Problem linking external libraries to .pro file

[ChrisW67]

I really am struggling with why the simple task of linking to an external library causes so many people grief.

Set up the library

Starting with the source tar ball, build and install libvlc-qt:

tar xzf libvlc-qt_0.4.0_src.tar.gz
cd libvlc-qt-0.4.0/
mkdir build
cd build
cmake .. -DCMAKE_INSTALL_PREFIX=/usr
make
make install

tar xzf libvlc-qt_0.4.0_src.tar.gz
cd libvlc-qt-0.4.0/
mkdir build
cd build
cmake .. -DCMAKE_INSTALL_PREFIX=/usr
make
make install

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Compile your program

At this point your compiler will find the include files and link libraries on its own. The library will be found at runtime.

However, if you use a different install prefix, for example /usr/local, then you need these in your pro file:

INCLUDEPATH += /usr/local/include
LIBS += -L/usr/local/lib

INCLUDEPATH += /usr/local/include
LIBS += -L/usr/local/lib

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to tell the compiler and linker where to look.

In all cases you need to tell Qt to link the vlc-qt library into your program:

LIBS+= -lvlc-qt

LIBS+= -lvlc-qt

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At this point the program is compiling and linking.


Running the Program

If you used the standard install prefix then your program will just run without further effort.

If you have not used a "standard" install prefix then the runtime library will not be found when you try to run it. You can use LD_LIBRARY_PATH variable to locally change the run time library search path.

export LD_LIBRARY_PATH=/some/odd/install/prefix/lib
./my_program

export LD_LIBRARY_PATH=/some/odd/install/prefix/lib
./my_program

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