Calling dbus with C and glib

this example calls method GetStatus on interface org.freesmartphone.GSM.Network specially for the property "provider"

/* author: Matze Huber matthias.huber [AT] wollishausen.de */
/* License: GPL Latest */ 
/* less than half of the time could be necessary, if dbus-calls and result-types and their usage were better documented */

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>

#include <dbus/dbus-glib.h>
#include <glib-object.h>
#include <glib.h>

static char provider[40];
static char netstring[128];


static DBusGConnection *connection = NULL;
DBusGProxy *proxy_dbus = NULL;
GError *error = NULL;

int main( int argc, char *argv[] ) {
static DBusGProxyCall *id;
GHashTable *hash = NULL;
int i;

	g_type_init ();

	connection = dbus_g_bus_get(DBUS_BUS_SYSTEM, &error);
	if (!connection) {
		fprintf(stderr, "Failed to open connection to system bus: %s", error->message);
		exit(1);
	}
	proxy_dbus = dbus_g_proxy_new_for_name(connection, "org.freesmartphone.ogsmd", "/org/freesmartphone/GSM/Device", "org.freesmartphone.GSM.Network");

	hash = g_hash_table_new(NULL, NULL);

	if ( !dbus_g_proxy_call( proxy_dbus, "GetStatus", &error, 
		G_TYPE_INVALID, 
		dbus_g_type_get_map ("GHashTable", G_TYPE_STRING, G_TYPE_VALUE), &hash, G_TYPE_INVALID ) ) { 
		if ( error && error->message )
	                fprintf(stderr, "error at line %d: %s\n", __LINE__, error->message);
		else if ( error )
	                fprintf(stderr, "error at line %d\n", __LINE__);
		else
			fprintf(stderr, "error at line: %d\n", __LINE__);
	}
	else {
		fprintf(stderr, "provider: %s\n", g_value_get_string(g_hash_table_lookup(hash, "provider")));
	}
	return 0;
}