Is there any way to load a library dynamically?
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Hi, I use Qt 4.7 on a Mac. I created several custom widgets. These widgets are compiled into a .dylib file installed in designer's plugin directory. When I open the designer in the Qt Creator, the .dylib is loaded. So I can use my widgets in my .ui file without any problem. Now I want to create different versions of the widgets/.dylib for different projects. And I want to load the right version of the .dylib for a specific project. Is there any way to achieve this?
Thanks!
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If you mean loading DLLs at runtime, you need to use QLibrary.
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[quote author="sierdzio" date="1376111760"]If you mean loading DLLs at runtime, you need to use QLibrary.[/quote]
AFAIK, this only works with "plain C" functions, but not with C++ objects. I never managed to load C++ objects dynamically (at runtime) from a DLL. It requires linking against the DLL via import library (.LIB file), I think.
One workaround is to export some wrapper functions from the DLL:
@#include "MyClass.h"extern "C"
{
__declspec(dllexport) MyClass* __cdecl newObject(void)
{
return new MyClass();
}
__declspec(dllexport) int __cdecl useObject(MyClass *o)
{
return o->doSomethingInteresting();
}
__declspec(dllexport) void __cdecl delObject(MyClass *o)
{
delete o;
}
}@Then use like this in the EXE file:
@class MyClass;extern "C"
{
typedef MyClass* (*NewObjetFunc)(void);
typedef int (UseObjetFunc)(MyClass);
typedef void (DelObjetFunc)(MyClass);
}NewObjectFunc newObjectPtr = NULL;
UseObjectFunc useObjectPtr = NULL;
DelObjectFunc delObjectPtr = NULL;QLibrary myLib("MyLibrary.dll")
if(myLib.load())
{
newObjectPtr = (NewObjectFunc) myLib.resolve("newObject");
useObjectPtr = (UseObjectFunc) myLib.resolve("useObject");
delObjectPtr = (DelObjectFunc) myLib.resolve("delObject");
}if(newObjectPtr && useObjectPtr && delObjectPtr)
{
MyClass *obj = newObjectPtr();int result = useObjectPtr(obj); //Actually use object here! delObjectPtr(obj); obj = NULL;}@
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QLibrary is - as MuldeR said - for C functions resolving.
You can use QPlugInLoader for loading C++ functions, but only when they are using "Qt plugin mechanismns":http://qt-project.org/doc/qt-5.0/qtcore/plugins-howto.html. Or link to them dynamically.Please note that for C++ symbol resolving the various things (e.g., compiler version, build mode, etc.) need to match in order to load a plugin successfully.
