Why this code fails

Hi,
Following code fails with the error "Invalid column nuber in DescribeCol".

I'm trying to run it with the iODBC DM and the official PG ODBC driver.

[code]
int ODBCDatabase::AskPostgresForLogFile()
{
    int result = 0;
    SQLWCHAR *columnName = new SQLWCHAR[256], *columnData;
    SQLSMALLINT columnNameLen, columnDataType, columnDataDigits,
columnDataNullable;
    SQLLEN columnDataLen;
    SQLULEN columnDataSize;
    std::wstring query = L"SHOW log_directory";
    std::vector<std::wstring> errorMsg;
    SQLWCHAR *qry = new SQLWCHAR[query.length() + 2];
    memset( qry, '\0', query.length() + 2 );
    uc_to_str_cpy( qry, query );
    RETCODE ret = SQLAllocHandle( SQL_HANDLE_STMT, m_hdbc, &m_hstmt );
    if( ret == SQL_SUCCESS || ret == SQL_SUCCESS_WITH_INFO )
    {
        ret = SQLPrepare( m_hstmt, qry, SQL_NTS );
        if( ret != SQL_SUCCESS && ret != SQL_SUCCESS_WITH_INFO )
        {
            GetErrorMessage( errorMsg, 1 );
            result = 1;
        }
        else
        {
            ret = SQLDescribeCol( m_hstmt, 1, columnName, 256,
&columnNameLen, &columnDataType, &columnDataSize, &columnDataDigits,
&columnDataNullable );
            if( ret != SQL_SUCCESS && ret != SQL_SUCCESS_WITH_INFO )
            {
                GetErrorMessage( errorMsg, 1 );
                result = 1;
            }
            else
            {
            }
}
[/code]

Thank you.