Array-like statement with curly brackets - what is the purpose?

Question

I found this snippet of code online and I was wondering what it does:

$k[$i] = ord($key{$i}) & 0x1F;

I know that ord() returns an ASCII value, but I'm unclear on what the curly brackets do $key{$i} and also what this does & 0x1F.

Answer 1

That's not an array syntax. It's for accessing single characters from strings only. The index must be numeric.

 $str{1} == $str[1]

It's briefly mentioned here in the info box: http://www.php.net/manual/en/language.types.string.php#language.types.string.substr

Also, it's officially declared deprecated. It has been on and off supposed deprecation in the manual, but is still very valid, if uncommon, syntax.

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The & 0x1F is a bit-wise AND. In this case it limits the decimal values to 0 till 31.

Answer 2

In PHP, either [square brackets] or {curly braces} are fully legal, interchangeable means of accessing an array:

Note: Both square brackets and curly braces can be used interchangeably for accessing array elements (e.g. $array[42] and $array{42} will both do the same thing in the example above).

Source: http://www.php.net/manual/en/language.types.array.php

Both are fully valid; curly braces are not deprecated.

Concerning "& 0x1F", others like @Tadek have responded:

& is a binary operator. See more in the documentation [http://www.php.net/manual/en/language.operators.bitwise.php]. It sets the bits if they are set in both variables.

Answer 3

First part of your question: curly braces

This is about referencing the value of the variable.

In your example, if $i is equal to 123, then

$k[$i] = ord($key{$i}) & 0x1F;

will be the same as

$k[123] = ord($key[123]) & 0x1F;

Second part of your question: '&' sign

& is a binary operator. See more in the documentation. It sets the bits if they are set in both variables.