[Qt-interest] Making a Qt program into a dynamic library

[Konrad Rosenbaum]

Hi,

I'll answer anyway, since more is amiss here...

The extern "C" should not matter since your loader does not access the 
symbols.

On Wednesday 16 December 2009 11:50:43 Guido Seifert wrote:
> This is extremely strange. Here the very simple plugin I just tried:
>
> MyTest.cpp:
>
> #include <QString>

extern "C" is missing.

> void start()
> {
>  QString str;
> }
>
> MyTest.pro:
>
> SOURCES += MyTest.cpp
>
> CONFIG += qtcore

I'm not sure what the above does - it should not be necessary.

> CONFIG -= thread

Hmm. This should neither be necessary, nor wise. Qt4 has threads compiled in 
mandatorily (except one one or two embedded systems).

> CONFIG += shared
>
> TEMPLATE = lib
> MOC_DIR = ./.moc
> OBJECTS_DIR = ./.obj

ok, but the TARGET directive is missing

> Above results in libMyTest.so.1.0.0
> The test program, which loads the lib:

#include is missing

> int main(int argc, char *argv[])
> {
>   void* handle = dlopen("./libMyTest.so.1.0.0", RTLD_LAZY);
>   return 0;
> }

looks ok, but how is it compiled?

gcc -o m mymain.c -ldl
works fine for me

> Result: segfault
> Same happens when I comment out the QString.

No segfault here.

There was another conflict somewhere. It probably went away when you 
recompiled everything. I guess you compiles against one version of Qt and 
executed with another.

> As I said, having CONFIG += qtcore (or += qt) in .pro file is enough to
> ensure the crash. Clearly no global variables on my side.

As said: this should not be necessary, qmake always assumes that QtCore and 
QtGui are in.

> What Qt version do you use?

Debians 4:4.5.3-4 and I just retried it with a 4.6.0 that I compiled myself.


	Konrad
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