PHP code snippets: variables

isset()

isset($var) returns TRUE if the variable $var is a declared value and its value is different from NULL. Otherwise, it returns FALSE.

<!DOCTYPE html>
<html>
<head>
  <meta content="text/html;charset=utf-8" http-equiv="Content-Type">
  <title>isset</title>
</head>
<body>

  <?php


     $var_foo   =  "foo";
     $var_2     =     2 ;
     $var_      =    "" ;
     $var_0     =     0 ;
     $var___    =  "  " ;
     $var_null  =  null ;


     if ( isset ($var_foo  ) ) print "var_foo  is set<br>"; else print "var_foo  is <b>not</b> set<br>"; // var_foo is set
     if ( isset ($var_2    ) ) print "var_2    is set<br>"; else print "var_2    is <b>not</b> set<br>"; // var_2 is set
     if ( isset ($var_     ) ) print "var_     is set<br>"; else print "var_     is <b>not</b> set<br>"; // var_ is set
     if ( isset ($var_0    ) ) print "var_0    is set<br>"; else print "var_0    is <b>not</b> set<br>"; // var_0 is set
     if ( isset ($var___   ) ) print "var___   is set<br>"; else print "var___   is <b>not</b> set<br>"; // var___ is set
     if ( isset ($var_null ) ) print "var_null is set<br>"; else print "var_null is <b>not</b> set<br>"; // var_null is not set
     if ( isset ($var_na   ) ) print "var_na   is set<br>"; else print "var_na   is <b>not</b> set<br>"; // var_na is not set

     unset ($var_2);

     if ( isset ($var_2    ) ) print "var_2    is set<br>"; else print "var_2    is <b>not</b> set<br>"; // var_2 is not set

  ?>

</body>
</html>

Github repository about-php, path: /isset.html

Compare with empty().

In order to check if a key exists in a associative array, the function array_key_exists() can be used.

var_dump()

var_dump() shows information about one or more variables.

<!DOCTYPE html>
<html>
<head>
  <meta content="text/html;charset=utf-8" http-equiv="Content-Type">
  <title>array_key_exists</title>
</head>
<body>

<pre>
<?php

   $num = 42;
   $txt ='Hello world';
   $ary =['foo', 'bar', 'baz'];
   $dct =['num' => 99, 'txt' => 'ciao'];

   var_dump($num, $txt, $ary, $dct);

?>
</pre>

</body>
</html>

Github repository about-php, path: /variable/var_dump.html

This example prints

int(42)
string(11) "Hello world"
array(3) {
  [0]=>
  string(3) "foo"
  [1]=>
  string(3) "bar"
  [2]=>
  string(3) "baz"
}
array(2) {
  ["num"]=>
  int(99)
  ["txt"]=>
  string(4) "ciao"
}

PHP code snippets: variables

isset()

var_dump()

See also