十万火急.....

...
<?php
$str = iconv("ISO-8859-1", "gb2312", "一帆风顺");
echo "string is:".$str;
?>
...
执行时提示错误:
Warning: iconv: cannot convert from `ISO-8859-1' to `gb2312'in
program.
怎么会这样啊？那位高手帮忙看看吧，在这里先谢谢了！