try or adapt this:

pStatement = "{?=call MyProc(?)}";

//return value parameter

rc = SQLBindParameter(hstmt, 1, SQL_PARAM_OUTPUT, SQL_C_SLONG, SQL_INTEGER,

   11, 0, (void*)&m_lDbOutParam, 0, &m_lBufLength);

//1st parameter value

rc = SQLBindParameter(hstmt, 2, SQL_PARAM_INPUT,...