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phpvariablesconditional-statements
caw
caw

Reputation: 31487

PHP: Variable empty or not set or what?

What is the difference between these four PHP statements?

if (isset($data)) {

if (!empty($data)) {

if ($data != '') {

if ($data) {

Do they all do the same?

Upvotes: 12

Views: 30532

Answers (4)

jlb
jlb

Reputation: 20010

Check PHP manual out: http://www.php.net/manual/en/types.comparisons.php

Expression  gettype() empty() is_null() isset() if($x)
$x = "";        string  TRUE    FALSE   TRUE    FALSE
$x = null;      NULL    TRUE    TRUE    FALSE   FALSE
var $x;         NULL    TRUE    TRUE    FALSE   FALSE
$x undefined    NULL    TRUE    TRUE    FALSE   FALSE
$x = array();   array   TRUE    FALSE   TRUE    FALSE
$x = false;     boolean TRUE    FALSE   TRUE    FALSE
$x = true;      boolean FALSE   FALSE   TRUE    TRUE
$x = 1;         integer FALSE   FALSE   TRUE    TRUE
$x = 42;        integer FALSE   FALSE   TRUE    TRUE
$x = 0;         integer TRUE    FALSE   TRUE    FALSE
$x = -1;        integer FALSE   FALSE   TRUE    TRUE
$x = "1";       string  FALSE   FALSE   TRUE    TRUE
$x = "0";       string  TRUE    FALSE   TRUE    FALSE
$x = "-1";      string  FALSE   FALSE   TRUE    TRUE
$x = "php";     string  FALSE   FALSE   TRUE    TRUE
$x = "true";    string  FALSE   FALSE   TRUE    TRUE
$x = "false";   string  FALSE   FALSE   TRUE    TRUE

As you can see, if(!empty($x)) is equal to if($x) and if(!is_null($x)) is equal to if(isset($x)). As far as if $data != '' goes, it is TRUE if $data is not NULL, '', FALSE or 0 (loose comparison).

Upvotes: 25

meder omuraliev
meder omuraliev

Reputation: 186692

They aren't the same.

  1. true if the variable is set. the variable can be set to blank and this would be true.

  2. true if the variable is set and does not equal empty string, 0, '0', NULL, FALSE, blank array. it is clearly not the same as isset.

  3. if the variable does not equal an empty string, if the variable isnt set its an empty string.

  4. if the variable coerces to true, if the variable isnt set it will coerce to false.

Upvotes: 4

Skawful
Skawful

Reputation: 9917

if (isset($data)) - Determines if a variable is set (has not bet 'unset()' and is not NULL.

if (!empty($data)) - Is a type agnostic check for empty if $data was '', 0, false, or NULL it would return true.

if ($data != '') { this is a string type safe of checking whether $data is not equal to an empty string

if ($data) { this is a looking for true or false (aka: 0 or 1)

Upvotes: 0

hsz
hsz

Reputation: 152284

if (isset($data)) {

Variable is just set - before that line we declared new variable with name 'data', i.e. $data = 'abc';

if (!empty($data)) {

Variable is filled with data. It cannot have empty array because then $data has array type but still has no data, i.e. $data = array(1); Cannot be null, empty string, empty array, empty object, 0, etc.

if ($data != '') {

Variable is not an empty string. But also cannot be empty value (examples above).
If we want to compare types, use !== or ===.

if ($data) {

Variable is filled out with any data. Same thing as !empty($data).

Upvotes: 10

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