qmake Project Files

Variables

In a project file, variables are used to hold lists of strings. In the simplest projects, these variables inform qmake about the configuration options to use, or supply filenames and paths to use in the build process.

qmake looks for certain variables in each project file, and it uses the contents of these to determine what it should write to a Makefile. For example, the list of values in the HEADERS and SOURCES variables are used to tell qmake about header and source files in the same directory as the project file.

Variables can also be used internally to store temporary lists of values, and existing lists of values can be overwritten or extended with new values.

The following lines show how lists of values are assigned to variables:

    HEADERS = mainwindow.h paintwidget.h

Note that the first assignment only includes values that are specified on the same line as the SOURCES variable. The second assignment splits the items across lines by using the \ character.

The list of values in a variable is extended in the following way:

    SOURCES = main.cpp mainwindow.cpp \
              paintwidget.h
    CONFIG += qt

The CONFIG variable is another special variable that qmake uses when generating a Makefile. It is discussed in the section on configuration later in this chapter. In the above line, QT is added to the list of existing values contained in CONFIG.

The following table lists the variables that qmake recognizes, and describes what they should contain.

The contents of a variable can be read by prepending the variable name with $$. This can be used to assign the contents of one variable to another:

    TEMP_SOURCES = $$SOURCES

The $$ operator is used extensively with built-in functions that operate on strings and lists of values. These are described in the chapter on qmake Advanced Usage.

Normally, variables are used to contain whitespace-separated lists of values. However, it is sometimes necessary to specify values containing spaces. These must be quoted in the following way:

    DEST = "Program Files"

The quoted text is treated as a single item in the list of values held by the variable.

    # Comments usually start at the beginning of a line, but they
    # can also follow other content on the same line.

    include(other.pro)

    win32 {
        SOURCES += paintwidget_win.cpp
    }

    EXTRAS = handlers tests docs
    for(dir, EXTRAS) {
        exists($$dir) {
            SUBDIRS += $$dir
        }
    }

    CONFIG += qt thread debug

    CONFIG += qt
    QT += network xml

    QT = network xml # This will omit the core and GUI modules.

    QT -= gui # Only the core module is used.

        CONFIG += link_pkgconfig
        PKGCONFIG += ogg dbus-1