You want to inspect the values stored in a variable. It may be a complicated nested array or object, so you can’t just print it out or loop through it.
Use var_dump(), print_r(), or var_export(), depending on exactly what you need.
The var_dump() and print_r() functions provide different human-readable representations of variables.
The print_r() function is a little more concise:
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$info = array('name' => 'frank', 12.6, array(3, 4)); print_r($info); |
prints:
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Array ( [name] => frank [0] => 12.6 [1] => Array ( [0] => 3 [1] => 4 ) ) |
While this:
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$info = array('name' => 'frank', 12.6, array(3, 4)); var_dump($info); |
prints:
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array(3) { ["name"]=> string(5) "frank" [0]=> float(12.6) [1]=> array(2) { [0]=> int(3) [1]=> int(4) } } |
The var_export() function produces valid PHP code that, when executed, defines the exported variable:
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$info = array('name' => 'frank', 12.6, array(3, 4)); var_export($info); |
prints:
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array ( 'name' => 'frank', 0 => 12.6, 1 => array ( 0 => 3, 1 => 4, ), ) |
The three functions mentioned in the Solution differ in how they handle recursion in references.
Because these functions recursively work their way through variables, if you have references within a variable pointing back to the variable itself, you would end up with an infinite loop unless these functions bailed out.
When var_dump() or print_r() has seen a variable once, it prints *RECURSION* instead of printing information about the variable again and continues iterating through the rest of the information it has to print.
The var_export() function does a similar thing, but it prints null instead of *RECURSION* to ensure its output is executable PHP code.
Consider the arrays $user_1 and $user_2, which reference each other through their friend elements:
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$user_1 = array('name' => 'Max Bialystock', 'username' => 'max'); $user_2 = array('name' => 'Leo Bloom', 'username' => 'leo'); // Max and Leo are friends $user_2['friend'] = &$user_1; $user_1['friend'] = &$user_2; // Max and Leo have jobs $user_1['job'] = 'Swindler'; $user_2['job'] = 'Accountant'; |
The output of print_r($user_2) is:
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Array ( [name] => Leo Bloom [username] => leo [friend] => Array ( [name] => Max Bialystock [username] => max [friend] => Array ( [name] => Leo Bloom [username] => leo [friend] => Array *RECURSION* [job] => Accountant ) [job] => Swindler ) [job] => Accountant ) |
When print_r() sees the reference to $user_1 the second time, it prints *RECUR SION* instead of descending into the array. It then continues on its way, printing the remaining elements of $user_1 and $user_2.
The var_dump() function behaves similarly:
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array(4) { ["name"]=> string(9) "Leo Bloom" ["username"]=> string(3) "leo" ["friend"]=> &array(4) { ["name"]=> string(14) "Max Bialystock" ["username"]=> string(3) "max" ["friend"]=> &array(4) { ["name"]=> string(9) "Leo Bloom" ["username"]=> string(3) "leo" ["friend"]=> *RECURSION* ["job"]=> string(10) "Accountant" } ["job"]=> string(8) "Swindler" } ["job"]=> string(10) "Accountant" } |
As does var_export(), but with null instead of *RECURSION*:
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array ( 'name' => 'Leo Bloom', 'username' => 'leo', 'friend' => array ( 'name' => 'Max Bialystock', 'username' => 'max', 'friend' => array ( 'name' => 'Leo Bloom', 'username' => 'leo', 'friend' => NULL, 'job' => 'Accountant', ), 'job' => 'Swindler', ), 'job' => 'Accountant', ) |
The print_r() and var_export() functions accept a second argument which, if set to true tells the functions to return the string representation of the variable rather than printing it.
To capture the output from var_dump(), however, you need to use output buffering:
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ob_start(); var_dump($user); $dump = ob_get_contents(); ob_end_clean(); |
This puts the results of var_dump($user) in $dump.
