How to add a lib to a qt project

[WilliamSpiderWeb]

I hope I understood it the right way.
My main() is looking like this now:

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    a.addLibraryPath("C:/Qt/2010.05/qt/plugins/sqldrivers");
    MainWindow w;
    w.show();
    return a.exec();
}

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    a.addLibraryPath("C:/Qt/2010.05/qt/plugins/sqldrivers");
    MainWindow w;
    w.show();
    return a.exec();
}

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But the available drivers are still the same.
The Question is, how should the software know which dll I need. It just knows where the dlls are located.

[stampede]

No, I mean the "parent" directory for plugins:

QApplication::addLibraryPath("C:/Qt/2010.05/qt/plugins"); // without "sqldrivers"

QApplication::addLibraryPath("C:/Qt/2010.05/qt/plugins"); // without "sqldrivers"

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[WilliamSpiderWeb]

sorry, I tried first without "sqldrivers" and after it with "sqldrivers".
But I qoute the wrong codeline to my reply

[stampede]

So it looks like you'll need to build it indeed - its quite easy, just follow the link ChrisW67 gave you in previous post (there is QPSQL section).

[WilliamSpiderWeb]

I tried to build the psql plugin before,
but even there I need some support.

The doc says I have to use these commands

cd %QTDIR%\src\plugins\sqldrivers\psql
 qmake "INCLUDEPATH+=C:\psql\include" "LIBS+=C:\psql\lib\ms\libpq.lib" psql.pro
 nmake

cd %QTDIR%\src\plugins\sqldrivers\psql
 qmake "INCLUDEPATH+=C:\psql\include" "LIBS+=C:\psql\lib\ms\libpq.lib" psql.pro
 nmake

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when I type the second command (yes I used the right path for psql) I get no error but the psql.pro file is still empty.

when I type the nmake my windows tells me it cannot find nmake. And I can't find nmake in the qt directory either.

At this point I have to say, thanks for your effort and patience.

[wysota]

I think the "problem" is a missing PostgreSQL dll, not the Qt driver. The driver also needs the dll.

[ChrisW67]

Stampede spake saying:

The thing is that this plugin is probably already built ( qsqlpsql.dll exisits in his Qt installation ).

and WilliamSpiderWeb wrote earlier:

I got the lib from a friend of mine. He used it to communicate to a postgres db with a Visual C++ project (without MFC).

and gave us error messages from the GNU ld, i.e. the MingW compiler suite.

It took this to mean that his friend built the plugin with MSVC, and that WilliamSpiderWeb is using MingW. This plugin will not load into a MingW-built program for a variety of reasons. That's why I suggested building the plugin. Perhaps someone else can tell us if PostgreSQL would also have to built with MingW or if the downloadable binaries are sufficient?


To address one of the plugin build issues...

nmake is the make utility from the MSVC compiler suite. You are using the MingW compiler bundled in the Qt SDK. The equivalent command would be:

mingw32-make

mingw32-make

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[stampede]

ChrisW67, you are probably right, I just assumed that the qt plugin was built during Qt installation.
I've just downloaded PostgreSQL from here : link (Binaries from installer version 8.4.7-1 for Windows), and it took me 30 sec. to build the plugin (g++ 4.5.2):

cd C:\Qt\src\plugins\sqldrivers\psql
qmake "INCLUDEPATH+=C:\pgsql\include" "LIBS+=C:\pgsql\lib\libpq.lib" psql.pro
make

cd C:\Qt\src\plugins\sqldrivers\psql
qmake "INCLUDEPATH+=C:\pgsql\include" "LIBS+=C:\pgsql\lib\libpq.lib" psql.pro
make

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Just make sure that path in INCLUDEPATH and LIBS is correct.

[WilliamSpiderWeb]

I'm not sure what I am doing wrong.
I started cmd, then moved to the directory "..\src\plugin\sqldrivers\psql".
The psql-folder was just created by me.
Now I typed the following command.

c:\qt\2010.05\qt\qmake\qmake.exe "INCLUDEPATH+=C:\psql9\include" "LIBS+=C:\psql9\lib\libpg.lib" psql.pro

c:\qt\2010.05\qt\qmake\qmake.exe "INCLUDEPATH+=C:\psql9\include" "LIBS+=C:\psql9\lib\libpg.lib" psql.pro

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The error message I get is

Cannot find file: psql.pro

When I create an empty textfile or copy an existing *.pro file to the directory "...sqldrivers\psql" I get the following error message

QMAKESPEC has not been set, so configuration cannot be deduced.
Error processing project file: psql.pro

[wysota]

Hmm... sorry for asking but what are you trying to do?

[WilliamSpiderWeb]

Am I on the completly wrong way?

I want my qt App communicate with a postgresql database.
Chris and stampede told me I have to build a psql plugin for qt.

That's what I'm actually trying to do.

cd C:\Qt\src\plugins\sqldrivers\psql
qmake "INCLUDEPATH+=C:\pgsql\include" "LIBS+=C:\pgsql\lib\libpq.lib" psql.pro
make

cd C:\Qt\src\plugins\sqldrivers\psql
qmake "INCLUDEPATH+=C:\pgsql\include" "LIBS+=C:\pgsql\lib\libpq.lib" psql.pro
make

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If I just type qmake, my pc cannot find the command. That's why I typed the whole path of qmake.exe.
And postgres is installed in C:\psql9 on my computer.
And as you can read in my last reply, it doesn't work on my computer.

[wysota]

I want my qt App communicate with a postgresql database.
Chris and stampede told me I have to build a psql plugin for qt.

And you intend to do it by compiling a project from a directory that doesn't contain any source (nor other project) files? You expect some magic to happen that your compiler knows how to build that plugin from an empty directory?

The psql-folder was just created by me.

You shouldn't be creating any directories. Qt sources should contain a psql directory inside src/plugins/imageformats and there should be a bunch of files there including a README file containing requirements and instructions for building the plugin.