Probléme avec sprintf() sous linux

Salut,
j'ai un probléme dans mon code en gcc sous linux.
lors de la compilation j'obtient les messages suivants:
"access_log.c:1033: warning: left-hand operand of comma expression has no effect
access_log.c:1033: warning: left-hand operand of comma expression has no effect
access_log.c:1033: warning: left-hand operand of comma expression has no effect
access_log.c:1033: warning: statement with no effect
access_log.c:1039: warning: left-hand operand of comma expression has no effect
access_log.c:1039: warning: left-hand operand of comma expression has no effect
access_log.c:1039: warning: left-hand operand of comma expression has no effect
access_log.c:1039: warning: statement with no effect
access_log.c:1044: warning: left-hand operand of comma expression has no effect
access_log.c:1044: warning: left-hand operand of comma expression has no effect
access_log.c:1044: error: wrong type argument to unary plus"
La partie du code de la ligne 1033 jusq'au 1044 est la suivante:
" sprintf(req,"select * from connection where sec='%9ld' and usec='%03d'",(long int) current_time.tv_sec, (int) current_time.tv_usec / 1000);
mysql_query(conn,req);
result = mysql_store_result(conn);
num = mysql_num_rows(result);
if (num== 0)
{
sprintf(req,"insert into connection values('%9ld','%03d')",(long int) current_time.tv_sec,(int) current_time.tv_usec / 1000);
mysql_query(conn,req);mysql_commit(conn);}
// on libère la mémoire prise pour les résultats

mysql_free_result(result);
sprintf(req,"select * from client where adr_IP_client ='%s'",client);"
quelqu'un peut maider SVP.
merci d'avace.