apress foundations_of gtk plus development 2007 phần 4 ppsx

CHAPTER 5 ■ DIALOGS 157

After learning about the built-in dialogs, you learned about multiple types of built-in

dialogs provided by GTK+:

• Message dialog (GtkMessageDialog): Provide a general message, error message, warning,

or simple yes-no question to the user.

• About dialog (GtkAboutDialog): Show information about the application including ver￾sion, copyright, license, authors, and others.

• File chooser dialog (GtkFileChooserDialog): Allow the user to choose a file, choose mul￾tiple files, save a file, choose a directory, or create a directory.

• Color selection dialog (GtkColorSelectionDialog): Allow the user to choose a color along

with an optional opacity value.

• Font selection dialog (GtkFontSelectionDialog): Allow the user to choose a font and its

size and style properties.

The last section of this chapter showed you a widget called GtkAssistant, which was intro￾duced in GTK+ 2.10. It allows you to create dialogs with multiple stages. It is important to note

that assistants are not actually a type of GtkDialog widget but are directly derived from the

GtkWindow class. This means that you have to handle these by connecting signals in the main

loop instead of calling gtk_dialog_run().

You now have a firm understanding of many important aspects of GTK+. Before we con￾tinue on to more advanced widgets, the next chapter will give you a thorough understanding of

GLib. Chapter 6 will cover many GLib data types, idle functions, timeouts, process spawning,

threads, dynamic modules, file utilities, and timers, as well as other important topics.

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159

■ ■ ■

CHAPTER 6

Using GLib

Now that you have a reasonable grasp of GTK+ and a number of simple widgets, it is time to

move to another library. GTK+ depends on GLib, a general-purpose library that provides many

kinds of utility functions, data types, and wrapper functions. In fact, you have already used

some aspects of GLib in previous chapters.

GLib can be run independently of any other library, which means that some of the exam￾ples in this chapter do not require the GTK+, GDK, and Pango libraries. However, GTK+ does

depend on GLib.

Not all of the topics throughout this chapter will be used in later chapters, but all are useful

in many GTK+ applications in the real world. Many of the topics are used for very specific tasks.

For example, GModule can be used to create a plug-in system for your application or open a

binary’s symbol table.

The goal of Chapter 6 is not to be a comprehensive guide to everything in GLib. When

using a feature shown in this chapter, you should reference the GLib API documentation for

more information. However, this chapter will introduce you to a wide array of important fea￾tures so that you have a general understanding of what GLib provides.

In this chapter, you will learn the following:

• The basic data types, macros, and utility functions provided by GLib

• How to give textual feedback to the user about errors and warnings that occur within

your application

• Memory management schemes provided by GLib such as memory slices, g_malloc(),

and friends

• Various utility functions provided by GLib for timing, file manipulation, reading direc￾tory contents, and working with the file system

• How the main loop is implemented in GLib and how it implements timeout and idle

functions

• Data structures provided by GLib including strings, linked lists, binary trees, arrays, hash

tables, quarks, keyed data lists, and n-ary trees

• How to us GIOChannel to manipulate files and create pipes as well as how to spawn asyn￾chronous and synchronous processes

• How to dynamically load shared libraries with GModule

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160 CHAPTER 6 ■ USING GLIB

GLib Basics

GLib is a general-purpose utility library that is used to implement many useful nongraphical

features. While it is required by GTK+, it can also be used independently. Because of this, some

applications use GLib without GTK+ and other supporting libraries for the many capabilities it

provides.

One of the main benefits of using GLib is that it provides a cross-platform interface that

allows your code to be run on any of its supported operating systems with little to no rewriting

of code. You will see this illustrated in the examples throughout the rest of this chapter.

Basic Data Types

You have been using many data types in previous chapters that originate in GLib. These data

types provide a set of common data types that are portable to not only other platforms, but also

other programming languages wrapping GTK+.

Table 6-1 is a list of the basic data types provided by GLib. You can find all of the type def￾initions in the gtypes.h header file. More advanced data structures will be covered later, in the

“Data Types” section.

Table 6-1. GLib Data Types

Type Description

gboolean Since C does not provide a Boolean data type, GLib provides gboolean, which

is set to either TRUE or FALSE.

gchar (guchar) Signed and unsigned data types corresponding to the standard C character type.

gconstpointer A pointer to constant data that is untyped. The data that this type points to

should not be changed. Therefore, it is typically used in function prototypes

to indicate that the function will not alter the data to which it points.

gdouble A data type corresponding to the standard C double type. Possible values are

within the range from -G_MAXDOUBLE to G_MAXDOUBLE. G_MINDOUBLE refers to the

minimum positive value that gdouble can hold.

gfloat A data type corresponding to the standard C float type. Possible values are

within the range from -G_MAXFLOAT to G_MAXFLOAT. G_MINFLOAT refers to the

minimum positive value that gfloat can hold.

gint (guint) Signed and unsigned data types corresponding to the standard C int

type. Signed gint values must be within the range from G_MININT to

G_MAXINT. The maximum guint value is given by G_MAXUINT.

gint8 (guint8) Signed and unsigned integers that are designed to be 8 bits on all

platforms. Signed values are within the range from -128 to 127 (G_MININT8

to G_MAXINT8) and unsigned values from 0 to 255 (G_MAXUINT8).

gint16 (guint16) Signed and unsigned integers that are designed to be 16 bits on all

platforms. Signed values are within the range from -32,768 to 32,767

(G_MININT16 to G_MAXINT16) and unsigned values from 0 to 65,535

(G_MAXUINT16).

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