Is there a logical explanation to this?
<?php
$$a = 'hello world';
echo $$a; //displays hello world
echo $$aa; //displays hello world
echo $$aaa; //displays hello world
?>
Source: Tips4all
Source: Tips4all
I have a 2.67 GHz Celeron processor, 1.21 GB of RAM on a x86 Windows XP Professional machine. My understanding is that the Android emulator should start fairly quickly on such a machine, but for me it does not. I have followed all instructions in setting up the IDE, SDKs, JDKs and such and have had some success in staring the emulator quickly but is very particulary. How can I, if possible, fix this problem?
if you try
ReplyDelete$$a = 'hello world';
echo $$a; //displays hello world
echo $$aa; //displays hello world
echo $$aaa; //displays hello world
die( "<pre>" . print_r( get_defined_vars(), true ) . "</pre>" );
You can see that it has registed a variable with no name so yes, according to PHP's naming conventions, this would be a bug
When doing
ReplyDelete$$a = 'foo';
you are saying take the value of $a. Convert it to string. Use the String as variable name to assign 'foo' to it. Since $a is undefined and returns NULL, which when typecasted to String is '', you are assigning the variable ${''};
echo ${''}; // 'foo'
Ironically, you can do
${''} = 'foo'; /* but not */ $ = 'foo';
And you can do
${''} = function() { return func_get_arg(0); };
echo ${''}('Hello World');
// or
echo $$x('Hello World');
which would trigger a notice about $x being undefined but output Hello World then. Funny enough, the following doesnt work:
${''} = function() { return func_get_arg(0); };
echo $x('Hello World');
Because it triggers Fatal error: Function name must be a string. Quirky :D
Since the PHP manual says
Variable names follow the same rules as other labels in PHP. A valid variable name starts with a letter or underscore, followed by any number of letters, numbers, or underscores.
I'd consider being able to assign an empty named variable a bug indeed.
There is a somewhat related bug filed for this already:
http://bugs.php.net/bug.php?id=39150
I'm betting that it's defining the variable as something to the effect of ${''}, or a variable with no name, or something along those lines.
ReplyDeleteSince neither $a nor $aa nor $aaa are defined, they all point to the same funky, blank variable name when used in a variable variable context.
Well, if $a is empty, then you're setting an empty variable name to = 'hello world'... So then every time you reference that empty variable name, you'll get what's stored there...
ReplyDeleteIt's just like
$a = '';
$$a = 'Foo Bar';
$b = '';
echo $$b; //Displays Foo Bar
You are not getting it right, consider this:
ReplyDelete$a = 'hello';
$hello = "hello again";
echo $$a;
Output:
hello again
In your case, you have not set the value of following variables, so it outputs the same.
Explanation:
When you do $$a, it means:
$ $a;
^ ^
$ used for php vars means a's value that is hello
So it becomes:
$hello
Whose value is:
hello again
set $a first, then you don't have to worry about this bug.
ReplyDelete