why can't access table by field name in c/c++ API

[james cao]

int f1,f2;
MYSQL_RES *res;
MYSQL_ROW row;
cstring strSql = "select field1,field2 from mytable";

mysql_query(&m_pDBConn, strSql);
res = mysql_store_result(&m_pDBConn);
row = mysql_fetch_row(res);
......

In mysql 5.01(c/c++ API), Why can't access the table with field name?
f1 = row["field1"];
f2 = row["field2"];

We must do it by:
f1 = row[0];
f2 = row[1];

.......