Using GIOChannel

GIOChannel provides a portable method for using file descriptors, sockets and pipes and integrating them into the GLib main loop.

The g_io_channel_unix_new() API takes a file descriptor as an input parameter and is used to create a new GIOChannel . Alternatively, the g_io_channel_new_file() API can be used to create a channel for a file. Once the channel is created, it can be used in a generic manner.

To read a channel, APIs such as the following can be used:

• g_io_channel_read_chars()

• g_io_channel_read_line()

• g_io_channel_read_to_end()

To write to a channel an API like g_io_channel_write_chars() is used.

To set the position in the current GIOChannel , g_io_channel_seek_position() can be used.

Finally the channel can be closed using g_io_channel_shutdown() .

The following is an example code where a file descriptor to a plain file is used to create a GIOChannel , and then the contents of the file are read in chunks of 100 bytes and printed using g_print . Finally the channel is closed.

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

int main(int argc, char *argv[])
{
	GIOChannel *channel;
	gchar buf[100];
	gsize bytes_read;
	FILE *fp;
	
	if(argc != 2)
	{
		g_print("usage:cat <file_name>\n");
		g_print("Press any key to exit\n");
		getchar();
		return 1;
	}
	
	fp = fopen(argv[1],"r");
	
	if(!fp)
	{
		g_print("Unable to open the file %s\n",argv[1]);
		return 1;
	}
		
	channel = g_io_channel_unix_new(fileno(fp));
	
 	do
 	{
		g_io_channel_read_chars(channel,buf,100,&bytes_read,NULL);
		g_print("%s",buf);
		
	}
	while(bytes_read > 0);
	
	g_io_channel_shutdown(channel,TRUE,NULL);
	
	fclose(fp);
 
	return 0;
}
     

In the example below, a sample code to copy a file is written. In the code, channels are opened using g_io_channel_new_file() . The contents of the file are read using g_io_channel_read_chars() , and the contents are written to a new file using g_io_channel_write_chars() .

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

int main(int argc, char *argv[])
{
	GIOChannel *in_channel,*out_channel;
	gchar buf[100];
	gsize bytes_read,bytes_written;
	GError *error = NULL;
	
	if(argc != 3)
	{
		g_print("usage:<cp SOURCE> <DESTINATION>\n");
		g_print("Press any key to exit\n");
		getchar();
		return 1;
	}
		
	in_channel = g_io_channel_new_file(argv[1],"r",&error);
	
	if(!in_channel)
	{
		g_print("Unable to open the file %s to read\n",argv[1]);
		g_print("Press any key to exit\n");
		getchar();
		return 1;
	}
	
	out_channel = g_io_channel_new_file(argv[2],"w",&error);
	
	if(!out_channel)
	{
		g_print("Unable to open the file %s to write\n",argv[2]);
		g_print("Press any key to exit\n");
		getchar();
		return 1;
	}
	
	do
	{
		g_io_channel_read_chars(in_channel,buf,100,&bytes_read,&error);
		if(error)
		{
			g_print("Error while reading file %s\n",argv[1]);
			g_print("Press any key to exit\n");
			getchar();
			return 1;
		}
		
		g_io_channel_write_chars(out_channel,buf,bytes_read,&bytes_written,&error);
		if(error)
		{
			g_print("Error while writing file %s\n",argv[2]);
			g_print("Press any key to exit\n");
			getchar();
			return 1;
		}
	}
	while(bytes_read > 0);
	
       g_io_channel_shutdown(in_channel,TRUE,&error);
	if(error)
	{
		g_print("Error has occured\n");
		g_print("Press any key to exit\n");
		getchar();
		return 1;
	}
	 
	g_io_channel_shutdown(out_channel,TRUE,&error);
 	if(error)
	{
		g_print("Error has occured\n");
		g_print("Press any key to exit\n");
		getchar();
		return 1;
	}
	
	g_print("File copied successfully...\n");
	getchar();
	
	return 0;
}
     

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

int fd[2];

void *thread_function(void *data)
{
	// call sleep so that the main loop source is not ready immediately
	sleep(10);
	
	write(fd[1],"GIOChannel main loop example",29);
	return NULL;
}

gboolean my_callback(GIOChannel *source,GIOCondition condition,gpointer data)
{
	char buf[100];	
	
	read(fd[0],buf,sizeof(buf));
	g_print("%s",buf);
	
	getchar();
	
	g_main_loop_quit((GMainLoop *)data);
	
	return FALSE;
}

int main()
{
	GMainLoop *loop;
	GIOChannel *channel;
	
	pipe(fd);
	
	channel = g_io_channel_unix_new(fd[0]);
	
	g_thread_init(NULL);
	g_thread_create(thread_function,NULL,TRUE,NULL);
	
	loop = g_main_loop_new(NULL,FALSE);
	g_io_add_watch(channel,G_IO_IN | G_IO_HUP | G_IO_ERR,(GIOFunc)my_callback,loop);
	g_main_loop_run(loop);
	
	g_io_channel_shutdown(channel,TRUE,NULL);

	return 0;
}