How do the PHP equality double equals and identity triple equals comparison operators differ

Question

What is the difference between    and       How exactly does the loosely    comparison work  How exactly does the strict     comparison work   What would be some useful examples

User · Answer

You would use     to test whether a function or variable is false rather than just equating to false  zero or an empty string     needle    a    haystack    abc    pos   strpos  haystack   needle   if   pos     false        echo  needle     was not found in      haystack    else       echo  needle     was found in      haystack     at location      pos      In this case strpos would return 0 which would equate to false in the test  if   pos    false    or  if    pos    which is not what you want here

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Difference between    and      The difference between the loosely    equal operator and the strict     identical operator is exactly explained in the manual      Comparison Operators    ----------------------------------------------------------------------------------     Example     Name         Result                                                        ---------- ----------- -----------------------------------------------------------      a      b    Equal        TRUE if  a is equal to  b after type juggling                   a      b    Identical    TRUE if  a is equal to  b  and they are of the same type      ----------------------------------------------------------------------------------       Loosely    equal comparison  If you are using the    operator  or any other comparison operator which uses loosely comparison such as      lt  gt  or     you always have to look at the context to see what  where and why something gets converted to understand what is going on   Converting rules   Converting to boolean Converting to integer Converting to float Converting to string Converting to array Converting to object Converting to resource Converting to NULL   Type comparison table  As reference and example you can see the comparison table in the manual      Loose comparisons with      -----------------------------------------------------------------------------------------------------------                TRUE     FALSE      1        0       -1        1        0       -1      NULL     array       php               --------- ------- ------- ------- ------- ------- ------- ------- ------- ------- --------- ------- -------      TRUE       TRUE     FALSE    TRUE     FALSE    TRUE     TRUE     FALSE    TRUE     FALSE    FALSE      TRUE     FALSE       FALSE      FALSE    TRUE     FALSE    TRUE     FALSE    FALSE    TRUE     FALSE    TRUE     TRUE       FALSE    TRUE        1          TRUE     FALSE    TRUE     FALSE    FALSE    TRUE     FALSE    FALSE    FALSE    FALSE      FALSE    FALSE       0          FALSE    TRUE     FALSE    TRUE     FALSE    FALSE    TRUE     FALSE    TRUE     FALSE      TRUE     TRUE        -1         TRUE     FALSE    FALSE    FALSE    TRUE     FALSE    FALSE    TRUE     FALSE    FALSE      FALSE    FALSE        1         TRUE     FALSE    TRUE     FALSE    FALSE    TRUE     FALSE    FALSE    FALSE    FALSE      FALSE    FALSE        0         FALSE    TRUE     FALSE    TRUE     FALSE    FALSE    TRUE     FALSE    FALSE    FALSE      FALSE    FALSE        -1        TRUE     FALSE    FALSE    FALSE    TRUE     FALSE    FALSE    TRUE     FALSE    FALSE      FALSE    FALSE       NULL       FALSE    TRUE     FALSE    TRUE     FALSE    FALSE    FALSE    FALSE    TRUE     TRUE       FALSE    TRUE        array      FALSE    TRUE     FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    TRUE     TRUE       FALSE    FALSE        php       TRUE     FALSE    FALSE    TRUE     FALSE    FALSE    FALSE    FALSE    FALSE    FALSE      TRUE     FALSE                  FALSE    TRUE     FALSE    TRUE     FALSE    FALSE    FALSE    FALSE    TRUE     FALSE      FALSE    TRUE      -----------------------------------------------------------------------------------------------------------     Strict     identical comparison  If you are using the     operator  or any other comparison operator which uses strict comparison such as     or      then you can always be sure that the types won t magically change  because there will be no converting going on  So with strict comparison the type and value have to be the same  not only the value   Type comparison table  As reference and example you can see the comparison table in the manual      Strict comparisons with       -----------------------------------------------------------------------------------------------------------                TRUE     FALSE      1        0       -1        1        0       -1      NULL     array       php               --------- ------- ------- ------- ------- ------- ------- ------- ------- ------- --------- ------- -------      TRUE       TRUE     FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE      FALSE    FALSE       FALSE      FALSE    TRUE     FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE      FALSE    FALSE       1          FALSE    FALSE    TRUE     FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE      FALSE    FALSE       0          FALSE    FALSE    FALSE    TRUE     FALSE    FALSE    FALSE    FALSE    FALSE    FALSE      FALSE    FALSE       -1         FALSE    FALSE    FALSE    FALSE    TRUE     FALSE    FALSE    FALSE    FALSE    FALSE      FALSE    FALSE        1         FALSE    FALSE    FALSE    FALSE    FALSE    TRUE     FALSE    FALSE    FALSE    FALSE      FALSE    FALSE        0         FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    TRUE     FALSE    FALSE    FALSE      FALSE    FALSE        -1        FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    TRUE     FALSE    FALSE      FALSE    FALSE       NULL       FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    TRUE     FALSE      FALSE    FALSE       array      FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    TRUE       FALSE    FALSE        php       FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE      TRUE     FALSE                  FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE      FALSE    TRUE      -----------------------------------------------------------------------------------------------------------

User · Answer

Variables have a type and a value     var    test  is a string that contain  test   var2   24 is an integer vhose value is 24    When you use these variables  in PHP   sometimes you don t have the good type  For example  if you do  if   var    1       do something        PHP have to convert   to cast    var to integer  In this case    var    1  is true because any non-empty string is casted to 1   When using      you check that the value AND THE TYPE are equal  so   var     1  is false   This is useful  for example  when you have a function that can return false  on error  and 0  result     if myFunction      false        error on myFunction         This code is wrong as if myFunction   returns 0  it is casted to false and you seem to have an error  The correct code is    if myFunction       false        error on myFunction         because the test is that the return value  is a boolean and is false  and not  can be casted to false

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A picture is worth a thousand words  PHP Double Equals    equality chart   PHP Triple Equals     Equality chart   Source code to create these images  https   github com sentientmachine php equality charts Guru Meditation Those who wish to keep their sanity  read no further because none of this will make any sense  except to say that this is how the insanity-fractal  of PHP was designed   NAN    NAN but NAN    true      will convert left and right operands to numbers if left is a number   So 123     quot 123foo quot   but  quot 123 quot      quot 123foo quot   A hex string in quotes is occasionally a float  and will be surprise cast to float against your will  causing a runtime error      is not transitive because  quot 0 quot    0  and 0     quot  quot  but  quot 0 quot      quot  quot   PHP Variables that have not been declared yet are false  even though PHP has a way to represent undefined variables  that feature is disabled with       quot 6 quot      quot  6 quot    quot 4 2 quot      quot 4 20 quot   and  quot 133 quot      quot 0133 quot  but 133    0133  But  quot 0x10 quot      quot 16 quot  and  quot 1e3 quot      quot 1000 quot  exposing that surprise string conversion to octal will occur both without your instruction or consent  causing a runtime error   False    0   quot  quot      and  quot 0 quot    If you add 1 to number and they are already holding their maximum value  they do not wrap around  instead they are cast to infinity   A fresh class is    to 1   False is the most dangerous value because False is    to most of the other variables  mostly defeating it s purpose    Hope  If you are using PHP  Thou shalt not use the double equals operator because if you use triple equals  the only edge cases to worry about are NAN and numbers so close to their datatype s maximum value  that they are cast to infinity   With double equals  anything can be surprise    to anything or  or can be surprise casted against your will and    to something of which it should obviously be equal  Anywhere you use    in PHP is a bad code smell because of the 85 bugs in it exposed by implicit casting rules that seem designed by millions of programmers programming by brownian motion

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Difference between     equal  and      identical equal  PHP provides two comparison operators to check equality of two values  The main difference between of these two is that      checks if the values of the two operands are equal or not  On the other hand        checks the values as well as the type of operands are equal or not       Equal       Identical equal   Example   gt   lt  php       val1   1234       val2    quot 1234 quot       var dump  val1     val2     output   gt  bool true        It checks only operands value   gt      lt  php       val1   1234       val2    quot 1234 quot       var dump  val1      val2     output   gt  bool false        First it checks type then operands value   gt    if we type cast  val2 to  int  val2 or  string  val1 then it returns true     lt  php           val1   1234           val2    quot 1234 quot           var dump  val1      int  val2     output   gt  bool true            First it checks type then operands value       gt    OR    lt  php           val1   1234           val2    quot 1234 quot           var dump  val1      int  val2     output   gt  bool true            First it checks type then operands value       gt

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The operator    casts between two different types if they are different  while the     operator performs a  typesafe comparison   That means that it will only return true if both operands have the same type and the same value   Examples   1     1  true 1    1  true 1      1   false    1 is an integer   1  is a string 1     1   true     1  gets casted to an integer  which is 1  foo       foo   true    both operands are strings and have the same value  Warning  two instances of the same class with equivalent members do NOT match the     operator  Example    a   new stdClass     a- gt foo    bar    b   clone  a  var dump  a      b      bool false

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There are two differences between    and     in PHP arrays and objects that I think didn t mention here  two arrays with different key sorts  and objects   Two arrays with different key sorts  If you have an array with a key sort and another array with a different key sort  they are strictly different  i e  using       That may cause if you key-sort an array  and try to compare the sorted array with the original one   For instance  consider an empty array  First  we try to push some new indexes to the array without any special sort  A good example would be an array with strings as keys  Now deep into an example      Define an array  arr           Adding unsorted keys  arr  I      we    arr  you      you    arr  he      they     Now  we have a not-sorted-keys array  e g    he  came after  you    Consider the same array  but we sorted its keys alphabetically      Declare array  alphabetArr           Adding alphabetical-sorted keys  alphabetArr  I      we    alphabetArr  he      they    alphabetArr  you      you     Tip  You can sort an array by key using ksort   function   Now you have another array with a different key sort from the first one  So  we re going to compare them    arr     alphabetArr     true  arr      alphabetArr     false   Note  It may be obvious  but comparing two different arrays using strict comparison always results false  However  two arbitrary arrays may be equal using     or not   You would say   This difference is negligible   Then I say it s a difference and should be considered and may happen anytime  As mentioned above  sorting keys in an array is a good example of that   Objects  Keep in mind  two different objects are never strict-equal  These examples would help    stdClass1   new stdClass     stdClass2   new stdClass     clonedStdClass1   clone  stdClass1      Comparing  stdClass1     stdClass2     true  stdClass1      stdClass2     false  stdClass1     clonedStdClass1     true  stdClass1      clonedStdClass1     false   Note  Assigning an object to another variable does not create a copy - rather  it creates a reference to the same memory location as the object  See here   Note  As of PHP7  anonymous classes was added  From the results  there is no difference between new class    and new stdClass   in the tests above

User · Answer

Difference between    and      The difference between the loosely    equal operator and the strict     identical operator is exactly explained in the manual      Comparison Operators    ----------------------------------------------------------------------------------     Example     Name         Result                                                        ---------- ----------- -----------------------------------------------------------      a      b    Equal        TRUE if  a is equal to  b after type juggling                   a      b    Identical    TRUE if  a is equal to  b  and they are of the same type      ----------------------------------------------------------------------------------       Loosely    equal comparison  If you are using the    operator  or any other comparison operator which uses loosely comparison such as      lt  gt  or     you always have to look at the context to see what  where and why something gets converted to understand what is going on   Converting rules   Converting to boolean Converting to integer Converting to float Converting to string Converting to array Converting to object Converting to resource Converting to NULL   Type comparison table  As reference and example you can see the comparison table in the manual      Loose comparisons with      -----------------------------------------------------------------------------------------------------------                TRUE     FALSE      1        0       -1        1        0       -1      NULL     array       php               --------- ------- ------- ------- ------- ------- ------- ------- ------- ------- --------- ------- -------      TRUE       TRUE     FALSE    TRUE     FALSE    TRUE     TRUE     FALSE    TRUE     FALSE    FALSE      TRUE     FALSE       FALSE      FALSE    TRUE     FALSE    TRUE     FALSE    FALSE    TRUE     FALSE    TRUE     TRUE       FALSE    TRUE        1          TRUE     FALSE    TRUE     FALSE    FALSE    TRUE     FALSE    FALSE    FALSE    FALSE      FALSE    FALSE       0          FALSE    TRUE     FALSE    TRUE     FALSE    FALSE    TRUE     FALSE    TRUE     FALSE      TRUE     TRUE        -1         TRUE     FALSE    FALSE    FALSE    TRUE     FALSE    FALSE    TRUE     FALSE    FALSE      FALSE    FALSE        1         TRUE     FALSE    TRUE     FALSE    FALSE    TRUE     FALSE    FALSE    FALSE    FALSE      FALSE    FALSE        0         FALSE    TRUE     FALSE    TRUE     FALSE    FALSE    TRUE     FALSE    FALSE    FALSE      FALSE    FALSE        -1        TRUE     FALSE    FALSE    FALSE    TRUE     FALSE    FALSE    TRUE     FALSE    FALSE      FALSE    FALSE       NULL       FALSE    TRUE     FALSE    TRUE     FALSE    FALSE    FALSE    FALSE    TRUE     TRUE       FALSE    TRUE        array      FALSE    TRUE     FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    TRUE     TRUE       FALSE    FALSE        php       TRUE     FALSE    FALSE    TRUE     FALSE    FALSE    FALSE    FALSE    FALSE    FALSE      TRUE     FALSE                  FALSE    TRUE     FALSE    TRUE     FALSE    FALSE    FALSE    FALSE    TRUE     FALSE      FALSE    TRUE      -----------------------------------------------------------------------------------------------------------     Strict     identical comparison  If you are using the     operator  or any other comparison operator which uses strict comparison such as     or      then you can always be sure that the types won t magically change  because there will be no converting going on  So with strict comparison the type and value have to be the same  not only the value   Type comparison table  As reference and example you can see the comparison table in the manual      Strict comparisons with       -----------------------------------------------------------------------------------------------------------                TRUE     FALSE      1        0       -1        1        0       -1      NULL     array       php               --------- ------- ------- ------- ------- ------- ------- ------- ------- ------- --------- ------- -------      TRUE       TRUE     FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE      FALSE    FALSE       FALSE      FALSE    TRUE     FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE      FALSE    FALSE       1          FALSE    FALSE    TRUE     FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE      FALSE    FALSE       0          FALSE    FALSE    FALSE    TRUE     FALSE    FALSE    FALSE    FALSE    FALSE    FALSE      FALSE    FALSE       -1         FALSE    FALSE    FALSE    FALSE    TRUE     FALSE    FALSE    FALSE    FALSE    FALSE      FALSE    FALSE        1         FALSE    FALSE    FALSE    FALSE    FALSE    TRUE     FALSE    FALSE    FALSE    FALSE      FALSE    FALSE        0         FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    TRUE     FALSE    FALSE    FALSE      FALSE    FALSE        -1        FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    TRUE     FALSE    FALSE      FALSE    FALSE       NULL       FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    TRUE     FALSE      FALSE    FALSE       array      FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    TRUE       FALSE    FALSE        php       FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE      TRUE     FALSE                  FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE      FALSE    TRUE      -----------------------------------------------------------------------------------------------------------

User · Answer

An addition to the other answers concerning object comparison      compares objects using the name of the object and their values  If two objects are of the same type and have the same member values   a     b yields true       compares the internal object id of the objects  Even if the members are equal   a      b if they are not exactly the same object   class TestClassA       public  a     class TestClassB       public  a      a1   new TestClassA     a2   new TestClassA     b   new TestClassB      a1- gt a   10   a2- gt a   10   b- gt a   10    a1     a1   a1     a2      Same members  a1     b       Different classes   a1      a1   a1      a2     Not the same object

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In regards to JavaScript   The     operator works the same as the    operator  but it requires that its operands have not only the same value  but also the same data type   For example  the sample below will display  x and y are equal   but not  x and y are identical    var x   4  var y    4   if  x    y        alert  x and y are equal      if  x     y        alert  x and y are identical

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The operator    casts between two different types if they are different  while the     operator performs a  typesafe comparison   That means that it will only return true if both operands have the same type and the same value   Examples   1     1  true 1    1  true 1      1   false    1 is an integer   1  is a string 1     1   true     1  gets casted to an integer  which is 1  foo       foo   true    both operands are strings and have the same value  Warning  two instances of the same class with equivalent members do NOT match the     operator  Example    a   new stdClass     a- gt foo    bar    b   clone  a  var dump  a      b      bool false

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You would use     to test whether a function or variable is false rather than just equating to false  zero or an empty string     needle    a    haystack    abc    pos   strpos  haystack   needle   if   pos     false        echo  needle     was not found in      haystack    else       echo  needle     was found in      haystack     at location      pos      In this case strpos would return 0 which would equate to false in the test  if   pos    false    or  if    pos    which is not what you want here

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lt  php                 Comparison of two PHP objects                                           Checks for        1  References                                         yes    yes        2  Instances with matching attributes and its values  yes    no        3  Instances with different attributes                yes    no                  There is no need to worry about comparing visibility of property or        method  because it will be the same whenever an object instance is        created  however visibility of an object can be modified during run        time using ReflectionClass          http   php net manual en reflectionproperty setaccessible php            class Foo               public  foobar   1           public function createNewProperty  name   value                         this- gt   name     value                       class Bar                    1  Object handles or references        Is an object a reference to itself or a clone or totally a different object                      true   Name of two objects are same  for example  Foo   and Foo                false  Name of two objects are different  for example  Foo   and Bar                true   ID of two objects are same  for example  1 and 1              false  ID of two objects are different  for example  1 and 2      echo  1  Object handles or references  both    and          lt br   gt          bar   new Foo          New object Foo   created      bar2   new Foo         New object Foo   created      baz   clone  bar       Object Foo   cloned      qux    bar             Object Foo   referenced      norf   new Bar         New object Bar   created     echo  bar       var dump  bar       echo  baz       var dump  baz       echo  qux       var dump  qux       echo  bar2       var dump  bar2       echo  norf       var dump  norf           Clone     true and     false     echo   bar     bar2       var dump  bar     bar2      true      echo   bar      bar2       var dump  bar      bar2      false      echo   bar     baz       var dump  bar     baz      true      echo   bar      baz       var dump  bar      baz      false         Object reference     true and     true     echo   bar     qux       var dump  bar     qux      true      echo   bar      qux       var dump  bar      qux      true         Two different objects     false and     false     echo   bar     norf       var dump  bar     norf      false      echo   bar      norf       var dump  bar      norf      false         2  Instances with matching attributes and its values  only                What happens when objects  even in cloned object  have same           attributes but varying values           foobar value is different     echo  2  Instances with matching attributes  and its values  only      lt br   gt          baz- gt foobar   2      echo   foobar      value is different  lt br   gt        echo   bar- gt foobar        bar- gt foobar     lt br   gt        echo   baz- gt foobar        baz- gt foobar     lt br   gt        echo   bar     baz       var dump  bar     baz      false          foobar s value is the same again      baz- gt foobar   1      echo   foobar      value is the same again  lt br   gt        echo   bar- gt foobar is      bar- gt foobar     lt br   gt        echo   baz- gt foobar is      baz- gt foobar     lt br   gt        echo   bar     baz       var dump  bar     baz      true         Changing values of properties in  qux object will change the property        value of  bar and evaluates true always  because  qux    amp  bar       qux- gt foobar   2      echo   foobar value of both  qux and  bar is 2  because  qux    amp  bar      lt br   gt        echo   qux- gt foobar is      qux- gt foobar     lt br   gt        echo   bar- gt foobar is      bar- gt foobar     lt br   gt        echo   bar     qux       var dump  bar     qux      true         3  Instances with different attributes  only               What happens when objects have different attributes even though           one of the attributes has same value      echo  3  Instances with different attributes  only      lt br   gt            Dynamically create a property with the name in  name and value        in  value for baz object      name    newproperty        value   null       baz- gt createNewProperty  name   value       echo   baz- gt newproperty is      baz- gt   name       var dump  baz         baz- gt foobar   2      echo   foobar      value is same again  lt br   gt        echo   bar- gt foobar is      bar- gt foobar     lt br   gt        echo   baz- gt foobar is      baz- gt foobar     lt br   gt        echo   bar     baz       var dump  bar     baz      false     var dump  bar       var dump  baz     gt

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PHP Double Equals      In most programming languages  the comparison operator      checks  on the one hand  the data type and on the other hand the content of the variable for equality  The standard comparison operator      in PHP behaves differently  This tries to convert both variables into the same data type before the comparison and only then checks whether the content of these variables is the same  The following results are obtained   lt  php     var dump  1    1           true     var dump  1     1          true     var dump  1    2           false     var dump  1     2          false     var dump  1    true        true     var dump  1    false       false   gt   PHP Triple Equals       This operator also checks the datatype of the variable and returns  bool true only if both variables have the same content and the same datatype  The following would therefore be correct   lt  php     var dump  1     1           true     var dump  1      1          false     var dump  1     2           false     var dump  1      2          false     var dump  1     true        false     var dump  1     false       false   gt   Read more in What is the difference between    and     in PHP

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There are two differences between    and     in PHP arrays and objects that I think didn t mention here  two arrays with different key sorts  and objects   Two arrays with different key sorts  If you have an array with a key sort and another array with a different key sort  they are strictly different  i e  using       That may cause if you key-sort an array  and try to compare the sorted array with the original one   For instance  consider an empty array  First  we try to push some new indexes to the array without any special sort  A good example would be an array with strings as keys  Now deep into an example      Define an array  arr           Adding unsorted keys  arr  I      we    arr  you      you    arr  he      they     Now  we have a not-sorted-keys array  e g    he  came after  you    Consider the same array  but we sorted its keys alphabetically      Declare array  alphabetArr           Adding alphabetical-sorted keys  alphabetArr  I      we    alphabetArr  he      they    alphabetArr  you      you     Tip  You can sort an array by key using ksort   function   Now you have another array with a different key sort from the first one  So  we re going to compare them    arr     alphabetArr     true  arr      alphabetArr     false   Note  It may be obvious  but comparing two different arrays using strict comparison always results false  However  two arbitrary arrays may be equal using     or not   You would say   This difference is negligible   Then I say it s a difference and should be considered and may happen anytime  As mentioned above  sorting keys in an array is a good example of that   Objects  Keep in mind  two different objects are never strict-equal  These examples would help    stdClass1   new stdClass     stdClass2   new stdClass     clonedStdClass1   clone  stdClass1      Comparing  stdClass1     stdClass2     true  stdClass1      stdClass2     false  stdClass1     clonedStdClass1     true  stdClass1      clonedStdClass1     false   Note  Assigning an object to another variable does not create a copy - rather  it creates a reference to the same memory location as the object  See here   Note  As of PHP7  anonymous classes was added  From the results  there is no difference between new class    and new stdClass   in the tests above

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Variables have a type and a value     var    test  is a string that contain  test   var2   24 is an integer vhose value is 24    When you use these variables  in PHP   sometimes you don t have the good type  For example  if you do  if   var    1       do something        PHP have to convert   to cast    var to integer  In this case    var    1  is true because any non-empty string is casted to 1   When using      you check that the value AND THE TYPE are equal  so   var     1  is false   This is useful  for example  when you have a function that can return false  on error  and 0  result     if myFunction      false        error on myFunction         This code is wrong as if myFunction   returns 0  it is casted to false and you seem to have an error  The correct code is    if myFunction       false        error on myFunction         because the test is that the return value  is a boolean and is false  and not  can be casted to false

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PHP Double Equals      In most programming languages  the comparison operator      checks  on the one hand  the data type and on the other hand the content of the variable for equality  The standard comparison operator      in PHP behaves differently  This tries to convert both variables into the same data type before the comparison and only then checks whether the content of these variables is the same  The following results are obtained   lt  php     var dump  1    1           true     var dump  1     1          true     var dump  1    2           false     var dump  1     2          false     var dump  1    true        true     var dump  1    false       false   gt   PHP Triple Equals       This operator also checks the datatype of the variable and returns  bool true only if both variables have the same content and the same datatype  The following would therefore be correct   lt  php     var dump  1     1           true     var dump  1      1          false     var dump  1     2           false     var dump  1      2          false     var dump  1     true        false     var dump  1     false       false   gt   Read more in What is the difference between    and     in PHP

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Difference between    and      The difference between the loosely    equal operator and the strict     identical operator is exactly explained in the manual      Comparison Operators    ----------------------------------------------------------------------------------     Example     Name         Result                                                        ---------- ----------- -----------------------------------------------------------      a      b    Equal        TRUE if  a is equal to  b after type juggling                   a      b    Identical    TRUE if  a is equal to  b  and they are of the same type      ----------------------------------------------------------------------------------       Loosely    equal comparison  If you are using the    operator  or any other comparison operator which uses loosely comparison such as      lt  gt  or     you always have to look at the context to see what  where and why something gets converted to understand what is going on   Converting rules   Converting to boolean Converting to integer Converting to float Converting to string Converting to array Converting to object Converting to resource Converting to NULL   Type comparison table  As reference and example you can see the comparison table in the manual      Loose comparisons with      -----------------------------------------------------------------------------------------------------------                TRUE     FALSE      1        0       -1        1        0       -1      NULL     array       php               --------- ------- ------- ------- ------- ------- ------- ------- ------- ------- --------- ------- -------      TRUE       TRUE     FALSE    TRUE     FALSE    TRUE     TRUE     FALSE    TRUE     FALSE    FALSE      TRUE     FALSE       FALSE      FALSE    TRUE     FALSE    TRUE     FALSE    FALSE    TRUE     FALSE    TRUE     TRUE       FALSE    TRUE        1          TRUE     FALSE    TRUE     FALSE    FALSE    TRUE     FALSE    FALSE    FALSE    FALSE      FALSE    FALSE       0          FALSE    TRUE     FALSE    TRUE     FALSE    FALSE    TRUE     FALSE    TRUE     FALSE      TRUE     TRUE        -1         TRUE     FALSE    FALSE    FALSE    TRUE     FALSE    FALSE    TRUE     FALSE    FALSE      FALSE    FALSE        1         TRUE     FALSE    TRUE     FALSE    FALSE    TRUE     FALSE    FALSE    FALSE    FALSE      FALSE    FALSE        0         FALSE    TRUE     FALSE    TRUE     FALSE    FALSE    TRUE     FALSE    FALSE    FALSE      FALSE    FALSE        -1        TRUE     FALSE    FALSE    FALSE    TRUE     FALSE    FALSE    TRUE     FALSE    FALSE      FALSE    FALSE       NULL       FALSE    TRUE     FALSE    TRUE     FALSE    FALSE    FALSE    FALSE    TRUE     TRUE       FALSE    TRUE        array      FALSE    TRUE     FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    TRUE     TRUE       FALSE    FALSE        php       TRUE     FALSE    FALSE    TRUE     FALSE    FALSE    FALSE    FALSE    FALSE    FALSE      TRUE     FALSE                  FALSE    TRUE     FALSE    TRUE     FALSE    FALSE    FALSE    FALSE    TRUE     FALSE      FALSE    TRUE      -----------------------------------------------------------------------------------------------------------     Strict     identical comparison  If you are using the     operator  or any other comparison operator which uses strict comparison such as     or      then you can always be sure that the types won t magically change  because there will be no converting going on  So with strict comparison the type and value have to be the same  not only the value   Type comparison table  As reference and example you can see the comparison table in the manual      Strict comparisons with       -----------------------------------------------------------------------------------------------------------                TRUE     FALSE      1        0       -1        1        0       -1      NULL     array       php               --------- ------- ------- ------- ------- ------- ------- ------- ------- ------- --------- ------- -------      TRUE       TRUE     FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE      FALSE    FALSE       FALSE      FALSE    TRUE     FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE      FALSE    FALSE       1          FALSE    FALSE    TRUE     FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE      FALSE    FALSE       0          FALSE    FALSE    FALSE    TRUE     FALSE    FALSE    FALSE    FALSE    FALSE    FALSE      FALSE    FALSE       -1         FALSE    FALSE    FALSE    FALSE    TRUE     FALSE    FALSE    FALSE    FALSE    FALSE      FALSE    FALSE        1         FALSE    FALSE    FALSE    FALSE    FALSE    TRUE     FALSE    FALSE    FALSE    FALSE      FALSE    FALSE        0         FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    TRUE     FALSE    FALSE    FALSE      FALSE    FALSE        -1        FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    TRUE     FALSE    FALSE      FALSE    FALSE       NULL       FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    TRUE     FALSE      FALSE    FALSE       array      FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    TRUE       FALSE    FALSE        php       FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE      TRUE     FALSE                  FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE      FALSE    TRUE      -----------------------------------------------------------------------------------------------------------

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Variables have a type and a value     var    test  is a string that contain  test   var2   24 is an integer vhose value is 24    When you use these variables  in PHP   sometimes you don t have the good type  For example  if you do  if   var    1       do something        PHP have to convert   to cast    var to integer  In this case    var    1  is true because any non-empty string is casted to 1   When using      you check that the value AND THE TYPE are equal  so   var     1  is false   This is useful  for example  when you have a function that can return false  on error  and 0  result     if myFunction      false        error on myFunction         This code is wrong as if myFunction   returns 0  it is casted to false and you seem to have an error  The correct code is    if myFunction       false        error on myFunction         because the test is that the return value  is a boolean and is false  and not  can be casted to false

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You would use     to test whether a function or variable is false rather than just equating to false  zero or an empty string     needle    a    haystack    abc    pos   strpos  haystack   needle   if   pos     false        echo  needle     was not found in      haystack    else       echo  needle     was found in      haystack     at location      pos      In this case strpos would return 0 which would equate to false in the test  if   pos    false    or  if    pos    which is not what you want here

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An addition to the other answers concerning object comparison      compares objects using the name of the object and their values  If two objects are of the same type and have the same member values   a     b yields true       compares the internal object id of the objects  Even if the members are equal   a      b if they are not exactly the same object   class TestClassA       public  a     class TestClassB       public  a      a1   new TestClassA     a2   new TestClassA     b   new TestClassB      a1- gt a   10   a2- gt a   10   b- gt a   10    a1     a1   a1     a2      Same members  a1     b       Different classes   a1      a1   a1      a2     Not the same object

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Difference between     equal  and      identical equal  PHP provides two comparison operators to check equality of two values  The main difference between of these two is that      checks if the values of the two operands are equal or not  On the other hand        checks the values as well as the type of operands are equal or not       Equal       Identical equal   Example   gt   lt  php       val1   1234       val2    quot 1234 quot       var dump  val1     val2     output   gt  bool true        It checks only operands value   gt      lt  php       val1   1234       val2    quot 1234 quot       var dump  val1      val2     output   gt  bool false        First it checks type then operands value   gt    if we type cast  val2 to  int  val2 or  string  val1 then it returns true     lt  php           val1   1234           val2    quot 1234 quot           var dump  val1      int  val2     output   gt  bool true            First it checks type then operands value       gt    OR    lt  php           val1   1234           val2    quot 1234 quot           var dump  val1      int  val2     output   gt  bool true            First it checks type then operands value       gt

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It s all about data types  Take a BOOL  true or false  for example   true also equals 1 and false also equals 0  The    does not care about the data types when comparing  So if you had a variable that is 1  which could also be true     var 1   And then compare with the      if   var    true        echo var is true       But  var does not actually equal true  does it  It has the int value of 1 instead  which in turn  is equal to true   With      the data types are checked to make sure the two variables objects whatever are using the same type   So if I did  if   var     true        echo  var is true       that condition would not be true  as  var     true it only    true  if you know what I mean    Why would you need this   Simple - let s take a look at one of PHP s functions  array search     The array search   function simply searches for a value in an array  and returns the key of the element the value was found in  If the value could not be found in the array  it returns false  But  what if you did an array search   on a value that was stored in the first element of the array  which would have the array key of 0     the array search   function would return 0   which is equal to false    So if you did    arr   array  name    if  array search  name    arr     false           This would return 0  the key of the element the val was found        in   but because we re using     we ll think the function        actually returned false   when it didn t      So  do you see how this could be an issue now   Most people don t use    false when checking if a function returns false  Instead  they use the    But actually  this is exactly the same as using   false  so if you did    arr   array  name    if   array search  name    arr      This is the same as doing  array search  name    arr     false    So for things like that  you would use the     instead  so that the data type is checked

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You would use     to test whether a function or variable is false rather than just equating to false  zero or an empty string     needle    a    haystack    abc    pos   strpos  haystack   needle   if   pos     false        echo  needle     was not found in      haystack    else       echo  needle     was found in      haystack     at location      pos      In this case strpos would return 0 which would equate to false in the test  if   pos    false    or  if    pos    which is not what you want here

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It s all about data types  Take a BOOL  true or false  for example   true also equals 1 and false also equals 0  The    does not care about the data types when comparing  So if you had a variable that is 1  which could also be true     var 1   And then compare with the      if   var    true        echo var is true       But  var does not actually equal true  does it  It has the int value of 1 instead  which in turn  is equal to true   With      the data types are checked to make sure the two variables objects whatever are using the same type   So if I did  if   var     true        echo  var is true       that condition would not be true  as  var     true it only    true  if you know what I mean    Why would you need this   Simple - let s take a look at one of PHP s functions  array search     The array search   function simply searches for a value in an array  and returns the key of the element the value was found in  If the value could not be found in the array  it returns false  But  what if you did an array search   on a value that was stored in the first element of the array  which would have the array key of 0     the array search   function would return 0   which is equal to false    So if you did    arr   array  name    if  array search  name    arr     false           This would return 0  the key of the element the val was found        in   but because we re using     we ll think the function        actually returned false   when it didn t      So  do you see how this could be an issue now   Most people don t use    false when checking if a function returns false  Instead  they use the    But actually  this is exactly the same as using   false  so if you did    arr   array  name    if   array search  name    arr      This is the same as doing  array search  name    arr     false    So for things like that  you would use the     instead  so that the data type is checked

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A picture is worth a thousand words  PHP Double Equals    equality chart   PHP Triple Equals     Equality chart   Source code to create these images  https   github com sentientmachine php equality charts Guru Meditation Those who wish to keep their sanity  read no further because none of this will make any sense  except to say that this is how the insanity-fractal  of PHP was designed   NAN    NAN but NAN    true      will convert left and right operands to numbers if left is a number   So 123     quot 123foo quot   but  quot 123 quot      quot 123foo quot   A hex string in quotes is occasionally a float  and will be surprise cast to float against your will  causing a runtime error      is not transitive because  quot 0 quot    0  and 0     quot  quot  but  quot 0 quot      quot  quot   PHP Variables that have not been declared yet are false  even though PHP has a way to represent undefined variables  that feature is disabled with       quot 6 quot      quot  6 quot    quot 4 2 quot      quot 4 20 quot   and  quot 133 quot      quot 0133 quot  but 133    0133  But  quot 0x10 quot      quot 16 quot  and  quot 1e3 quot      quot 1000 quot  exposing that surprise string conversion to octal will occur both without your instruction or consent  causing a runtime error   False    0   quot  quot      and  quot 0 quot    If you add 1 to number and they are already holding their maximum value  they do not wrap around  instead they are cast to infinity   A fresh class is    to 1   False is the most dangerous value because False is    to most of the other variables  mostly defeating it s purpose    Hope  If you are using PHP  Thou shalt not use the double equals operator because if you use triple equals  the only edge cases to worry about are NAN and numbers so close to their datatype s maximum value  that they are cast to infinity   With double equals  anything can be surprise    to anything or  or can be surprise casted against your will and    to something of which it should obviously be equal  Anywhere you use    in PHP is a bad code smell because of the 85 bugs in it exposed by implicit casting rules that seem designed by millions of programmers programming by brownian motion

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Difference between    and      The difference between the loosely    equal operator and the strict     identical operator is exactly explained in the manual      Comparison Operators    ----------------------------------------------------------------------------------     Example     Name         Result                                                        ---------- ----------- -----------------------------------------------------------      a      b    Equal        TRUE if  a is equal to  b after type juggling                   a      b    Identical    TRUE if  a is equal to  b  and they are of the same type      ----------------------------------------------------------------------------------       Loosely    equal comparison  If you are using the    operator  or any other comparison operator which uses loosely comparison such as      lt  gt  or     you always have to look at the context to see what  where and why something gets converted to understand what is going on   Converting rules   Converting to boolean Converting to integer Converting to float Converting to string Converting to array Converting to object Converting to resource Converting to NULL   Type comparison table  As reference and example you can see the comparison table in the manual      Loose comparisons with      -----------------------------------------------------------------------------------------------------------                TRUE     FALSE      1        0       -1        1        0       -1      NULL     array       php               --------- ------- ------- ------- ------- ------- ------- ------- ------- ------- --------- ------- -------      TRUE       TRUE     FALSE    TRUE     FALSE    TRUE     TRUE     FALSE    TRUE     FALSE    FALSE      TRUE     FALSE       FALSE      FALSE    TRUE     FALSE    TRUE     FALSE    FALSE    TRUE     FALSE    TRUE     TRUE       FALSE    TRUE        1          TRUE     FALSE    TRUE     FALSE    FALSE    TRUE     FALSE    FALSE    FALSE    FALSE      FALSE    FALSE       0          FALSE    TRUE     FALSE    TRUE     FALSE    FALSE    TRUE     FALSE    TRUE     FALSE      TRUE     TRUE        -1         TRUE     FALSE    FALSE    FALSE    TRUE     FALSE    FALSE    TRUE     FALSE    FALSE      FALSE    FALSE        1         TRUE     FALSE    TRUE     FALSE    FALSE    TRUE     FALSE    FALSE    FALSE    FALSE      FALSE    FALSE        0         FALSE    TRUE     FALSE    TRUE     FALSE    FALSE    TRUE     FALSE    FALSE    FALSE      FALSE    FALSE        -1        TRUE     FALSE    FALSE    FALSE    TRUE     FALSE    FALSE    TRUE     FALSE    FALSE      FALSE    FALSE       NULL       FALSE    TRUE     FALSE    TRUE     FALSE    FALSE    FALSE    FALSE    TRUE     TRUE       FALSE    TRUE        array      FALSE    TRUE     FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    TRUE     TRUE       FALSE    FALSE        php       TRUE     FALSE    FALSE    TRUE     FALSE    FALSE    FALSE    FALSE    FALSE    FALSE      TRUE     FALSE                  FALSE    TRUE     FALSE    TRUE     FALSE    FALSE    FALSE    FALSE    TRUE     FALSE      FALSE    TRUE      -----------------------------------------------------------------------------------------------------------     Strict     identical comparison  If you are using the     operator  or any other comparison operator which uses strict comparison such as     or      then you can always be sure that the types won t magically change  because there will be no converting going on  So with strict comparison the type and value have to be the same  not only the value   Type comparison table  As reference and example you can see the comparison table in the manual      Strict comparisons with       -----------------------------------------------------------------------------------------------------------                TRUE     FALSE      1        0       -1        1        0       -1      NULL     array       php               --------- ------- ------- ------- ------- ------- ------- ------- ------- ------- --------- ------- -------      TRUE       TRUE     FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE      FALSE    FALSE       FALSE      FALSE    TRUE     FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE      FALSE    FALSE       1          FALSE    FALSE    TRUE     FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE      FALSE    FALSE       0          FALSE    FALSE    FALSE    TRUE     FALSE    FALSE    FALSE    FALSE    FALSE    FALSE      FALSE    FALSE       -1         FALSE    FALSE    FALSE    FALSE    TRUE     FALSE    FALSE    FALSE    FALSE    FALSE      FALSE    FALSE        1         FALSE    FALSE    FALSE    FALSE    FALSE    TRUE     FALSE    FALSE    FALSE    FALSE      FALSE    FALSE        0         FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    TRUE     FALSE    FALSE    FALSE      FALSE    FALSE        -1        FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    TRUE     FALSE    FALSE      FALSE    FALSE       NULL       FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    TRUE     FALSE      FALSE    FALSE       array      FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    TRUE       FALSE    FALSE        php       FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE      TRUE     FALSE                  FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE    FALSE      FALSE    TRUE      -----------------------------------------------------------------------------------------------------------

User · Answer

Variables have a type and a value     var    test  is a string that contain  test   var2   24 is an integer vhose value is 24    When you use these variables  in PHP   sometimes you don t have the good type  For example  if you do  if   var    1       do something        PHP have to convert   to cast    var to integer  In this case    var    1  is true because any non-empty string is casted to 1   When using      you check that the value AND THE TYPE are equal  so   var     1  is false   This is useful  for example  when you have a function that can return false  on error  and 0  result     if myFunction      false        error on myFunction         This code is wrong as if myFunction   returns 0  it is casted to false and you seem to have an error  The correct code is    if myFunction       false        error on myFunction         because the test is that the return value  is a boolean and is false  and not  can be casted to false

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All of the answers so far ignore a dangerous problem with      It has been noted in passing  but not stressed  that integer and double are different types  so the following code    n   1000   d    n   0 0e0  echo   lt br  gt        n      d   equal    not equal     echo   lt br  gt        n      d   equal    not equal       gives    equal  not equal   Note that this is NOT a case of a  rounding error   The two numbers are exactly equal down to the last bit  but they have different types   This is a nasty problem because a program using     can run happily for years if all of the numbers are small enough  where  small enough  depends on the hardware and OS you are running on   However  if by chance  an integer happens to be large enough to be converted to a double  its type is changed  forever  even though a subsequent operation  or many operations  might bring it back to a small integer in value  And  it gets worse  It can spread - double-ness infection can be passed along to anything it touches  one calculation at a time    In the real world  this is likely to be a problem in programs that handle dates beyond the year 2038  for example  At this time  UNIX timestamps  number of seconds since 1970-01-01 00 00 00 UTC  will require more than 32-bits  so their representation will  magically  switch to double on some systems  Therefore  if you calculate the difference between two times you might end up with a couple of seconds  but as a double  rather than the integer result that occurs in the year 2017   I think this is much worse than conversions between strings and numbers because it is subtle  I find it easy to keep track of what is a string and what is a number  but keeping track of the number of bits in a number is beyond me   So  in the above answers there are some nice tables  but no distinction between 1  as an integer  and 1  subtle double  and 1 0  obvious double   Also  advice that you should always use     and never    is not great because     will sometimes fail where    works properly  Also  JavaScript is not equivalent in this regard because it has only one number type  internally it may have different bit-wise representations  but it does not cause problems for        My advice - use neither  You need to write your own comparison function to really fix this mess

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lt  php                 Comparison of two PHP objects                                           Checks for        1  References                                         yes    yes        2  Instances with matching attributes and its values  yes    no        3  Instances with different attributes                yes    no                  There is no need to worry about comparing visibility of property or        method  because it will be the same whenever an object instance is        created  however visibility of an object can be modified during run        time using ReflectionClass          http   php net manual en reflectionproperty setaccessible php            class Foo               public  foobar   1           public function createNewProperty  name   value                         this- gt   name     value                       class Bar                    1  Object handles or references        Is an object a reference to itself or a clone or totally a different object                      true   Name of two objects are same  for example  Foo   and Foo                false  Name of two objects are different  for example  Foo   and Bar                true   ID of two objects are same  for example  1 and 1              false  ID of two objects are different  for example  1 and 2      echo  1  Object handles or references  both    and          lt br   gt          bar   new Foo          New object Foo   created      bar2   new Foo         New object Foo   created      baz   clone  bar       Object Foo   cloned      qux    bar             Object Foo   referenced      norf   new Bar         New object Bar   created     echo  bar       var dump  bar       echo  baz       var dump  baz       echo  qux       var dump  qux       echo  bar2       var dump  bar2       echo  norf       var dump  norf           Clone     true and     false     echo   bar     bar2       var dump  bar     bar2      true      echo   bar      bar2       var dump  bar      bar2      false      echo   bar     baz       var dump  bar     baz      true      echo   bar      baz       var dump  bar      baz      false         Object reference     true and     true     echo   bar     qux       var dump  bar     qux      true      echo   bar      qux       var dump  bar      qux      true         Two different objects     false and     false     echo   bar     norf       var dump  bar     norf      false      echo   bar      norf       var dump  bar      norf      false         2  Instances with matching attributes and its values  only                What happens when objects  even in cloned object  have same           attributes but varying values           foobar value is different     echo  2  Instances with matching attributes  and its values  only      lt br   gt          baz- gt foobar   2      echo   foobar      value is different  lt br   gt        echo   bar- gt foobar        bar- gt foobar     lt br   gt        echo   baz- gt foobar        baz- gt foobar     lt br   gt        echo   bar     baz       var dump  bar     baz      false          foobar s value is the same again      baz- gt foobar   1      echo   foobar      value is the same again  lt br   gt        echo   bar- gt foobar is      bar- gt foobar     lt br   gt        echo   baz- gt foobar is      baz- gt foobar     lt br   gt        echo   bar     baz       var dump  bar     baz      true         Changing values of properties in  qux object will change the property        value of  bar and evaluates true always  because  qux    amp  bar       qux- gt foobar   2      echo   foobar value of both  qux and  bar is 2  because  qux    amp  bar      lt br   gt        echo   qux- gt foobar is      qux- gt foobar     lt br   gt        echo   bar- gt foobar is      bar- gt foobar     lt br   gt        echo   bar     qux       var dump  bar     qux      true         3  Instances with different attributes  only               What happens when objects have different attributes even though           one of the attributes has same value      echo  3  Instances with different attributes  only      lt br   gt            Dynamically create a property with the name in  name and value        in  value for baz object      name    newproperty        value   null       baz- gt createNewProperty  name   value       echo   baz- gt newproperty is      baz- gt   name       var dump  baz         baz- gt foobar   2      echo   foobar      value is same again  lt br   gt        echo   bar- gt foobar is      bar- gt foobar     lt br   gt        echo   baz- gt foobar is      baz- gt foobar     lt br   gt        echo   bar     baz       var dump  bar     baz      false     var dump  bar       var dump  baz     gt

User · Answer

In regards to JavaScript   The     operator works the same as the    operator  but it requires that its operands have not only the same value  but also the same data type   For example  the sample below will display  x and y are equal   but not  x and y are identical    var x   4  var y    4   if  x    y        alert  x and y are equal      if  x     y        alert  x and y are identical

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All of the answers so far ignore a dangerous problem with      It has been noted in passing  but not stressed  that integer and double are different types  so the following code    n   1000   d    n   0 0e0  echo   lt br  gt        n      d   equal    not equal     echo   lt br  gt        n      d   equal    not equal       gives    equal  not equal   Note that this is NOT a case of a  rounding error   The two numbers are exactly equal down to the last bit  but they have different types   This is a nasty problem because a program using     can run happily for years if all of the numbers are small enough  where  small enough  depends on the hardware and OS you are running on   However  if by chance  an integer happens to be large enough to be converted to a double  its type is changed  forever  even though a subsequent operation  or many operations  might bring it back to a small integer in value  And  it gets worse  It can spread - double-ness infection can be passed along to anything it touches  one calculation at a time    In the real world  this is likely to be a problem in programs that handle dates beyond the year 2038  for example  At this time  UNIX timestamps  number of seconds since 1970-01-01 00 00 00 UTC  will require more than 32-bits  so their representation will  magically  switch to double on some systems  Therefore  if you calculate the difference between two times you might end up with a couple of seconds  but as a double  rather than the integer result that occurs in the year 2017   I think this is much worse than conversions between strings and numbers because it is subtle  I find it easy to keep track of what is a string and what is a number  but keeping track of the number of bits in a number is beyond me   So  in the above answers there are some nice tables  but no distinction between 1  as an integer  and 1  subtle double  and 1 0  obvious double   Also  advice that you should always use     and never    is not great because     will sometimes fail where    works properly  Also  JavaScript is not equivalent in this regard because it has only one number type  internally it may have different bit-wise representations  but it does not cause problems for        My advice - use neither  You need to write your own comparison function to really fix this mess

User · Answer

In regards to JavaScript   The     operator works the same as the    operator  but it requires that its operands have not only the same value  but also the same data type   For example  the sample below will display  x and y are equal   but not  x and y are identical    var x   4  var y    4   if  x    y        alert  x and y are equal      if  x     y        alert  x and y are identical

User · Answer

In regards to JavaScript   The     operator works the same as the    operator  but it requires that its operands have not only the same value  but also the same data type   For example  the sample below will display  x and y are equal   but not  x and y are identical    var x   4  var y    4   if  x    y        alert  x and y are equal      if  x     y        alert  x and y are identical

[php] How do the PHP equality (== double equals) and identity (=== triple equals) comparison operators differ?

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