Are PHP Variables passed by value or by reference

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Are PHP variables passed by value or by reference

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Use this for functions when you wish to simply alter the original variable and return it again to the same variable name with its new value assigned   function add  amp  var      The  amp amp  is before the argument  var     var       a   1   b   10  add  a   echo  a is  a    add  b   echo   a is  a  and b is  b      Note   a and  b are NOT referenced

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You can pass a variable to a function by reference  This function will be able to modify the original variable   You can define the passage by reference in the function definition    lt  php function changeValue  amp  var         var        result 5  changeValue  result    echo  result      result is 6 here   gt

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You can do it either way  Put an   amp   symbol in front and the variable you are passing becomes one and the same as its origin i e  you can pass by reference  rather than make a copy of it  so      fred   5       larry    amp   fred       larry   8      echo  fred   this will output 8  as larry and fred are now the same reference

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It s by value according to the PHP Documentation      By default  function arguments are passed by value  so that if the value of the argument within the function is changed  it does not get changed outside of the function   To allow a function to modify its arguments  they must be passed by reference       To have an argument to a function always passed by reference  prepend an ampersand   amp   to the argument name in the function definition     lt  php function add some extra  amp  string         string     and something extra        str    This is a string     add some extra  str   echo  str        outputs  This is a string  and something extra     gt

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PHP variables are assigned by value  passed to functions by value and when containing representing objects are passed by reference  You can force variables to pass by reference using an   amp    Assigned by value reference example   var1    quot test quot    var2    var1   var2    quot new test quot    var3    amp  var2   var3    quot final test quot    print   quot var1   var1  var2   var2  var3   var3    output   var1  test  var2  final test  var3  final test  Passed by value reference example   var1    quot foo quot    var2    quot bar quot    changeThem  var1   var2    print  quot var1   var1  var2   var2 quot    function changeThem  var1   amp  var2        var1    quot FOO quot        var2    quot BAR quot      output   var1  foo  var2 BAR  Object variables passed by reference example  class Foo      public  var1       function   construct             this- gt var1    quot foo quot              public function printFoo            print  this- gt var1             foo   new Foo     changeFoo  foo     foo- gt printFoo     function changeFoo  foo        foo- gt var1    quot FOO quot      output   FOO   The last example could be better probably

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Depends on the version  4 is by value  5 is by reference

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It seems a lot of people get confused by the way objects are passed to functions and what passing by reference means  Object are still passed by value  it s just the value that is passed in PHP5 is a reference handle  As proof   lt  php class Holder       private  value       public function   construct  value             this- gt value    value             public function getValue             return  this- gt value           function swap  x   y         tmp    x       x    y       y    tmp      a   new Holder  a     b   new Holder  b    swap  a   b    echo  a- gt getValue      quot    quot     b- gt getValue      quot  n quot    Outputs  a  b  To pass by reference means we can modify the variables that are seen by the caller  which clearly the code above does not do  We need to change the swap function to   lt  php function swap  amp  x   amp  y         tmp    x       x    y       y    tmp      a   new Holder  a     b   new Holder  b    swap  a   b    echo  a- gt getValue      quot    quot     b- gt getValue      quot  n quot    Outputs  b  a  in order to pass by reference

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In PHP  by default  objects are passed as reference to a new object  See this example  class X     var  abc   10      class Y      var  abc   20     function changeValue  obj          obj- gt abc   30          x   new X     y   new Y     echo  x- gt abc    outputs 10  y- gt changeValue  x   echo  x- gt abc    outputs 30  Now see this  class X     var  abc   10      class Y      var  abc   20     function changeValue  obj           obj   new Y            x   new X     y   new Y     echo  x- gt abc    outputs 10  y- gt changeValue  x   echo  x- gt abc    outputs 10 not 20 same as java does   Now see this  class X     var  abc   10      class Y      var  abc   20     function changeValue  amp  obj           obj   new Y            x   new X     y   new Y     echo  x- gt abc    outputs 10  y- gt changeValue  x   echo  x- gt abc    outputs 20 not possible in java   I hope you can understand this

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http   www php net manual en migration5 oop php     In PHP 5 there is a new Object Model  PHP s handling of objects has been completely rewritten  allowing for better performance and more features  In previous versions of PHP  objects were handled like primitive types  for instance integers and strings   The drawback of this method was that semantically the whole object was copied when a variable was assigned  or passed as a parameter to a method  In the new approach  objects are referenced by handle  and not by value  one can think of a handle as an object s identifier

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class Holder       private  value       public function   construct   value                  this- gt value    value             public function getValue                 return  this- gt value             public function setValue   value                 return  this- gt value    value           class Swap              public function SwapObjects  Holder  x  Holder  y                  tmp    x            x    y            y    tmp             public function SwapValues  Holder  x  Holder  y                  tmp    x- gt getValue              x- gt setValue  y- gt getValue               y- gt setValue  tmp              a1   new Holder  a      b1   new Holder  b        a2   new Holder  a      b2   new Holder  b      Swap  SwapValues  a1   b1    Swap  SwapObjects  a2   b2      echo  SwapValues       a2- gt getValue             b2- gt getValue       lt br gt     echo  SwapObjects       a1- gt getValue             b1- gt getValue       lt br gt      Attributes are still modifiable when not passed by reference so beware   Output   SwapObjects  b  a SwapValues  a  b

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For anyone who comes across this in the future  I want to share this gem from the PHP docs  posted by an anonymous user      There seems to be some confusion here  The distinction between pointers and references is not particularly helpful    The behavior in some of the  comprehensive  examples already posted can be explained in simpler unifying terms  Hayley s code  for example  is doing EXACTLY what you should expect it should   Using    5 3       First principle    A pointer stores a memory address to access an object  Any time an object is assigned  a pointer is generated   I haven t delved TOO deeply into the Zend engine yet  but as far as I can see  this applies       2nd principle  and source of the most confusion    Passing a variable to a function is done by default as a value pass  ie  you are working with a copy   But objects are passed by reference   A common misconception both here and in the Java world  I never said a copy OF WHAT  The default passing is done by value  Always  WHAT is being copied and passed  however  is the pointer  When using the  -    you will of course be accessing the same internals as the original variable in the caller function  Just using     will only play with copies       3rd principle      amp   automatically and permanently sets another variable name pointer to the same memory address as something else until you decouple them  It is correct to use the term  alias  here  Think of it as joining two pointers at the hip until forcibly separated with  unset     This functionality exists both in the same scope and when an argument is passed to a function  Often the passed argument is called a  reference   due to certain distinctions between  passing by value  and  passing by reference  that were clearer in C and C         Just remember  pointers to objects  not objects themselves  are passed to functions  These pointers are COPIES of the original unless you use   amp   in your parameter list to actually pass the originals  Only when you dig into the internals of an object will the originals change    And here s the example they provide    lt  php    The two are meant to be the same  a    Clark Kent     a  Clark Kent  b    amp  a    The two will now share the same fate    b  Superman       a   Superman  too  echo  a  echo  a  Clark Kent       b   Clark Kent  too  unset  b       b divorced from  a  b  Bizarro   echo  a      a   Clark Kent  still  since  b is a free agent pointer now     The two are NOT meant to be the same   c  King    d  Pretender to the Throne   echo  c   n       c   King  echo  d   n       d   Pretender to the Throne  swapByValue  c   d   echo  c   n       c   King  echo  d   n       d   Pretender to the Throne  swapByRef  c   d   echo  c   n       c   Pretender to the Throne  echo  d   n       d   King   function swapByValue  x   y    temp  x   x  y   y  temp    All this beautiful work will disappear   because it was done on COPIES of pointers    The originals pointers still point as they did     function swapByRef  amp  x   amp  y    temp  x   x  y   y  temp    Note the parameter list  now we switched  em REAL good       gt    I wrote an extensive  detailed blog post on this subject for JavaScript  but I believe it applies equally well to PHP  C    and any other language where people seem to be confused about pass by value vs  pass by reference   Clearly  PHP  like C    is a language that does support pass by reference  By default  objects are passed by value  When working with variables that store objects  it helps to see those variables as pointers  because that is fundamentally what they are  at the assembly level   If you pass a pointer by value  you can still  trace  the pointer and modify the properties of the object being pointed to  What you cannot do is have it point to a different object  Only if you explicitly declare a parameter as being passed by reference will you be able to do that

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Variables containing primitive types are passed by value in PHP5  Variables containing objects are passed by reference  There s quite an interesting article from Linux Journal from 2006 which mentions this and other OO differences between 4 and 5   http   www linuxjournal com article 9170

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Actually both methods are valid but it depends upon your requirement  Passing values by reference often makes your script slow  So it s better to pass variables by value considering time of execution  Also the code flow is more consistent when you pass variables by value

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Objects are passed by reference in PHP 5 and by value in PHP 4  Variables are passed by value by default   Read here  http   www webeks net programming php ampersand-operator-used-for-assigning-reference html

[php] Are PHP Variables passed by value or by reference?

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