Checks if assertion is FALSE

assert_options
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PHP Options/Info Functions
PHP Manual

# assert

(PHP 4, PHP 5, PHP 7)

assert — Checks if assertion is `FALSE`

### Description

PHP 5

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

### See Also

- assert_options() - Set/get the various assert flags

assert_options
cli_get_process_title
PHP Options/Info Functions
PHP Manual