assert

(PHP 4, PHP 5, PHP 7)

assert — Checks if assertion is FALSE

Description

PHP 5 and 7

bool assert ( mixed $assertion [, string $description ] )

PHP 7

bool assert ( mixed $assertion [, Throwable $exception ] )

assert() will check the given assertion and take appropriate action if its result is FALSE.

Traditional assertions (PHP 5 and 7)

If the assertion is given as a string it will be evaluated as PHP code by assert(). The advantages of a string assertion are less overhead when assertion checking is off and messages containing the assertion expression when an assertion fails. This means that if you pass a boolean condition as assertion this condition will not show up as parameter to the assertion function which you may have defined with the assert_options() function, the condition is converted to a string before calling that handler function, and the boolean FALSE is converted as the empty string.

Assertions should be used as a debugging feature only. You may use them for sanity-checks that test for conditions that should always be TRUE and that indicate some programming errors if not or to check for the presence of certain features like extension functions or certain system limits and features.

Assertions should not be used for normal runtime operations like input parameter checks. As a rule of thumb your code should always be able to work correctly if assertion checking is not activated.

The behavior of assert() may be configured by assert_options() or by .ini-settings described in that functions manual page.

The assert_options() function and/or ASSERT_CALLBACK configuration directive allow a callback function to be set to handle failed assertions.

assert() callbacks are particularly useful for building automated test suites because they allow you to easily capture the code passed to the assertion, along with information on where the assertion was made. While this information can be captured via other methods, using assertions makes it much faster and easier!

The callback function should accept three arguments. The first argument will contain the file the assertion failed in. The second argument will contain the line the assertion failed on and the third argument will contain the expression that failed (if any — literal values such as 1 or "two" will not be passed via this argument). Users of PHP 5.4.8 and later may also provide a fourth optional argument, which will contain the description given to assert(), if it was set.

Expectations (PHP 7 only)

assert() is a language construct in PHP 7, allowing for the definition of expectations: assertions that take effect in development and testing environments, but are optimised away to have zero cost in production.

While assert_options() can still be used to control behaviour as described above for backward compatibility reasons, PHP 7 only code should use the two new configuration directives to control the behaviour of assert() and not call assert_options().

PHP 7 configuration directives for **assert()**
Directive	Default value	Possible values
zend.assertions	1	1: generate and execute code (development mode) 0: generate code but jump around it at runtime -1: do not generate code (production mode)
assert.exception	0	1: throw when the assertion fails, either by throwing the object provided as the `exception` or by throwing a new AssertionError object if `exception` wasn't provided 0: use or generate a Throwable as described above, but only generate a warning based on that object rather than throwing it (compatible with PHP 5 behaviour)

Parameters

assertion: The assertion. In PHP 5, this must be either a string to be evaluated or a boolean to be tested. In PHP 7, this may also be any expression that returns a value, which will be executed and the result used to indicate whether the assertion succeeded or failed.
description: An optional description that will be included in the failure message if the assertion fails.
exception: In PHP 7, the second parameter can be a Throwable object instead of a descriptive string, in which case this is the object that will be thrown if the assertion fails and the assert.exception configuration directive is enabled.

Return Values

FALSE if the assertion is false, TRUE otherwise.

Changelog

Version	Description
7.0.0	assert() is now a language construct and not a function. assertion() can now be an expression. The second parameter is now interpreted either as an `exception` (if a Throwable object is given), or as the `description` supported from PHP 5.4.8 onwards.
5.4.8	The `description` parameter was added. The `description` is also now provided to a callback function in `ASSERT_CALLBACK` mode as the fourth argument.

Examples

Traditional assertions (PHP 5 and 7)

Example #1 Handle a failed assertion with a custom handler


<?php
// Active assert and make it quiet
assert_options(ASSERT_ACTIVE, 1);
assert_options(ASSERT_WARNING, 0);
assert_options(ASSERT_QUIET_EVAL, 1);

// Create a handler function
function my_assert_handler($file, $line, $code)
{
    echo "<hr>Assertion Failed:
        File '$file'<br />
        Line '$line'<br />
        Code '$code'<br /><hr />";
}

// Set up the callback
assert_options(ASSERT_CALLBACK, 'my_assert_handler');

// Make an assertion that should fail
assert('mysql_query("")');
?>

Example #2 Using a custom handler to print a description


<?php
// Active assert and make it quiet
assert_options(ASSERT_ACTIVE, 1);
assert_options(ASSERT_WARNING, 0);
assert_options(ASSERT_QUIET_EVAL, 1);

// Create a handler function
function my_assert_handler($file, $line, $code, $desc = null)
{
    echo "Assertion failed at $file:$line: $code";
    if ($desc) {
        echo ": $desc";
    }
    echo "\n";
}

// Set up the callback
assert_options(ASSERT_CALLBACK, 'my_assert_handler');

// Make an assertion that should fail
assert('2 < 1');
assert('2 < 1', 'Two is less than one');
?>

The above example will output:

 Assertion failed at test.php:21: 2 < 1
 Assertion failed at test.php:22: 2 < 1: Two is less than one

Expectations (PHP 7 only)

Example #3 Expectations without a custom exception


<?php
assert(true == false);
echo 'Hi!';
?>

With zend.assertions set to 0, the above example will output:

Hi!

With zend.assertions set to 1 and assert.exception set to 0, the above example will output:

Warning: assert(): assert(true == false) failed in - on line 2
Hi!

With zend.assertions set to 1 and assert.exception set to 1, the above example will output:

Fatal error: Uncaught AssertionError: assert(true == false) in -:2
Stack trace:
#0 -(2): assert(false, 'assert(true == ...')
#1 {main}
  thrown in - on line 2

Example #4 Expectations with a custom exception


<?php
class CustomError extends AssertionError {}

assert(true == false, new CustomError('True is not false!'));
echo 'Hi!';
?>

With zend.assertions set to 0, the above example will output:

Hi!

With zend.assertions set to 1 and assert.exception set to 0, the above example will output:

Warning: assert(): CustomError: True is not false! in -:4
Stack trace:
#0 {main} failed in - on line 4
Hi!

With zend.assertions set to 1 and assert.exception set to 1, the above example will output:

Fatal error: Uncaught CustomError: True is not false! in -:4
Stack trace:
#0 {main}
  thrown in - on line 4

User Contributed Notes

uramihsayibok, gmail, com

5 years ago


There's a nice advantage to giving assert() some code to execute, as a string, rather than a simple true/false value: commenting.

<?php

assert('is_int($int) /* $int parameter must be an int, not just numeric */');

// and my personal favorite
assert('false /* not yet implemented */');

?>

The comment will show up in the output (or in your assertion handler) and doesn't require someone debugging to go through your code trying to figure out why the assertion happened. That's no excuse to not comment your code, of course.

You need to use a block comment (/*...*/) because a line comment (//...) creates an "unexpected $end" parse error in the evaluated code. Bug? Could be.
(You can get around it with "false // not yet implemented\n" but that screws up the message)

Krzysztof 'ChanibaL' Bociurko

8 years ago


Note that func_get_args() should be used carefully and never in a string! For example:

<?php
function asserted_normal($a, $b) {
    assert(var_dump(func_get_args()));
    }
function asserted_string($a, $b) {
    assert('var_dump(func_get_args())');
    }
?>

<?php asserted_normal(1,2) ?> prints
array(2) {
  [0]=>
  int(1)
  [1]=>
  int(2)
}

but <?php asserted_string(3,4) ?> prints
array(1) {
  [0]=>
  string(25) "var_dump(func_get_args())"
}

This is because of that the string passed to assert() is being evaled inside assert, and not your function. Also, note that this works correctly, because of the eval scope:

<?php
function asserted_evaled_string($a, $b) {
    assert(eval('var_dump(func_get_args())'));
    }
asserted_evaled_string(5,6);
?>
array(2) {
  [0]=>
  int(5)
  [1]=>
  int(6)
}

(oh, and for simplicity's sake the evaled code doesn't return true, so  don't worry that it fails assertion...)

hodgman at ali dot com dot au

7 years ago


As noted on Wikipedia - "assertions are primarily a development tool, they are often disabled when a program is released to the public." and "Assertions should be used to document logically impossible situations and discover programming errors— if the 'impossible' occurs, then something fundamental is clearly wrong. This is distinct from error handling: most error conditions are possible, although some may be extremely unlikely to occur in practice. Using assertions as a general-purpose error handling mechanism is usually unwise: assertions do not allow for graceful recovery from errors, and an assertion failure will often halt the program's execution abruptly. Assertions also do not display a user-friendly error message."

This means that the advice given by "gk at proliberty dot com" to force assertions to be enabled, even when they have been disabled manually, goes against best practices of only using them as a development tool.

devoto13 at gmail dot com

2 years ago


"If you would like to compare with === or !== you need to add '(string)' before string numbers. Or wrap them with quotes."

Do not use this aproach, because it would not work, look at http://php.net/manual/en/function.var-export.php .

mail<at>aaron-mueller.de

9 years ago


Here is a simple demonstration of Design By Contract with PHP

<?php

assert_options(ASSERT_ACTIVE, 1);
assert_options(ASSERT_WARNING, 0);
assert_options(ASSERT_BAIL, 1);
assert_options(ASSERT_CALLBACK, 'dcb_callback');

function dcb_callback($script, $line, $message) {
    echo "<h1>Condition failed!</h1><br />
        Script: <strong>$script</strong><br />
        Line: <strong>$line</strong><br />
        Condition: <br /><pre>$message</pre>";
}

// Parameters
$a = 5;
$b = 'Simple DCB with PHP';

// Pre-Condition
assert('
    is_integer($a) &&
    ($a > 0) &&
    ($a < 20) &&
    
    is_string($b) &&
    (strlen($b) > 5);
');

// Function
function combine($a, $b) {
    return "Kombined: " . $b . $a;
}

$result = combine($a, $b);

// Post-Condition
assert('
    is_string($result) &&
    (strlen($result) > 0);
');

// All right, the Function works fine
var_dump($result);

?>

office dot stojmenovic at gmail dot com

2 years ago


Example from Ikac Framework how they use assert()

<?php

    /**
     * Set Assertion Debug
     * 
     * This method will check the given assertion and take appropriate -
     * action if its result is FALSE. 
     * 
     * This file is part of Ikac Framework.
     * 
     * @package Ikac Framework
     * @author Ivan Stojmenovic Ikac <contact.@stojmenovic.info>
     * 
     * @param mixed $assertion  The assertion.
     * @param mixed $callback Callback to call on failed assertions
     * @param array $options  Set the various control options or just query their current settings. 
     * @param string $description  An optional description that will be included in the failure message if the assertion fails. 
     */
    public function setAssertionDebug($assertion, $callback, array $options, $description = null)
    {
        if (is_array($options)) {
            foreach ($options AS $option => $value) {
                assert_options($option, $value);
            }
        }
        if ($callback) {
            assert_options(ASSERT_CALLBACK, $callback);
        }
        
        return assert($assertion, $description);
    }
    ?>

How to use:

<?php
      use Ikac\Component\SystemBehaviour\OptionsInfo;

      $system = new OptionsInfo();

      $option = array(ASSERT_ACTIVE => 1,ASSERT_WARNING => 0,ASSERT_QUIET_EVAL => 1);

     $system->setAssertionDebug('2<1', function(){
            echo "Assertion failed";
     }, $option);

?>

gk at proliberty dot com

10 years ago


If you expect your code to be able to work well with other code, then you should not make any assumptions about the current state of assert_options() flags, prior to calling assert(): other code may disable ASSERT_ACTIVE, without you knowing it - this would render assert() useless!



To avoid this, ALWAYS set assert_options() IMMEDIATELY before calling assert(), per the C++ paradigm for assertion usage:



In one C++ source file, you can define and undefine NDEBUG multiple times, each time followed by #include <cassert>, to enable or disable the assert macro multiple times in the same source file.



Here is how I workaround this issue in my PHP code: 



<?php

//////////////////////////////////////////////////////////////////////

/// phpxAssertHandler_f 

//////////////////////////////////////////////////////////////////////

/**

 * @desc     Handler which also sets up assert options if not being called as handler

                 Always fatal when assertion fails

                 Always make sure assertion is enabled

                 Cannot depend on other code not using assert or using its own assert handler!

            USAGE:

            // customize error level of assertion (php assert_options() only allows E_WARNING or nothing at all):

                phpxAssertHandler_f(E_USER_NOTICE); 

            // control assertion active state: not dependent on anything another piece of code might do with ASSERT_ACTIVE

                $GLOBALS['MY_ASSERT_ACTIVE']=false;

                phpxAssertHandler_f(E_USER_NOTICE,$GLOBALS['MY_ASSERT_ACTIVE']); 

            // use alternate assertion callback function:

            // NOTE: pass null as custom options parameter to use default options

            // NOTE: pass no values for assert options parameter array elements to use default options

                $GLOBALS['MY_ASSERT_ACTIVE']=false;

                $GLOBALS['MY_ASSERT_CALLBACK']='myAssertCallback';

                phpxAssertHandler_f(

                    null,

                    array(

                        0=>$GLOBALS['MY_ASSERT_ACTIVE'],

                        3=>$GLOBALS['MY_ASSERT_CALLBACK'],

                    )

                ); 

                 

 * @param   mixed = file or options

 * @param   line

 * @param   code

 * @return   void

 */

function phpxAssertHandler_f($file_or_custom_options=null, $line_or_assert_options=null, $code=null){



    static $custom_options;

    $debug = false;



    if (is_null($code)){

        // set default assert_options

        $assert_options[]=1;//ASSERT_ACTIVE

        $assert_options[]=0;//ASSERT_WARNING - 

        $assert_options[]=0;//ASSERT_QUIET_EVAL

        $assert_options[]=__FUNCTION__;//ASSERT_CALLBACK        



        // set default custom_options

        $custom_options[]=E_USER_ERROR;// error level            



        if (!is_null($line_or_assert_options)){

            // assert_options are passed in

            if (!is_array($line_or_assert_options)){

                $line_or_assert_options=array($line_or_assert_options);

            }

            foreach ($line_or_assert_options as $i=>$assert_option){

                if ($assert_option===true) $assert_option=1;

                if ($assert_option===false) $assert_option=0;

                $assert_options[$i]=$assert_option;

                if($debug) echo ("assert_options[$i]=$assert_option\n");

            }

        }



        if (!is_null($file_or_custom_options)){

            // custom_options are passed in

            if (!is_array($file_or_custom_options)){

                $file_or_custom_options=array($file_or_custom_options);

            }

            foreach ($file_or_custom_options as $i=>$custom_option){

                if ($custom_option===true) $custom_option=1;

                if ($custom_option===false) $custom_option=0;

                $custom_options[$i]=$custom_option;

                if($debug) echo ("custom_options[$i]=$custom_option\n");

            }

        }



        // set assert options

        @assert_options (ASSERT_ACTIVE, $assert_options[0]); 

        @assert_options (ASSERT_WARNING, $assert_options[1]); 

        @assert_options (ASSERT_QUIET_EVAL, $assert_options[2]); 

        @assert_options (ASSERT_CALLBACK, $assert_options[3]);         



    } else {

    // we are acting as a callback function

        $file = $file_or_custom_options;

        $line = $line_or_assert_options;

        $msg="ASSERTION FAILED: $code"; 

        phpxErrorHandler_f ($custom_options[0],$msg,$file,$line);

    }

}//phpxAssertHandler_f()

?>

fabiano dot fa04 at gmail dot com

2 years ago


You can also use a function instead a string description as the second parameter.

<?php

    function assertIsFalse(){
        echo "Hey, this assert is false and I'm a function.";
    }

    $foo = "foo";
    $bar = $foo;

    $foo = "bar";

    assert( $foo == $bar, assertIsFalse() );

?>

The result would be:

Hey, this assert is false and I'm a function.

assert

Description

Traditional assertions (PHP 5 and 7)

Expectations (PHP 7 only)

Parameters

Return Values

Changelog

Examples

Traditional assertions (PHP 5 and 7)

Expectations (PHP 7 only)

See Also

User Contributed Notes