how to add zlib to an existing qt installation

How can I add zlib to an existing installation of Qt. I m pretty new in this so please give me detailed description! Thanks for your help in advance!

zlib is contained in the core Qt libraries. If you want to use the zlib functions in a Qt program, you only have to include zlib.h which is in src/3rdparty/zlib. See e.g. the implementation of QByteArray in src/corelib/tools.

If you want to use quazip, just add the library to your project. It is based on the Qt libraries. Take care to build the correct qyazip library that corresponds to your Qt installation.

You get the correct include path by adding the following line to your project file:

INCLUDEPATH += $$[QT_INSTALL_PREFIX]/src/3rdparty/zlib

For Qt5, see Thorbjørn's comment: it is sufficient to use #include <QtZlib/zlib.h>.

The current answer is only valid for Qt4. Since Qt5 the zlib header file is stored in a different directory. Using the qmake property QT_INSTALL_HEADERS you can add to your .pro file:

INCLUDEPATH += $$[QT_INSTALL_HEADERS]/QtZlib

This works e.g. to build quazip, if you add it to quazip.pro

The property $$[QT_INSTALL_HEADERS] points to QTDIR/qtbase/include/ within which lies QtZlib/zlib.h.

Without changing the includepath you have to change every include-statement to #include <QtZlib/zlib.h> as commented by Thorbjørn.