Third Party Libraries
Using a third-party library with Qt is a simple process. Suppose you know of a cross-platform library that accepts audio samples of a cat's meows and translates them into English words. This library is named
CatWhisperer, and has several files that it provides as part of its library. Your project,
MyQtApp, stores these files in a folder named
To use the
CatWhisperer library in
qmake requires the location and names of the
CatWhisperer libraries. Optionally, you can also:
- Provide the location of the
CatWhisperersource code so that you don't have to type out the full path to each file when you include them in your own code.
- Choose the destination in which the
MyQtAppexecutable will be created.
The information above is provided in the
.pro file, so that
qmake can parse it and produce makefiles. Makefiles contain all the information needed by your compiler and linker to produce output, whether it is an executable, another library file, etc. The next sections explain the syntax with which
qmake expects you to provide this information.
To be able to write
you can provide the path to the
include directory, using the INCLUDEPATH variable:
INCLUDEPATH += 3rdparty/CatWhisperer/include
qmake know where to find the
CatWhisperer library files, use the LIBS variable:
LIBS += -L"3rdparty/CatWhisperer/lib" -lCatWhisperer
The first part of the expression lets the linker know in which directory it should look for the library files. The double quotes are only necessary when the path contains spaces, so we could have omitted them in this example.
The second part tells the linker which libraries to link against. We have two different library files for UNIX platforms and Windows, respectively:
CatWhisperer.lib. It is not necessary to specify the
.lib extension, nor the
lib prefix (on UNIX platforms).
qmake creates the executable in the same directory as the
.pro file. We can choose our own directory using the DESTDIR variable:
DESTDIR = bin
That's it! You can now use the
CatWhisperer library in your project. The final
.pro file looks like this:
TARGET = MyQtApp TEMPLATE = app INCLUDEPATH += 3rdparty/CatWhisperer/include SOURCES += src/main.cpp LIBS += -L"3rdparty/CatWhisperer/lib" -lCatWhisperer