Qt DLL (MinGW) for VB (VBA)

[MChe]

Hello!

I want to create Qt DLL for VB (VBA).

I find out how I can do it via c++ (https://stackoverflow.com/questions/2720246/how-to-create-dll-using-gcc-compiler-mingw-for-visual-basic). I use 'gcc fooBar.cpp -shared -Wl,--kill-at -o fooBar.dll'. It's work in VBA (Excel).

But I can't do it with Qt :( Have anybody example source of Qt DLL for VBA? How can I use something like 'gcc fooBar.cpp -shared -Wl,--kill-at -o fooBar.dll' in Qt Creator?

[hskoglund]

Hi, it's actually easier with Qt, you don't have to specify any command line switches to gcc. You start by creating a Library (C++ library), Standard Library, then select the Qt modules you need (I tried just with QtCore).
I just tested with a global function in my untitled.cpp (also I used extern "C" to simplify):

extern "C" __declspec(dllexport) int __stdcall square_int(int x)
{
    return x * x;
}

Build it in Release mode (not Debug). To make the untitled.dll loadable by Excel, all the Qt and MinGW .dlls needed, like libwinpthread-1.dll, libgcc_s_dw2-1.dll, Qt5Core.dll etc. needs to be visible in the PATH environment variable.

In Excel, test the following VBA code in Book1 - Sheet1:

Private Declare Function square_int Lib _
    "C:\Projects\build-untitled-Desktop_Qt_5_6_2_MinGW_32bit-Release\release\untitled.dll" Alias "square_int@4" _
(ByVal x As Long) As Long

Sub test()
Debug.Print square_int(5)
End Sub

In the Immediate window in Excel's VBA window ' 25' should appear!

P.S. (I can't figure out right now how to call the VBA code from inside a cell in the spreadsheet, =square_int(5) does not work, but maybe something similar :-)

[MChe]

@hskoglund Thx, It's work!

But I want to use Qt features in VBA (QWidgets, signals and slots, etc.).

DLLTestOne.pro

QT       += widgets network

TARGET = DLLTestOne
TEMPLATE = lib

DEFINES += DLLTESTONE_LIBRARY

SOURCES += \
        dlltestone.cpp

HEADERS += \
        dlltestone.h \
        dlltestone_global.h 

unix {
    target.path = /usr/lib
    INSTALLS += target
}

dlltestone.h

#ifndef DLLTESTONE_H
#define DLLTESTONE_H

#include "dlltestone_global.h"

class DLLTESTONESHARED_EXPORT DLLTestOne
{

public:
    DLLTestOne();
};

#endif // DLLTESTONE_H

dlltestone_global.h

#ifndef DLLTESTONE_GLOBAL_H
#define DLLTESTONE_GLOBAL_H

#include <QtCore/qglobal.h>
#include <QApplication>

#if defined(DLLTESTONE_LIBRARY)
#  define DLLTESTONESHARED_EXPORT Q_DECL_EXPORT
#else
#  define DLLTESTONESHARED_EXPORT Q_DECL_IMPORT
#endif

#endif // DLLTESTONE_GLOBAL_H

dlltestone.cpp

#include "dlltestone.h"


DLLTestOne::DLLTestOne()
{
}

extern "C" __declspec(dllexport) int __stdcall square_int(int x)
{
    char  arg0[] = "programName1";
    char  arg1[] = "arg";
    char  arg2[] = "another arg";
    char* argv[] = { &arg0[0], &arg1[0], &arg2[0], NULL };
    int   argc   = (int)(sizeof(argv) / sizeof(argv[0])) - 1;

    QApplication a(argc, &argv[0]);

    return a.exec();
}

If I run 'square_int' in VBA, I have error: The application failed to start because it could not find or load the Qt platform plugin "windows" in "".

When I run simple Qt exe, It's run ok. I try to create folder "platform" with "qwindows.dll" everywhere, I haven't result :(

VBA:

Private Declare Function square_int Lib _
    "P:\Mydocuments\QtProject\DLLTestOne\build-DLLTestOne-Desktop_Qt_5_9_0_MinGW_32bit-Release\release\DLLTestOne.dll" Alias "square_int@4" _
(ByVal x As Long) As Long

Sub test()
Debug.Print square_int(5)
End Sub

Setting QT_QPA_PLATFORM_PLUGIN_PATH doesn't help.

[MChe]

Sorry, I have its problem for all Qt apps on PC. I will try to fix it.