what's the meaning of the result of var_dump (object)?

Question

var_dump(object) returns: object()#1
I really want to know what's the difference between object()#1, object()#2, and object()#3.
Any help is appreciated.

Answer 1

From a user's point of view, the number is an arbitrary ID which can be used to see if two variables point to the same object; it is unique across all objects in a program, regardless of class and scope.

It can be retrieved directly using the spl_object_id function. For instance:

class Test {}

$test1 = new Test;
$test1_id = spl_object_id( $test1 );
$test2 = new Test;
$test2_id = spl_object_id( $test2 );

var_dump( $test1 );
var_dump( $test2 );
var_dump( $test1_id );
var_dump( $test2_id );

Will output something like this:

object(Test)#1 (0) {
}
object(Test)#2 (0) {
}
int(1)
int(2)

The actual number should not be relied on as having any meaning, but in practice each object created is assigned a sequential ID, resetting at the start of each execution (HTTP request, or script invocation).

To give a very quick technical explanation, inside the definition of var_dump, this is the line that produces the output:

php_printf("%sobject(%s)#%d (%d) {\n", COMMON, ZSTR_VAL(class_name), Z_OBJ_HANDLE_P(struc), myht ? zend_array_count(myht) : 0);

The Z_OBJ_HANDLE_P(struc) macro expands roughly to (*struc).value.obj->handle - it is looking up the handle member from the C struct representing the object. That is initialised in a function called zend_objects_store_put which has this line:

handle = EG(objects_store).top++;

EG stands for "Execution Global", so this ultimately says "increment a counter in a per-execution store, and use that as the handle for the new object".

Which is why my example above, run without any other code, will give IDs of 1 and 2: the first two items to be added to the store during that execution.

Answer 2

For objects with identical information (same class, same properties) it allows to determine whether they are the same instance. For example:

$a = new DateTime();
$b = $a; // Link to same instance
$c = clone $a; // Create a new copy
var_dump($a, $b, $c);

object(DateTime)#1 (3) {
  ["date"]=>
  string(26) "2020-08-15 19:23:39.016441"
  ["timezone_type"]=>
  int(3)
  ["timezone"]=>
  string(16) "Europe/Amsterdam"
}
object(DateTime)#1 (3) {
  ["date"]=>
  string(26) "2020-08-15 19:23:39.016441"
  ["timezone_type"]=>
  int(3)
  ["timezone"]=>
  string(16) "Europe/Amsterdam"
}
object(DateTime)#2 (3) {
  ["date"]=>
  string(26) "2020-08-15 19:23:39.016441"
  ["timezone_type"]=>
  int(3)
  ["timezone"]=>
  string(16) "Europe/Amsterdam"
}

Answer 3

Simply put:

• #1 means first object to be declared
• #2: second object to be declared
• #3: etc.

The behavior is slightly different if one object has been reinitialized (re-assigned) in the course of the script.

Example

class MyClass
{
}

$obj1 = new MyClass;
$obj2 = new stdClass;
$obj3 = new MyClass;
$obj3 = (object) [];

var_dump($obj3);
var_dump($obj1);
var_dump($obj4);
var_dump($obj2);

Result:

object(MyClass)#3 (0) {
}
object(MyClass)#1 (0) {
}
object(stdClass)#4 (0) {
}
object(stdClass)#2 (0) {
}

As you can see, no matter the order of the var_dump, #number tells the order in which the object where instanciated.

Answer 4

var_dump dumps information about a variable. This function displays structured information about one or more expressions that include its type and value. Arrays and objects are explored recursively with values indented to show structure.

object()#1 ,object()#2,and object()#3 are the different object values inside a nested object which have been evaluated and given an id by var_dump

Read more here https://www.php.net/manual/en/function.var-dump.php

Edit 2

It seems Object()#number is the order in which it finds some key/value pair inside a nested object. If an object doesn't contain any key/value pair and just contains another object (with key/value pair), that inner object is evaluated first and the #number is given accordingly. The outer object is evaluated last.

Also, the Object()#number is carried over if a different object is evaluated. The Object()#number starts from where it ended in the first object

Here is an example. This code will decode the JSON and dump the output of the object

<?php
$a= '{
    "glossary": {
        "title": "example glossary",
        "GlossDiv": {
            "title": "S",
            "GlossList": {
                "GlossEntry": {
                    "ID": "SGML",
                    "SortAs": "SGML",
                    "GlossTerm": "Standard Generalized Markup Language",
                    "Acronym": "SGML",
                    "Abbrev": "ISO 8879:1986",
                    "GlossDef": {
                        "para": "A meta-markup language, used to create markup languages such as DocBook.",
                        "GlossSeeAlso": ["GML", "XML"]
                    },
                    "GlossSee": "markup"
                }
            }
        }
    }
}';

$b ='{
    "entry1": {
        "entry2": {
            "title": 2,
            "entry3": {
                "title": 4,
                "title" : 5
            }
        }
    }
}';


$json1 = json_decode($a);
$json2 = json_decode($b);


var_dump($json1);
var_dump($json2);

Output

object(stdClass)#6 (1) {
  ["glossary"]=>
  object(stdClass)#1 (2) {
    ["title"]=>
    string(16) "example glossary"
    ["GlossDiv"]=>
    object(stdClass)#2 (2) {
      ["title"]=>
      string(1) "S"
      ["GlossList"]=>
      object(stdClass)#5 (1) {
        ["GlossEntry"]=>
        object(stdClass)#3 (7) {
          ["ID"]=>
          string(4) "SGML"
          ["SortAs"]=>
          string(4) "SGML"
          ["GlossTerm"]=>
          string(36) "Standard Generalized Markup Language"
          ["Acronym"]=>
          string(4) "SGML"
          ["Abbrev"]=>
          string(13) "ISO 8879:1986"
          ["GlossDef"]=>
          object(stdClass)#4 (2) {
            ["para"]=>
            string(72) "A meta-markup language, used to create markup languages such as DocBook."
            ["GlossSeeAlso"]=>
            array(2) {
              [0]=>
              string(3) "GML"
              [1]=>
              string(3) "XML"
            }
          }
          ["GlossSee"]=>
          string(6) "markup"
        }
      }
    }
  }
}
object(stdClass)#10 (1) {
  ["entry1"]=>
  object(stdClass)#9 (1) {
    ["entry2"]=>
    object(stdClass)#7 (2) {
      ["title"]=>
      int(2)
      ["entry3"]=>
      object(stdClass)#8 (1) {
        ["title"]=>
        int(5)
      }
    }
  }
}

Correct me if I am wrong