Undefined refence to '_imp__FunctionName'

[MNag]

Hello, i am trying to build a simple Qt project which is calling dll (dll built from Embarcadero C++ Builder) function but i have a undefined reference to that function.
Checked for function declaration , definition everything looks good.
i am using QT 5.15.2 Windows, MinGW 32 bit.

This is how my .pro looks

QT -= gui

CONFIG += c++11 console
CONFIG -= app_bundle

You can make your code fail to compile if it uses deprecated APIs.

In order to do so, uncomment the following line.

#DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0x060000 # disables all the APIs deprecated before Qt 6.0.0

SOURCES +=
main.cpp

Default rules for deployment.

qnx: target.path = /tmp/$${TARGET}/bin
else: unix:!android: target.path = /opt/$${TARGET}/bin
!isEmpty(target.path): INSTALLS += target

#LIBS += "..\MyDll\DLLProj.dll"

HEADERS +=
myDll.h

DISTFILES +=
DLLProj1.a# \

DllProj1.def

#win32: LIBS += -L$$PWD/./ -lDLLProj

#INCLUDEPATH += $$PWD/.
#DEPENDPATH += $$PWD/.

[SGaist]

Hi,

Where the symbols of that method properly exported ?
Is that compiler compatible with the one you are using currently ? You can't mix and match libraries from different compilers. For example MinGW and VS cannot be mixed.
Is the library of the same architecture as your main application ?

[MNag]

@SGaist

Hi, Thanks for reply!!

I am new to C++ builder not sure about the compiler compatible need to check on that.

this is how i am exporting the function in dll source code using Emberacadero C++ builder.

extern "C" __declspec(dllexport) void myfun ( int * a);

[MNag]

@SGaist

BCC32C this is the compiler name which is used in Embarcadero C++ builder

[SGaist]

You seem to be doing some pretty convoluted things here.

Your method seems to be a pure C method that you try to wrap in a C++ library so you should rather build a C dll that does not have the same constraints as a C++ dll. As for your use of the __declspec instruction, it's wrong. You have to export the symbol on build and then import the symbol when linking to the library.

For building C++ shared library, the dedicated chapter in Qt's documentation explains it pretty well.

[MNag]

@SGaist

i tried as below aswell but still have same issue

#ifdef IN_DLL
#define EXPORT_IMPORT __export
#else
#define EXPORT_IMPORT Q_DECL_IMPORT //__import
#endif

#ifdef BORLANDC
extern "C" void __stdcall EXPORT_IMPORT myfun( int * a);
#else
extern "C" void __stdcall EXPORT_IMPORT myfun( int * a);
#endif

Earlier i was using:

i was exporting on C++ builder side and importing in QT using following

QT:
extern "C" __declspec(dllimport) void myfun( int * a);

C++ Builder:
extern "C" __declspec(dllexport) void myfun( int * a);

[SGaist]

Again: why are you trying to make a C++ library if you have only C functions ? It really complicate things for nothing.

[MNag]

@SGaist

Actually i want to migrate old dll project (big project) to C++ Builder in that they are using above mentioned method soi thought it will be convenient to do the same.

[SGaist]

That starts to make things a bit clearer.

On a side note, you used the Qt macros wrongly.

So your original dll is a C dll that you would like to port to C++ and you are using the technique you saw from the use of the library by the Borland compiler ?

[MNag]

@SGaist

Yes, that's Correct.

What's wrong with Qt macros?

[SGaist]

You did not use Q_DECL_EXPORT.

[MNag]

@SGaist said in Undefined refence to '_imp__FunctionName':

Q_DECL_EXPORT.

Thought of using the C++ builder macro for exporting since i am exporting in C++ builder and importing in Qt so i used Qt macro for importing.