signing message problem

[Hajdu Péter]

Hi!

	I've got a problem while signing message with gpgme. I'm really new to 
gpgme, so please be patient. Here is my code:
	
	error = gpgme_data_new_from_file(&message,"./tempfile",1);
	error = gpgme_new( &context );
	gpgme_set_armor( context, 1);
	error = gpgme_op_keylist_start(context,NULL,0);
	gpgme_key_ref( key );
	while ( !(error = gpgme_op_keylist_next (context, &key)) ) {
		printf("%s\n",gpg_strerror(error));
		uid = key->uids;
		str = uid->uid;
		printf("%s\n",str);
		error = gpgme_signers_add( context, key);
		printf("%s\n",gpg_strerror( error ));
		gpgme_key_release( key );
	}
	gpgme_op_keylist_end( context );
	memset(buf,0,sizeof(buf));
	gpgme_data_new(&signature);
	error = gpgme_op_sign( context, message, signature, 
GPGME_SIG_MODE_NORMAL );
  	gpgme_data_release(message);
	printf("%s\n",gpg_strerror( error ));
	memset(buf,0,sizeof(buf));
	printf("%d\n",gpgme_data_read( signature, buf, sizeof(buf) ));
	printf("%s",buf);
	gpgme_data_release(signature);
	gpgme_release(context);
	

That's not the entire code, I've cut out error handling. At the end, 
gpgme_data_read reads 0 data from signature, it looks like it's empty. 
It reads in ./tempfile correctly, and it reads my keys too, and there 
were no errors. I really don't know what's wrong.

Please help, and sorry for my bad english.

Peter Hajdu