I want to debug a DLL.
This DLL exports some functions and voids:
This is the header:
#ifdef CODEC_EXPORTS
#define CODEC_API __declspec(dllexport)
#else
#define CODEC_API __declspec(dllimport)
#endif
extern "C" CODEC_API int __stdcall SpxInit(void);
extern "C" CODEC_API int __stdcall SpxEncode(unsigned char* inBuf, unsigned char* outBuf, unsigned int inlen);
extern "C" CODEC_API int __stdcall SpxEncodeNormal(void);
extern "C" CODEC_API int __stdcall SpxDecode(unsigned char* DinBuf, float* DoutBuf, unsigned int Dinlen);
extern "C" CODEC_API int __stdcall SpxFree(void);
#pragma comment(linker, "/export:SpxEncode=_SpxEncode#12")
#pragma comment(linker, "/export:SpxEncodeNormal=_SpxEncodeNormal#0")
#pragma comment(linker, "/export:SpxDecode=_SpxDecode#12")
#pragma comment(linker, "/export:SpxInit=_SpxInit#0")
#pragma comment(linker, "/export:SpxFree=_SpxFree#0")
I added a new project to my solution and simply added the following cpp file:
#include "stdafx.h"
#include "codec.h"
int _tmain(int argc, _TCHAR* argv[])
{
return 0;
}
Now before trying anything else, I simply wanted to compile the new project, but VC2010 is telling me
"error LNK2001" Unresolved external symbol "_SpxDecode#12"
"error LNK2001" Unresolved external symbol "_SpxEncode#12"
etc...
So I guess I missed something, but I don't see what.
You need to add reference to your dll project
Project properties->Common Properties->References
Related
I am trying out a simple test DLL project. Under my solution, I have two projects - first C++ Dll (library) and second C++ exe (driver). Below I've attached a snapshot of the basic project setup:
dllmain.h
#ifndef DLLMAIN_H_
#define DLLMAIN_H_
#ifdef FFMPEGLIB_EXPORTS
#define FFMPEGLIB_API __declspec(dllexport)
#else
#define FFMPEGLIB_API __declspec(dllimport)
#endif // FFMPEGLIB_EXPORTS
static void TestFoo();
extern "C" FFMPEGLIB_API void Test(int* num);
extern "C" FFMPEGLIB_API void ProxyFoo();
#endif
dllmain.cpp
#include "dllmain.h"
#include "A.h"
void TestFoo()
{
A a;
a.foo();
}
void Test(int* num)
{
*num = *num + 1;
}
void ProxyFoo()
{
TestFoo();
}
driver.cpp
#include <iostream>
#include "dllmain.h"
int main(int argc, char** argv)
{
int mum = 4;
Test(&num);
std::cout << num;
ProxyFoo();
return 0;
}
The library project compiles normally, but the exe fails to compile with a linker error:
Code Description Project File
LNK2001 unresolved extern symbol _imp_ProxyFoo driver driver.obj
LNK2001 unresolved extern symbol _imp_Test driver driver.obj
LNK1120 2 unresolved externals driver driver.exe
I have two questions here:
Why does the function name of dllmain.h get mangled in spite of being marked as extern "C"?
Why can I not create an instance of test class A from extern methods? What would be a good way of doing that?
Why the function name of dllmain.h getting mangled in spite being
marked as extern "C"?
Because __declspec(dllimport).
Why can I not create instance of test class A from extern methods?
What would be good way of doing it?
I think that's fine, but you didn't provide any class A code. Just do this:
class __declspec(dllexport) A
{
/* ... */
};
Why EXE compile failed?
This is because you have not imported the LIB file of the DLL into the project.
There are two ways to import it:
Add #program comment(lib, "<YOUR_LIB_FILE>.lib") to the code file.
Add <YOUR_LIB_FILE>.lib to Properties -> Linker -> Input -> Additional Dependencies.
Microsoft documentation: https://learn.microsoft.com/en-us/cpp/build/importing-and-exporting
You need to put the extern "C" thing around your function definitions that you intend to export in dllmain.cpp so it matches the linkage of your declaration.
Also, you need to do the declexport thing too.
extern "C"
{
__declspec(dllexport) void Test(int* num)
{
*num = *num + 1;
}
__declspec(dllexport) void ProxyFoo()
{
TestFoo();
}
}
I'm learning how to build a DLL and call it from another project(I also want the DLL can be called not only by C/C++ but also by Python). Here is my code for building the DLL:
callbacktesetDLL.h:
#ifdef CALLBACKTESTDLL_EXPORTS
#define CALLBACKTESTDLL_API __declspec(dllexport)
#else
#define CALLBACKTESTDLL_API __declspec(dllimport)
#endif
typedef int(CALLBACK *p)(char*);
CALLBACKTESTDLL_API int __stdcall StrToInt(char*);
CALLBACKTESTDLL_API char* __stdcall NumCompare(p FuncP, char*, int b);
callbacktestDLL.cpp:
#include "stdafx.h"
#include <stdio.h>
#include "callbacktestDLL.h"
#include <stdlib.h>
CALLBACKTESTDLL_API int __stdcall StrToInt(char* StrInput)
{
int IntResult;
IntResult = atoi(StrInput);
return IntResult;
}
CALLBACKTESTDLL_API char* __stdcall NumCompare(p FuncP, char* StrInput, int b)
{
int a = FuncP(StrInput);
if (a>b)
{
return "a is bigger than b";
}
else
{
return "b is bigger than a";
}
}
And a Source.def file:
LIBRARY
EXPORTS
StrToInt #1
NumCompare #2
With the code above, I got callbacktestDLL.dll and callbacktestDLL.lib. With depends, the functions' names in the DLL can be shown:
Now I want to call the functions in the DLL from another project:
CallDLL.h:
#pragma comment(lib,"callbacktestDLL.lib")
#include "targetver.h"
#include <stdio.h>
#include <tchar.h>
typedef int(*p)(char*);
extern "C" _declspec(dllimport) int StrToInt(char* InpuString);
extern "C" _declspec(dllimport) char* NumCompare(p FuncP, char*, int b);
CallDLL.cpp:
#include "stdafx.h"
int main()
{
p FuncP_R = StrToInt;
NumCompare(FuncP_R, "1234", 40);
return 0;
}
However, when I run the project, it told me:error LNK2019: unresolved external symbol __imp__StrToInt and error LNK2019: unresolved external symbol __imp__NumCompare. I've already copy the .lib and .dll files under the CallDLL project's root folder. Why this happens? How can I solve it? Thank you for your attention.
I finally made it. Here is the details:
The files that generate the DLL:
callbacktestDLL.h:
typedef int(CALLBACK *p)(char*);
extern "C" __declspec(dllexport) int __stdcall StrToInt(char* InputString);
extern "C" __declspec(dllexport) char* __stdcall NumCompare(p FuncP, char* InputString, int b);
callbacktestDLL.cpp:
#include "stdafx.h"
#include <stdio.h>
#include "callbacktestDLL.h"
#include <stdlib.h>
extern "C" CALLBACKTESTDLL_API int __stdcall StrToInt(char* InputString)
{
int IntResult;
IntResult = atoi(InputString);
return IntResult;
}
extern "C" __declspec(dllexport) char* __stdcall NumCompare(p FuncP, char* InputString, int b)
{
int a = FuncP(InputString);
if (a>b)
{
return "a is bigger than b\n";
}
else
{
return "b is bigger than a\n";
}
}
Comparing to the former files in the post, I removed the .def file and added extern "C" ahead of each function declaration and definition. Then I generate a new .dll and .lib files and copy them to the CallDLL projects' root folder. I used depends to see the functions' names in the DLL:
I also changed the CallDLL's file like this:
CallDLL.h:
#pragma comment(lib,"callbacktestDLL")
#include "targetver.h"
#include <stdio.h>
#include <tchar.h>
typedef int(__stdcall *p)(char*); //same as typedef int(CALLBACK *p)(char*) in callbacktestDLL.h
extern "C" _declspec(dllimport) int __stdcall StrToInt(char* InputString); //exactly same as what's in callbacktestDLL.h apart from dllimport
extern "C" _declspec(dllimport) char* __stdcall NumCompare(p FuncP, char* InputString, int b); //exactly same as what's in callbacktestDLL.h apart from dllimport
CallDLL.cpp:
#include "stdafx.h"
int main()
{
p FuncP_R;
char* a = "1234";
FuncP_R = StrToInt;
printf(NumCompare(FuncP_R, a, 42));
return 0;
}
It worked as expected. I think one of the mistakes I made is missing __stdcall when importing. Maybe there are also mistakes about the name mangling. I'll keep testing it.
You should always include the same header file to define a consistent interface. Creating different header files is error prone. The next change to the interface might make the interface incompatible.
There is a slight difference between the module that implements the functions to the module that uses the functions. The difference is the __declspec(dllimport) or __declspec(dllexport). That's why the header files contains the
# ifdef CALLBACKTESTDLL_EXPORTS
Your module that implements the functions also export them. Therefore you must defined the symbols in the project settings. If you compile at the command line you have to add the /D CALLBACKTESTDLL_EXPORT to the compiler arguments.
BTW: If you have defined CALLBACKTESTDLL_EXPORT your macro CALLBACKTESTDLL_API contains the __declspec(dllexport). This causes the linker to create the DLL export table. The .DEF is not necessary. You should remove it because..... it defines the interface again (at a different level).
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.
I can`t export an array from a DLL. Here is my code:
" DLL header "
#ifdef EXPORT
#define MYLIB __declspec(dllexport)
#else
#define MYLIB
#endif
extern "C" {
/* Allows to use file both with Visual studio and with Qt*/
#ifdef __cplusplus
MYLIB double MySum(double num1, double num2);
extern MYLIB char ImplicitDLLName[];
#else
extern Q_DECL_IMPORT char ImplicitDLLName[];
Q_DECL_IMPORT double MySum(double num1, double num2);
#endif
}
" DLL source"
#define EXPORT
#include "MySUMoperator.h"
double MySum(double num1, double num2)
{
return num1 + num2;
}
char ImplicitDLLName[] = "MySUMOperator";
" client main.cpp"
int main(int argc, char** argv)
{
printf("%s", ImplicitDLLName);
}
When building I am getting from the linker this error:
Error 2 error LNK2001: unresolved external symbol _ImplicitDLLName \Client\main.obj
// My purpose of exporting the array is to study export of different data structs from DLLs
How to cope with the error raised by linker and what rules are violated?
*UPDATE: *
IDE Visual Studio 2010.
Client - is written on C++, also DLL is on C++
Assuming you're linking your import library correctly (and thats a big assumption), you're not declaring MYLIB correctly for importing symbols:
This:
#ifdef EXPORT
#define MYLIB __declspec(dllexport)
#else
#define MYLIB
#endif
Should be this:
#ifdef EXPORT
#define MYLIB __declspec(dllexport)
#else
#define MYLIB __declspec(dllimport)
#endif
Keep in mind we've little context to work with. It looks like you're trying to consume this from a C-compiled application, but without more info I can't be sure. If that is the case, then Q_DECL_IMPORT had better do the above or it still will not work. I'd start with a basic "C" linkage export and work your way up from there.
Sample EXPORTS.DLL
Exports.h
#ifdef EXPORTS_EXPORTS
#define EXPORTS_API __declspec(dllexport)
#else
#define EXPORTS_API __declspec(dllimport)
#endif
extern "C" EXPORTS_API char szExported[];
Exports.cpp
#include "stdafx.h"
#include "Exports.h"
// This is an example of an exported variable
EXPORTS_API char szExported[] = "Exported from our DLL";
Sample EXPORTSCLIENT.EXE
ExportsClient.cpp
#include "stdafx.h"
#include <iostream>
#include "Exports.h"
using namespace std;
int _tmain(int argc, _TCHAR* argv[])
{
cout << szExported << endl;
return 0;
}
Output
Exported from our DLL
This must be a basic question but I am struggling with this problem for too long now.
I've looked everywhere on Google and found some similar problems and solutions but none that solved my specific problem.
I've written a very basic C++ DLL. In fact it is almost in C style because the DLL only has a main.cpp code file with a function in it so it's not even using a class.
Then I have two header files :
MqlUtils.h :
#ifndef MQLUTILS_H
#define MQLUTILS_H
struct MqlStr
{
int len;
char *string;
};
enum TradeOperation
{
OP_BUY = 0,
OP_SELL = 1,
OP_BUYLIMIT = 2,
OP_SELLLIMIT = 3,
OP_BUYSTOP = 4,
OP_SELLSTOP = 5
};
#endif
main.h :
#ifndef _DLL_H_
#define _DLL_H_
#include "MqlUtils.h"
#define MT4_EXPFUNC __declspec(dllexport)
#define export extern "C" __declspec( dllexport )
MT4_EXPFUNC int __stdcall GetOrdersDetailsNoSymbol(const int orderCount, const char * MasterLicense, const char * SlaveLicense, int orderTicket[], int op[],
double orderOpenPrice[], double orderStoploss[],
double orderTakeProfit[], double orderLots[], int orderDateTime[],
MqlStr * ordersymbol, MqlStr * ordercomments, int lotsCopyingMethod[], int returnedOrders[]);
#endif /* _DLL_H_ */
In fact, for creating my DLL, I started with existing code that someone else wrote, so the .cpp file for my DLL has some obscure syntax that I am not even sure what it is doing. Here's an excerpt of what the .cpp looks like :
#include "main.h"
#define _UNICODE 1
#define UNICODE 1
#define WIN32_LEAN_AND_MEAN
// ...
EXTERN_C IMAGE_DOS_HEADER __ImageBase;
#if BUILDING_DLL
#define DLLIMPORT __declspec (dllexport)
#else /* Not BUILDING_DLL */
#define DLLIMPORT __declspec (dllimport)
#endif /* Not BUILDING_DLL */
// ...
#ifdef __cplusplus
extern "C"
{
#endif
// ... function code
#ifdef __cplusplus
}
#endif
I did not include everything that is in the .cpp file, where there are // ... there is something else but it's basic stuff that I understand well so it shouldn't be the source of my problem...I'll be glad to post more as needed.
I am not an expert with all the obscure keywords like __declspec and such, but the DLL as it is, can be succesfully imported and the function GetOrdersDetailsNoSymbol can be used by some program, namely MetaTrader 4 (which is the main goal of my lib).
But now I would like to be able to test my library with a C++ program, so I created an empty console program, added the library project to the testing project's references and linked the .obj and .h files through the testing project's properties.
I am currently getting this when I compile the testing project :
Error 2 error LNK1120: 1 unresolved externals Z:\Codes\Debug\TestsCpp.exe TestsCpp
Error 1 error LNK2019: unresolved external symbol "__declspec(dllimport) int __cdecl GetOrdersDetailsNoSymbol(int,char *,char *,int * const,int * const,double * const,double * const,double * const,double * const,int * const,struct MqlStr *,struct MqlStr *,int * const,int * const)" (__imp_?GetOrdersDetailsNoSymbol##YAHHPAD0QAH1QAN2221PAUMqlStr##311#Z) referenced in function "void __cdecl TestClient(void)" (?TestClient##YAXXZ) Z:\Codes\TestsCpp\main.obj TestsCpp
Oh and here's the main.cpp for the testing project :
#include "MqlUtils.h"
#include "main.h"
extern __declspec(dllimport) int GetOrdersDetailsNoSymbol(int orderCount, char * MasterLicense, char * SlaveLicense, int orderTicket[], int op[],
double orderOpenPrice[], double orderStoploss[],
double orderTakeProfit[], double orderLots[], int orderDateTime[],
MqlStr* ordersymbol, MqlStr* ordercomments, int lotsCopyingMethod[], int returnedOrders[]);
void TestClient()
{
char* Master = "7C83C4C2";
char* Slave = "3B7C22A";
int returnedOrderCount[1] = {0};
double aStoredOrderOpenPrice[4];
int aStoredOrderType[4];
int aStoredOrderTicket[4];
double aStoredOrderStopLoss[4];
double aStoredOrdeTakeProfit[4];
double aStoredOrderLots[4];
int aStoredOrderDateTime[4];
int aStoredLotsMethods[4];
MqlStr* aStoredOrderComment[4];
MqlStr* aStoredOrderSymbol[4];
for (int i = 0; i < 4; i++)
{
aStoredOrderOpenPrice[i]= -1;
aStoredOrderType[i]= -1;
aStoredOrderTicket[i]= -1;
aStoredOrderStopLoss[i]= -1;
aStoredOrdeTakeProfit[i]= -1;
aStoredOrderLots[i]= -1;
aStoredOrderDateTime[i]= -1;
aStoredLotsMethods[i]= -1;
aStoredOrderComment[i]->len = 56;
aStoredOrderComment[i]->string = "11111111111111111111111111111111111111111111111111111111";
aStoredOrderSymbol[i]->len = 56;
aStoredOrderSymbol[i]->string = "11111111111111111111111111111111111111111111111111111111";
}
GetOrdersDetailsNoSymbol(1, Master, Slave, aStoredOrderTicket, aStoredOrderType,
aStoredOrderOpenPrice, aStoredOrderStopLoss,
aStoredOrdeTakeProfit, aStoredOrderLots, aStoredOrderDateTime,
*aStoredOrderSymbol, *aStoredOrderComment, aStoredLotsMethods, returnedOrderCount);
}
int main(int argc, char **argv)
{
TestClient();
return 0;
}
If anyone could help me solve this, I would be infinitely grateful.
Thanks for reading!
Your two declarations of GetOrdersDetailsNoSymbol do not match. In your header file you declare it with __stdcall and in main.cpp you don't. You should have only a single declaration. It can use #define and #ifdef to apply the dllimport or dllexport keywords as appropriate.
EDIT: Also, get rid of the extern "C" statements. And then use the DLLIMPORT #define to declare your function and only #define BUILDING_DLL in the build of your DLL.