Qt/C++ - Lesson 025. Creating Project Files

sources, headers, qt, config, libs, qt5, qmake

Project files contain all the information required by qmake to build your application, library, or plugin. Generally, you use a series of declarations to specify the resources in the project, but support for simple programming constructs enables you to describe different build processes for different platforms and environments.

Project File Elements

The project file format used by qmake can be used to support both simple and fairly complex build systems. Simple project files use a straightforward declarative style, defining standard variables to indicate the source and header files that are used in the project. Complex projects may use control flow structures to fine-tune the build process.

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 lists 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 snippet illustrates how lists of values are assigned to variables:

HEADERS = mainwindow.h paintwidget.h

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

SOURCES = main.cpp mainwindow.cpp \
          paintwidget.cpp
CONFIG += console

Note: The first assignment only includes values that are specified on the same line as the

HEADERS

SOURCES

The CONFIG variable is another special variable that qmake uses when generating a Makefile.

Variables list

The following table lists some frequently used variables and describes their contents.

• CONFIG - General project configuration options.
• DESTDIR - The directory in which the executable or binary file will be placed.
• FORMS - A list of UI files to be processed by the user interface compiler (uic).
• HEADERS - A list of filenames of header (.h) files used when building the project.
• QT - A list of Qt modules used in the project.
• RESOURCES - A list of resource (.qrc) files to be included in the final project.
• SOURCES - A list of source code files to be used when building the project.
• TEMPLATE - The template to use for the project. This determines whether the output of the build process will be an application, a library, or a plugin.

The contents of variables can be assigned to other variables by the substitution of two signs $ before the name of the other variables.

Whitespace

Usually, whitespace separates values in variable assignments. To specify values that contain spaces, you must enclose the values in double quotes:

DEST = "Program Files"

The quoted text is treated as a single item in the list of values held by the variable. A similar approach is used to deal with paths that contain spaces, particularly when defining the INCLUDEPATH and LIBS variables for the Windows platform:

win32:INCLUDEPATH += "C:/mylibs/extra headers"
unix:INCLUDEPATH += "/home/user/extra headers"

Comments

You can add comments to project files. Comments begin with the

#

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

Built-in Functions and Control Flow

qmake provides a number of built-in functions to enable the contents of variables to be processed. The most commonly used function in simple project files is the include() function which takes a filename as an argument. The contents of the given file are included in the project file at the place where the

include

include

include(other.pro)

Support for conditional structures is made available via scopes that behave like

if

win32 {
    SOURCES += paintwidget_win.cpp
}

The assignments inside the braces are only made if the condition is true. In this case, the

**win32**

More complex operations on variables that would usually require loops are provided by built-in functions such as find() , unique() , and count() . These functions, and many others are provided to manipulate strings and paths, support user input, and call external tools.

Project Templates

The TEMPLATE variable is used to define the type of project that will be built. If this is not declared in the project file, qmake assumes that an application should be built, and will generate an appropriate Makefile (or equivalent file) for the purpose.

The following table summarizes the types of projects available and describes the files that qmake will generate for each of them:

• app (default) - Makefile to build an application.
• lib - Makefile to build a library.
• aux - Makefile to build nothing. Use this if no compiler needs to be invoked to create the target, for instance because your project is written in an interpreted language. Note: This template type is only available for Makefile-based generators. In particular, it will not work with the vcxproj and Xcode generators.
• subdirs - Makefile containing rules for the subdirectories specified using the SUBDIRS variable. Each subdirectory must contain its own project file.
• vcapp - Visual Studio Project file to build an application.
• vclib - Visual Studio Project file to build a library.
• vcsubdirs - Visual Studio Solution file to build projects in sub-directories.

When the

subdirs

make

SUBDIRS

General Configuration

The CONFIG variable specifies the options and features that the project should be configured with.

The project can be built in release mode or debug mode, or both. If debug and release are both specified, the last one takes effect. If you specify the

debug_and_release

make all

Adding the build_all option to the CONFIG variable makes this rule the default when building the project.

Note: Each of the options specified in the

CONFIG

opengl

CONFIG(opengl) {
    message(Building with OpenGL support.)
} else {
    message(OpenGL support is not available.)
}

This enables different configurations to be defined for

release

debug

Note: Some of these options only take effect when used on the relevant platform.

• qt - The project is a Qt application and should link against the Qt library. You can use the

  QT

  variable to control any additional Qt modules that are required by your application. This value is added by default, but you can remove it to use qmake for a non-Qt project.
• x11 - The project is an X11 application or library. This value is not needed if the target uses Qt.

Template applications and libraries provide you with more specialized settings of the assembly process. For example, if your application uses the Qt library and you want to build it in

debug

CONFIG += qt debug

Note: You must use "+=", not "=", or qmake will not be able to use Qt's configuration to determine the settings needed for your project.

Declaring Qt Libraries

If the CONFIG variable contains the

qt

QT += network xml

Note:

QT

core

gui

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

If you want to build a project without the

gui

QT

core

gui

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

Configuration Features

qmake can be set up with extra configuration features that are specified in feature (.prf) files. These extra features often provide support for custom tools that are used during the build process. To add a feature to the build process, append the feature name (the stem of the feature filename) to the

CONFIG

For example, qmake can configure the build process to take advantage of external libraries that are supported by pkg-config, such as the D-Bus and ogg libraries, with the following lines:

CONFIG += link_pkgconfig
PKGCONFIG += ogg dbus-1

Declaring Other Libraries

If you are using other libraries in your project in addition to those supplied with Qt, you need to specify them in your project file.

The paths that qmake searches for libraries and the specific libraries to link against can be added to the list of values in the LIBS variable. You can specify the paths to the libraries or use the Unix-style notation for specifying libraries and paths.

LIBS += -L/usr/local/lib -lmath

The paths containing header files can also be specified in a similar way using the INCLUDEPATH variable.

INCLUDEPATH = c:/msdev/include d:/stl/include