php教程

assert

(PHP 4, PHP 5, PHP 7)

assert — 检查一个断言是否为 FALSE

说明

PHP 5

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

PHP 7

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

assert() 会检查指定的 assertion 并在结果为 FALSE 时采取适当的行动。

Traditional assertions (PHP 5 and 7)

如果 assertion 是字符串，它将会被 assert() 当做 PHP 代码来执行。 assertion 是字符串的优势是当禁用断言时它的开销会更小，并且在断言失败时消息会包含 assertion 表达式。 这意味着如果你传入了 boolean 的条件作为 assertion，这个条件将不会显示为断言函数的参数；在调用你定义的 assert_options() 处理函数时，条件会转换为字符串，而布尔值 FALSE 会被转换成空字符串。

断言这个功能应该只被用来调试。 你应该用于完整性检查时测试条件是否始终应该为 TRUE，来指示某些程序错误，或者检查具体功能的存在（类似扩展函数或特定的系统限制和功能）。

断言不应该用于普通运行时操作，类似输入参数的检查。 作为一个经验法则，在断言禁用时你的代码也应该能够正确地运行。

assert() 的行为可以通过 assert_options() 来配置，或者手册页面上描述的 .ini 设置。

assert_options() ASSERT_CALLBACK 配置指令允许设置回调函数来处理失败的断言。

assert() 回调函数在构建自动测试套件的时候尤其有用，因为它们允许你简易地捕获传入断言的代码，并包含断言的位置信息。 当信息能够被其他方法捕获，使用断言可以让它更快更方便！

回调函数应该接受三个参数。 第一个参数包括了断言失败所在的文件。 第二个参数包含了断言失败所在的行号，第三个参数包含了失败的表达式（如有任意 — 字面值例如 1 或者 "two" 将不会传递到这个参数）。 PHP 5.4.8 及更高版本的用户也可以提供第四个可选参数，如果设置了，用于将 description 指定到 assert()。

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)

参数

assertion

断言。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

如果 assertion 失败了，选项 description 将会包括在失败信息里。

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.

返回值

assertion 是 false 则返回 FALSE，否则是 TRUE。

更新日志

版本 说明
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 增加了参数 description。 description 现在也作为第四个参数提供给 ASSERT_CALLBACK 模式里的回调函数。

范例

Traditional assertions (PHP 5 and 7)

Example #1 使用自定义处理程序处理失败的断言

<?php
// 激活断言，并设置它为 quiet
assert_options(ASSERT_ACTIVE, 1);
assert_options(ASSERT_WARNING, 0);
assert_options(ASSERT_QUIET_EVAL, 1);

//创建处理函数
function my_assert_handler($file, $line, $code)
{
    echo "<hr>Assertion Failed:
        File '$file'<br />
        Line '$line'<br />
        Code '$code'<br /><hr />";
}

// 设置回调函数
assert_options(ASSERT_CALLBACK, 'my_assert_handler');

// 让一则断言失败
assert('mysql_query("")');
?>

Example #2 使用自定义处理器打印描述信息

<?php
// 激活断言，并设置它为 quiet
assert_options(ASSERT_ACTIVE, 1);
assert_options(ASSERT_WARNING, 0);
assert_options(ASSERT_QUIET_EVAL, 1);

//创建处理函数
function my_assert_handler($file, $line, $code, $desc = null)
{
    echo "Assertion failed at $file:$line: $code";
    if ($desc) {
        echo ": $desc";
    }
    echo "\n";
}

// 设置回调函数
assert_options(ASSERT_CALLBACK, 'my_assert_handler');

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

以上例程会输出：

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

参见

User Contributed Notes

jason at jaypha dot com 29-Dec-2017 11:13
You can take advantage of how assert is handled to use it for crude conditional compilation.

For example

<?php
  assert(print("Some debug message\n"));
  assert(($val = "dev") || true);
?>

Since print() always returns 1, the topmost assertion will pass. For others, you may need to add a || true. Always enclose the expression in ().

In a development environment where zend.assertions=1, the above code will execute. In production environments where zend.assertions=-1, it wont even compile, thus not burdening performance.

Another, more real world, example.

<?php
  $cssSrc = 'https://code.jquery.com/jquery-3.2.1.min.js';
  assert(($cssSrc = 'http://dev.local/jquery-3.2.1.js') || true);
  echo "<link rel='stylesheet' type='text/css' href='$cssSrc'/>\n";
?>

In a production environment, The website will use the minified version from the CDN. In a development environment, a development version, sourced locally, will be used instead.

Note: This will not work for everything. Only code that can be embedded in an expression will work.
Ben 26-Aug-2016 09:51
if there was no 'warning' message when assertion failed (FALSE), try reset the error handler:
<?php
set_error_handler ( null );
office dot stojmenovic at gmail dot com 20-Sep-2013 12:35
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);

?>
uramihsayibok, gmail, com 20-Jun-2010 01:48
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)
hodgman at ali dot com dot au 28-Jul-2008 09:19
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.
Krzysztof &#39;ChanibaL&#39; Bociurko 01-Oct-2007 06:13
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...)
mail<at>aaron-mueller.de 13-Sep-2006 10:51
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);

?>

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