7.1.2. Installing Libraries

7.1.2. Installing Libraries
	7.1. Building and Reusing Libraries

[ fromfile: reusinglibs.xml id: installingsoftware ]

When a library is built, it is placed in the directory specified by the qmake variable DESTDIR.
For example, the project file for our dataobjects library contains the following relevant lines:

TEMPLATE = lib      # Build this as a library, not as an application
DESTDIR=$$(CPPLIBS) # Place the compiled shared object code here

Build libraries in your CPPLIBS directory.
On a *nix system, add the line
```
export LD_LIBRARY_PATH=$CPPLIBS
```
to your .bashrc file, below the line in which you define CPPLIBS.
The superuser of your *nix system can install the library in /usr/local, a systemwide location accessible to all other users.

QTDIR

	QTDIR
The environment variable `QTDIR` is not required by Qt, but we sometimes use it in different parts of the book to refer to the base directory of an unzipped Qt tarball. It provides a convenient way to refer to the location of the examples, tutorials, binaries, and libraries of Qt. However, on systems like Ubuntu or Debian, where Qt is split into multiple folders and installed to different locations, `QTDIR` should not be, and is not defined (if you are using the distro's version of Qt). In that case, you can interpret our usage of QTDIR to mean "the parent directory of the Qt binaries" or "the parent directory of the Qt examples" (which may be two different directories in that case).

The environment variable QTDIR is not required by Qt, but we sometimes use it in different parts of the book to refer to the base directory of an unzipped Qt tarball. It provides a convenient way to refer to the location of the examples, tutorials, binaries, and libraries of Qt. However, on systems like Ubuntu or Debian, where Qt is split into multiple folders and installed to different locations, QTDIR should not be, and is not defined (if you are using the distro's version of Qt). In that case, you can interpret our usage of QTDIR to mean "the parent directory of the Qt binaries" or "the parent directory of the Qt examples" (which may be two different directories in that case).

	QLibrary
	The `QLibrary` class has methods to help you load and unload dynamic libraries at runtime in a platform-independent way.


7.1.1. Organizing Libraries: Dependency Management		7.2. Exercise: Installing Libraries