Syntax error with select statement

Hello,
I have problem with select statement in c++ program I am using pqxx library to connect to postgresql database.My query is

result R(T.exec(" select * from dbtable where username = ' "+user+" ' and password = ' "+st+" ' "));

here st is in encrypted format and the string is st = M^fuo|`sjyo|`so|>-?z this is the string i stored in the table .

The error I was encountered is "terminate called after throwing an instance of 'pqxx::syntax_error'
what(): ERROR: unterminated quoted string at or near "'M^fuo|`sjyo|`so|>-?z"
LINE 1: ...table where username = 'achandana' and password = 'M^fuo|`sj...
^ "

I am not able to identify what the actual problem is can you guys please help to solve this problem?Your help is greatly appreciated.

Thank You,
Aravind.
^