using no quotes vs single quotes vs double quotes in $_POST value

Question

Possible Duplicate:
Should I use php quote escapes for single quotes or use double quotes in arrays?
Is it okay to use array[key] in PHP?

what is the difference between these three $_POST values? :

$_POST[data];

$_POST['data'];

$_POST["data"];

Answer 1

The first one, the index is the constant data. Since that is likely undefined, PHP will often just convert it to the string 'data' and log a warning message.

The second two are both identical. The index is the string 'data'.

Answer 2

[Short addendum, since this is a dupe.]

This is considered technically wrong, unless a constant foo had been defined.

 print $_POST[data];

Only in double quoted context it is valid (actually required sans curly quotes) to leave out the array keys:

 print " use $_POST[data] in double quote context";

Btw, also check the manual (it can also be freely downloaded!) on these topics:

• http://php.net/manual/en/language.types.string.php
• http://php.net/manual/en/language.types.array.php

Answer 3

You are taking it slightly wrong.

These quotes has nothing to with "POST value".
You can use almost any PHP expression as an array key - a string, a variable, a constnt, a function call.

I your case these keys being regular PHP strings. And as a string it ought to be quoted - that's all

As for the quotes - there is no difference in this case.
Double quotes accept some special characters to interpret, you can see the list in the manual.
But as there are no special characters in your strings - there is no difference, which quotes to use.