-us/cpp/error-messages/tool-errors/name-decoration?view=msvc-160).