In where shall I use isset and empty

Question

I read somewhere that the isset   function treats an empty string as TRUE  therefore isset   is not an effective way to validate text inputs and text boxes from a HTML form   So you can use empty   to check that a user typed something    Is it true that the isset   function treats an empty string as TRUE  Then in which situations should I use isset    Should I always use  empty   to check if there is something    For example instead of   if isset   GET  gender          Using this  if  empty   GET  gender

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isset   tests if a variable is set and not null   http   us php net manual en function isset php  empty   can return true when the variable is set to certain values   http   us php net manual en function empty php   lt  php   the var   0   if  isset  the var       echo  set     else     echo  not set      echo   n    if  empty  the var       echo  empty     else     echo  not empty       gt

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isset is used to determine if an instance of something exists that is  if a variable has been instantiated    it is not concerned with the value of the parameter     Pascal MARTIN     1      empty   does not generate a warning if the variable does not exist    therefore  isset   is preferred when testing for the existence of a variable when you intend to modify it

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I came here looking for a quick way to check if a variable has any content in it  None of the answers here provided a full solution  so here it is     It s enough to check if the input is    or null  because   Request URL     test php var  results in   GET  var         Request URL     test php results in   GET  var     null    isset   returns false only when the variable exists and is not set to null  so if you use it you ll get true for empty strings        empty   considers both null and    empty  but it also considers  0  empty  which is a problem in some use cases   If you want to treat  0  as empty  then use empty    Otherwise use the following check    var            evaluates to false only for the following inputs       null false   I use the following check to also filter out strings with only spaces and line breaks   function hasContent  var       return trim  var

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I use the following to avoid notices  this checks if the var it s declarated on GET or POST and with the   prefix you can safely check if is not empty and avoid the notice if the var is not set   if  isset   GET  var     amp  amp     GET  var                Is not empty  do something

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empty will do the trick  if you need only to check data exists or not then use isset other empty can handle other validations   lt  php  array      name new    gt   print me     if   empty  array  name         echo  array  name         output    nothing                                                                          array2      name    gt  NULL    if   empty  array2  name         echo  array2  name         output    nothing                                                                          array3      name    gt        if   empty  array3  name         echo  array3  name         output    nothing                                                                            array4    1 2    if   empty  array4  name         echo  array4  name         output    nothing                                                                          array5        if   empty  array5  name         echo  array5  name         output    nothing

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isset   vs empty   vs is null

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isset vs   empty  FTA       isset   checks if a variable has a   value including  False  0 or empty   string   but not NULL  Returns TRUE   if var exists  FALSE otherwise       On the other hand the empty   function   checks if the variable has an empty   value empty string  0  NULL or   False  Returns FALSE if var has a   non-empty and non-zero value

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isset   is used to check if the variable is set with the value or not and Empty   is used to check if a given variable is empty or not   isset   returns true when the variable is not null whereas Empty   returns true if the variable is an empty string

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isset  variable         variable     null  empty  variable         variable    false

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Neither is a good way to check for valid input    isset   is not sufficient because     as has been noted already      it considers an empty string to be a valid value    empty   is not sufficient either because it rejects  0   which could be a valid value    Using isset   combined with an equality check against an empty string is the bare minimum that you need to verify that an incoming parameter has a value without creating false negatives   if  isset   GET  gender    and    GET  gender                        But by  bare minimum   I mean exactly that   All the above code does is determine whether there is some value for   GET  gender     It does not determine whether the value for   GET  gender   is valid  e g   one of   Male    Female   FileNotFound      For that  see Josh Davis s answer

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Please consider behavior may change on different PHP versions From documentation isset   Returns TRUE if var exists and has any value other than NULL  FALSE otherwise https   www php net manual en function isset php empty   does not exist or if its value equals FALSE https   www php net manual en function empty php  empty  x       isset  x       x      returns true    empty  x      isset  x   amp  amp   x      returns true

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isset is intended to be used only for variables and not just values  so isset  foobar   will raise an error  As of PHP 5 5  empty supports both variables and expressions   So your first question should rather be if isset returns true for a variable that holds an empty string  And the answer is    var       var dump isset  var      The type comparison tables in PHP   s manual is quite handy for such questions   isset basically checks if a variable has any value other than null since non-existing variables have always the value null  empty is kind of the counter part to isset but does also treat the integer value 0 and the string value  0  as empty   Again  take a look at the type comparison tables

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isset   is not an effective way to validate text inputs and text boxes from a HTML form   You can rewrite that as  isset   is not a way to validate input   To validate input  use PHP s filter extension  filter has var   will tell you whether the variable exists while filter input   will actually filter and or sanitize the input   Note that you don t have to use filter has var   prior to filter input   and if you ask for a variable that is not set  filter input   will simply return null

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In the most general way     isset tests if a variable  or an element of an array  or a property of an object  exists  and is not null  empty tests if a variable       contains some non-empty data     To answer question 1     str       var dump isset  str      gives  boolean true   Because the variable  str exists    And question 2     You should use isset to determine whether a variable exists   for instance  if you are getting some data as an array  you might need to check if a key isset in that array  Think about   GET     POST  for instance   Now  to work on its value  when you know there is such a value   that is the job of empty

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var          Evaluates to true because  var is empty if   empty  var      echo   var is either 0  empty  or not set at all        Evaluates as true because  var is set if   isset  var       echo   var is set even though it is empty           Source  Php net

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When and how to use    isset     True for 0  1  empty string  a string containing a value  true  false  False for null  e g    status   0 if  isset  status      True  status   null  if  isset  status      False    Empty   False for 1  a string containing a value  true  True for null  empty string  0  false e g   status   0 if empty  status      true  status   1 if empty  status      False

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Using empty is enough   if  empty  variable           Do stuff     Additionally  if you want an integer value it might also be worth checking that intval  variable      FALSE

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If you have a   POST  param   and assume it s string type then  isset   POST  param     amp  amp    POST  param          amp  amp    POST  param       0    is identical to    empty   POST  param

[php] In where shall I use isset() and !empty()

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