c++ convert wchar_t to UTF-8 for DB

Hello all,
I write with reference to the message readable at
http://www.postgresql.org/message-id/4BF575E6.5060203@hogranch.com

I am in the situation described in the message. I have a char* in C++ and i want to put in my db, but most of the non ASCII charachers are broken.
So i used wchar_t, but the following function doesn't exist:

PGresult *PQexec(PGconn *conn, const wchar_t *query);

In the message I referred at the beginning of this e-mail, one the answer is clear about what to do (convert wchar_t to UTF-8), but it's not explained how to do that.
I am doing this on Linux.

Thanks,
Francesco F.

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