[RESOLVED] Double quote, single quote, no quote

[fr600]

What's the difference? For example,

$res = mysql_query("SELECT * FROM members");
$row = mysql_fetch_array($res);

$username = $row[username];
$username = $row['username'];
$username = $row["username"];

What's the difference between these 3 usernames?

[bretticus]

$username = $row[username];

will work if username is a constant or a string key (the php manual says using this for string keys is deprecated and WRONG.)

$username = $row['username'];

this is just the same as

$username = $row["username"];  

You can insert variables into strings quoted with double quotes such as

$username = $row["username$i"];  

where you cannot with single-quotes. however

$username = $row['username' . $i];  

is equivalent.

Code convention typically uses the form

$username = $row['username'];