I created by the first time a dll to use with C++ (and then C#, I have plans to share this dll between a C++ and C# applications) using QT creator but when I try to use it I get SEGFAULT error.
Here's my files:
mydll.h
#ifndef MYDLL_H
#define MYDLL_H
#include "mydll_global.h"
class MYDLLSHARED_EXPORT MyDll
{
public:
MyDll();
int getAnswer();
};
MYDLLSHARED_EXPORT int getNumber();
#endif // MYDLL_H
mydll_global.h
#ifndef MYDLL_GLOBAL_H
#define MYDLL_GLOBAL_H
#include <QtCore/qglobal.h>
#if defined(MYDLL_LIBRARY)
# define MYDLLSHARED_EXPORT Q_DECL_EXPORT
#else
# define MYDLLSHARED_EXPORT Q_DECL_IMPORT
#endif
#endif // MYDLL_GLOBAL_H
mydll.cpp
#include "mydll.h"
MyDll::MyDll()
{
}
int MyDll::getAnswer()
{
return 42;
}
int getNumber()
{
return 10;
}
So I build it and created mydll.dll: then I went to other C++ project wheere I want to use this dll and put in the .pro file:
LIBS += "C:\path\to\mydll.h"
and in the main.cpp
#include "mydll.h"
and when I use function from dll like this:
qDebug() << getNumber();
I get a SEGFAULT error.
I thought that the header to provide the compiler type information and the dll to compiler to provide the function body was all I needed but as I'm getting a SEGFAULT I'm acessing NULL or someone else memory or so (I can't see the value on debug).
What am I missing?
First off, to link the DLL you need the link .lib file for that DLL. That file has all the binary manifest for linking.
Second, project file LIBS clause specify the list of .lib files to link with. Some of them may represent dynamic libraries (.dll).
See the example: Linking to Shared Library in Qt
Even better article covering both creation of DLL with Qt and using DLL in your Qt project: https://wiki.qt.io/How_to_create_a_library_with_Qt_and_use_it_in_an_application
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