Variables in PHP

Variables in PHP

<?php
$var = 'Bob';
$Var = 'Joe';
echo "$var, $Var";      // outputs "Bob, Joe"

$4site = 'not yet';     // invalid; starts with a number
$_4site = 'not yet';    // valid; starts with an underscore
$täyte = 'mansikka';    // valid; 'ä' is (Extended) ASCII 228.
?>
  • Variables in PHP are represented by a dollar sign followed by the name of the variable.
  • The variable name is case-sensitive.
  • 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.
  • By default, variables are always assigned by value.
  • PHP also offers another way to assign values to variables: assign by reference.
  • It is not necessary to initialize variables in PHP however it is a very good practice.
  • Uninitialized variables have a default value of their type depending on the context in which they are used - booleans default to FALSE, integers and floats default to zero, strings (e.g. used in echo) are set as an empty string and arrays become to an empty array.
  • Relying on the default value of an uninitialized variable is problematic in the case of including one file into another which uses the same variable name.

Assign by reference

<?php
$foo = 'Bob';              // Assign the value 'Bob' to $foo
$bar = &$foo;              // Reference $foo via $bar.
$bar = "My name is $bar";  // Alter $bar...
echo $bar;
echo $foo;                 // $foo is altered too.
?>
  • This means that the new variable simply references (in other words, "becomes an alias for" or "points to") the original variable.
  • Changes to the new variable affect the original, and vice versa.
  • To assign by reference, simply prepend an ampersand (&) to the beginning of the variable which is being assigned (the source variable).
  • Only named variables may be assigned by reference.

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