PQconnectdb question and md5 password

Hello,

I don't know how can I pass a md5 password to the password field ?
example :
connInfo = "host=localhost port=5432 dbname=db_stats user=postgres
password=secret";
  pConn = PQconnectdb(connInfo);

I try to replace the string 'secret' by the content of /etc/shadow but
without succès.

Thanks in advance

Guy