Default socket path for programs linked with libmariadbclient.a

When I try to connect to mariadb server with program linked with libmariadbclient.a over local connection, then it reports:
mysql_real_connect:Can't connect to local MySQL server through socket '/tmp/mysql.sock'
My mysql setup in /etc/mysql/my.cnf uses:
socket = /run/mysqld/mysqld.sock
for [client] and [mysqld] section.
Howto setup connection in C program to use default socket path from
/etc/mysql/my.cnf ?