检查一个断言是否为 FALSE

说明

PHP 5

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

PHP 7

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

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

assert_options() - 设置/获取断言的各种标志