To create a variable x with the value 12345 in PHP, we do the following:
<?php
$x = 12345;
?>
But let's say that we wrote $x; without assigning it a value:
<?php
$x;
?>
Does the above code causes anything to happen, or does PHP treat the above $x; as non-existent? for example is the above code effectively the same as the following empty code?:
<?php
?>
<?php
$x;
?>
These line of code mean you just initialize a variable name called x. but you doesn't assign value. But it will use some memory.
You can check use of memory:
<?php
$x;
echo memory_get_usage($x);
?>
Your Empty CODE :
<?php
?>
These line of code means you just initialize PHP script. But inside there is nothing actually. But it also use some memory.
You can check use of memory:
<?php
echo memory_get_usage();
?>
Hope you understand the difference.
If you look at what are the defined variables in the following script...
print_r(get_defined_vars());
$x;
print_r(get_defined_vars());
$x = 1;
print_r(get_defined_vars());
You can see that just using $x; doesn't define the variable, it only shows up after assigning it a value. So effectively this is the same as doing nothing.
Also checking the opcodes being generated...
With $x=1; - phpdbg -p* a.php
function name: (null)
L1-4 {main}() /home/nigel/a.php - 0x7f2f36c8e000 + 3 ops
L3 #0 EXT_STMT
L3 #1 ASSIGN $x 1
L4 #2 RETURN<-1> 1
with $x; - phpdbg -p* a.php
function name: (null)
L1-4 {main}() /home/nigel/a.php - 0x7f5898079050 + 2 ops
L4 #0 EXT_STMT
L4 #1 RETURN<-1> 1
So it looks as though no opcode is generated.