OOP Using GObject (1) – A Fundamental Type

These days, I tried to write C code with OO support. I found GObject is such a well-designed library to simplify my implementation. However, the official documents is not so clear sometimes. It do not provide sufficient information about all its stuff. I had to write my own demo applications to test the usage of some function. Moreover, the source code were also checked for reference.

There are 3 types in GObject type system: Fundamental, static and dynamic. Fundamental types are top-most types. The do not have parent types. They are seldom used, since all fundamental types are pre-defined rather than user-defined.

In this article, I will try to define a fundamental type using in GObject.Here’s the code on how to register a basic fundamental type in GObject, and how it can be used.

NOTE: PLEASE READ ALL COMMENT CAREFULLY.

#include <stdio.h>
#include <glib-object.h>

int main() {
    /* Initialize type system */
    g_type_init();

    /* This is not important */
    GTypeInfo my_type_info = { 0, NULL, NULL, NULL, NULL, NULL, 0, 0, NULL, NULL };
    /* This is not important */
    GTypeFundamentalInfo my_type_fundamental_info = { 0 };
    /* Register a fundamental type */
    GType my_type_id = g_type_register_fundamental(g_type_fundamental_next(),
        "MyFundamentalType", &my_type_info, &my_type_fundamental_info, 0);

    /* Print type names */
    printf("Type name of int: %s\n", g_type_name(G_TYPE_INT));
    printf("Type name of float: %s\n", g_type_name(G_TYPE_FLOAT));
    printf("Type name of object: %s\n", g_type_name(G_TYPE_OBJECT));
    printf("Type name of my fundamental type: %s\n", g_type_name(my_type_id));
    /* Print type id and name of MyFundamentalType */
    printf("Type id: %d\n", g_type_from_name("MyFundamentalType"));
    printf("Type name: %s\n", g_type_name(g_type_from_name("MyFundamentalType")));
    /* Print attributes of MyFundamentalType */
    printf("Is fundamental? %s\n", G_TYPE_IS_FUNDAMENTAL(my_type_id) ? "yes" : "no");
    printf("Is derived? %s\n", G_TYPE_IS_DERIVED(my_type_id) ? "yes" : "no");
    printf("Is interface? %s\n", G_TYPE_IS_INTERFACE(my_type_id) ? "yes" : "no");
    printf("Is classed? %s\n", G_TYPE_IS_CLASSED(my_type_id) ? "yes" : "no");
    printf("Is instantiatable? %s\n", G_TYPE_IS_INSTANTIATABLE(my_type_id) ? "yes" : "no");
    printf("Is derivable? %s\n", G_TYPE_IS_DERIVABLE(my_type_id) ? "yes" : "no");
    printf("Is deep derivable? %s\n", G_TYPE_IS_DEEP_DERIVABLE(my_type_id) ? "yes" : "no");
    printf("Is abstract? %s\n", G_TYPE_IS_ABSTRACT(my_type_id) ? "yes" : "no");
    printf("Is value abstract? %s\n", G_TYPE_IS_VALUE_ABSTRACT(my_type_id) ? "yes" : "no");
    printf("Is value type: %s\n", G_TYPE_IS_VALUE_TYPE(my_type_id) ? "yes" : "no");
    printf("Has value table: %s\n", G_TYPE_HAS_VALUE_TABLE(my_type_id) ? "yes" : "no");

    return 0;
}

#include <stdio.h>

#include <glib-object.h>

int main() {

/* Initialize type system */

g_type_init();

/* This is not important */

GTypeInfo my_type_info = { 0, NULL, NULL, NULL, NULL, NULL, 0, 0, NULL, NULL };

/* This is not important */

GTypeFundamentalInfo my_type_fundamental_info = { 0 };

/* Register a fundamental type */

GType my_type_id = g_type_register_fundamental(g_type_fundamental_next(),

"MyFundamentalType", &my_type_info, &my_type_fundamental_info, 0);

/* Print type names */

printf("Type name of int: %s\n", g_type_name(G_TYPE_INT));

printf("Type name of float: %s\n", g_type_name(G_TYPE_FLOAT));

printf("Type name of object: %s\n", g_type_name(G_TYPE_OBJECT));

printf("Type name of my fundamental type: %s\n", g_type_name(my_type_id));

/* Print type id and name of MyFundamentalType */

printf("Type id: %d\n", g_type_from_name("MyFundamentalType"));

printf("Type name: %s\n", g_type_name(g_type_from_name("MyFundamentalType")));

/* Print attributes of MyFundamentalType */

printf("Is fundamental? %s\n", G_TYPE_IS_FUNDAMENTAL(my_type_id) ? "yes" : "no");

printf("Is derived? %s\n", G_TYPE_IS_DERIVED(my_type_id) ? "yes" : "no");

printf("Is interface? %s\n", G_TYPE_IS_INTERFACE(my_type_id) ? "yes" : "no");

printf("Is classed? %s\n", G_TYPE_IS_CLASSED(my_type_id) ? "yes" : "no");

printf("Is instantiatable? %s\n", G_TYPE_IS_INSTANTIATABLE(my_type_id) ? "yes" : "no");

printf("Is derivable? %s\n", G_TYPE_IS_DERIVABLE(my_type_id) ? "yes" : "no");

printf("Is deep derivable? %s\n", G_TYPE_IS_DEEP_DERIVABLE(my_type_id) ? "yes" : "no");

printf("Is abstract? %s\n", G_TYPE_IS_ABSTRACT(my_type_id) ? "yes" : "no");

printf("Is value abstract? %s\n", G_TYPE_IS_VALUE_ABSTRACT(my_type_id) ? "yes" : "no");

printf("Is value type: %s\n", G_TYPE_IS_VALUE_TYPE(my_type_id) ? "yes" : "no");

printf("Has value table: %s\n", G_TYPE_HAS_VALUE_TABLE(my_type_id) ? "yes" : "no");

return 0;

}

My fundamental type is created by calling g_type_register_fundamental() function. A GTypeInfo and a GTypeFundamentalInfo struct are passed as parameters. And here comes the linux Makefile. You can use pkg-config to replace my include and lib paths:

CC      := gcc
CFLAGS  := -ansi -Wall
INCPATH := -I/usr/include/glib-2.0 -I/usr/lib/glib-2.0/include
LIBS    := -lgobject-2.0
TARGET  := TestGObject1
OBJS    := main.o

all: $(OBJS)
    $(CC) $(CFLAGS) ${LIBS} $(OBJS) -o $(TARGET)

%.o: %.c
    $(CC) $(CFLAGS) $(INCPATH) -c $<

clean:
    rm -f *~
    rm -f *.o
    rm -f $(TARGET)

CC := gcc

CFLAGS := -ansi -Wall

INCPATH := -I/usr/include/glib-2.0 -I/usr/lib/glib-2.0/include

LIBS := -lgobject-2.0

TARGET := TestGObject1

OBJS := main.o

all: $(OBJS)

$(CC) $(CFLAGS) ${LIBS} $(OBJS) -o $(TARGET)

%.o: %.c

$(CC) $(CFLAGS) $(INCPATH) -c $<

clean:

rm -f *~

rm -f *.o

rm -f $(TARGET)

NOTE: REPLACE THE WHITESPACE WITH TAB IN MAKEFILES, IF YOU COPY THE CODE DIRECTLY.

The fundamental type is of no use at all presently. In the next article, I will extend my code to add class meta info.

All source code is available in my skydrive: http://cid-481cbe104492a3af.office.live.com/browse.aspx/share/dev/TestOO. In the TestGObject-{date}.zip/TestGObject1 folder.

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