php - PHP assert() 是如何工作的？

Question

我试图做一个简单的 PHP 断言来验证一个字符串不是空的，但是得到了令人困惑的结果。

我不知道 assert() 中的字符串评估功能，但检查了文档并理解了那部分。

我将代码包含在所有测试用例中，然后是输出，然后是问题。当案例因语法错误而失败时，我只需将其注释掉并重复测试，以便可以执行以下案例，并显示每次执行的输出。

该代码是关于使用 XMLReader 定位 XML 元素的，但这恰好是我的代码。所以这里首先是代码：

<?php

$xml = <<< XML
<depts  xmlns:apl="urn:my:ns" >
    <apl:dept>Dept One</apl:dept>
    <apl:dept>Dept Tow</apl:dept>
</depts>
XML;


$elmLocal = 'dept';
$elmUrn = "urn:my:ns";

$xr = new XMLReader;
$xr->XML($xml);

// move to the first desired element node
$found = false;
while ($xr->read()) {
    if ($xr->localName === $elmLocal && $xr->namespaceURI === $elmUrn) {
        $found = true;
        break;
    }
}
if (!$found) {
    exit("---Error--- No element found with given Name/NS.\n");
}



$var = $xr->name;

echo "---------------- Test Results ---------------->\n";

echo "----- var    =={$var}==\n";
echo "----- xr name=={$xr->name}==\n\n";


echo "------ assertion 00 ------>\n";
assert ($xr->name);

echo "------ assertion 01 ------>\n";
assert ($var);

echo "------ assertion 02 ------>\n";
assert ('$xr->name!==""');   

echo "------ assertion 03 ------>\n";
assert ('$var!==""');   

echo "------ assertion 04 ------>\n";
assert ("{$xr->name}!==''");   

echo "------ assertion 05 ------>\n";
assert ("{$var}!==''");   

echo "------ assertion 06 ------>\n";
assert(!empty($xr->name));

echo "------ assertion 07 ------>\n";
assert(!empty($var));

echo "------ assertion 08 ------>\n";
assert('!empty($xr->name)');

echo "------ assertion 09 ------>\n";
assert('!empty($var)');

echo "------ assertion 10 ------>\n";
assert("!empty({$xr->name})");

echo "------ assertion 11 ------>\n";
assert("!empty({$var})");



// do some processing
$domNode = $xr->expand(); // DOMNode XMLReader::expand ([ DOMNode $basenode ] )


?>

这里是执行输出 - 再次注意有对致命语法错误和重复执行的注释，您可以假设每个断言都单独测试：

#tests#php -v
PHP 5.3.3-7+squeeze3 with Suhosin-Patch (cli) (built: Jun 28 2011 13:13:26)
Copyright (c) 1997-2009 The PHP Group
Zend Engine v2.3.0, Copyright (c) 1998-2010 Zend Technologies
    with Xdebug v2.1.0, Copyright (c) 2002-2010, by Derick Rethans
    with Suhosin v0.9.32.1, Copyright (c) 2007-2010, by SektionEins GmbH


#tests#php -q vars.php
---------------- Test Results ---------------->
----- var    ==apl:dept==
----- xr name==apl:dept==

------ assertion 00 ------>
PHP Parse error:  syntax error, unexpected ':' in /shared/tests/vars.php(40) : assert code on line 1
PHP Stack trace:
PHP   1. {main}() /shared/tests/vars.php:0
PHP   2. assert() /shared/tests/vars.php:40
PHP Catchable fatal error:  assert(): Failure evaluating code:
apl:dept in /shared/tests/vars.php on line 40
PHP Stack trace:
PHP   1. {main}() /shared/tests/vars.php:0
PHP   2. assert() /shared/tests/vars.php:40

#tests#php -q vars.php
---------------- Test Results ---------------->
----- var    ==apl:dept==
----- xr name==apl:dept==

------ assertion 01 ------>
PHP Parse error:  syntax error, unexpected ':' in /shared/tests/vars.php(43) : assert code on line 1
PHP Stack trace:
PHP   1. {main}() /shared/tests/vars.php:0
PHP   2. assert() /shared/tests/vars.php:43
PHP Catchable fatal error:  assert(): Failure evaluating code:
apl:dept in /shared/tests/vars.php on line 43
PHP Stack trace:
PHP   1. {main}() /shared/tests/vars.php:0
PHP   2. assert() /shared/tests/vars.php:43

#tests#php -q vars.php
---------------- Test Results ---------------->
----- var    ==apl:dept==
----- xr name==apl:dept==

------ assertion 02 ------>
------ assertion 03 ------>
------ assertion 04 ------>
PHP Parse error:  syntax error, unexpected ':' in /shared/tests/vars.php(52) : assert code on line 1
PHP Stack trace:
PHP   1. {main}() /shared/tests/vars.php:0
PHP   2. assert() /shared/tests/vars.php:52
PHP Catchable fatal error:  assert(): Failure evaluating code:
apl:dept!=='' in /shared/tests/vars.php on line 52
PHP Stack trace:
PHP   1. {main}() /shared/tests/vars.php:0
PHP   2. assert() /shared/tests/vars.php:52

#tests#php -q vars.php
---------------- Test Results ---------------->
----- var    ==apl:dept==
----- xr name==apl:dept==

------ assertion 02 ------>
------ assertion 03 ------>
------ assertion 05 ------>
PHP Parse error:  syntax error, unexpected ':' in /shared/tests/vars.php(55) : assert code on line 1
PHP Stack trace:
PHP   1. {main}() /shared/tests/vars.php:0
PHP   2. assert() /shared/tests/vars.php:55
PHP Catchable fatal error:  assert(): Failure evaluating code:
apl:dept!=='' in /shared/tests/vars.php on line 55
PHP Stack trace:
PHP   1. {main}() /shared/tests/vars.php:0
PHP   2. assert() /shared/tests/vars.php:55

#tests#php -q vars.php
---------------- Test Results ---------------->
----- var    ==apl:dept==
----- xr name==apl:dept==

------ assertion 02 ------>
------ assertion 03 ------>
------ assertion 06 ------>
PHP Warning:  assert(): Assertion failed in /shared/tests/vars.php on line 58
PHP Stack trace:
PHP   1. {main}() /shared/tests/vars.php:0
PHP   2. assert() /shared/tests/vars.php:58
------ assertion 07 ------>
------ assertion 08 ------>
PHP Warning:  assert(): Assertion "!empty($xr->name)" failed in /shared/tests/vars.php on line 64
PHP Stack trace:
PHP   1. {main}() /shared/tests/vars.php:0
PHP   2. assert() /shared/tests/vars.php:64
------ assertion 09 ------>
------ assertion 10 ------>
PHP Parse error:  syntax error, unexpected ':', expecting T_PAAMAYIM_NEKUDOTAYIM in /shared/tests/vars.php(70) : assert code on line 1
PHP Stack trace:
PHP   1. {main}() /shared/tests/vars.php:0
PHP   2. assert() /shared/tests/vars.php:70
PHP Catchable fatal error:  assert(): Failure evaluating code:
!empty(apl:dept) in /shared/tests/vars.php on line 70
PHP Stack trace:
PHP   1. {main}() /shared/tests/vars.php:0
PHP   2. assert() /shared/tests/vars.php:70

#tests#php -q vars.php
---------------- Test Results ---------------->
----- var    ==apl:dept==
----- xr name==apl:dept==

------ assertion 02 ------>
------ assertion 03 ------>
------ assertion 06 ------>
PHP Warning:  assert(): Assertion failed in /shared/tests/vars.php on line 58
PHP Stack trace:
PHP   1. {main}() /shared/tests/vars.php:0
PHP   2. assert() /shared/tests/vars.php:58
------ assertion 07 ------>
------ assertion 08 ------>
PHP Warning:  assert(): Assertion "!empty($xr->name)" failed in /shared/tests/vars.php on line 64
PHP Stack trace:
PHP   1. {main}() /shared/tests/vars.php:0
PHP   2. assert() /shared/tests/vars.php:64
------ assertion 09 ------>
------ assertion 11 ------>
PHP Parse error:  syntax error, unexpected ':', expecting T_PAAMAYIM_NEKUDOTAYIM in /shared/tests/vars.php(73) : assert code on line 1
PHP Stack trace:
PHP   1. {main}() /shared/tests/vars.php:0
PHP   2. assert() /shared/tests/vars.php:73
PHP Catchable fatal error:  assert(): Failure evaluating code:
!empty(apl:dept) in /shared/tests/vars.php on line 73
PHP Stack trace:
PHP   1. {main}() /shared/tests/vars.php:0
PHP   2. assert() /shared/tests/vars.php:73

现在发表一些评论：

案例 1,2 是可以理解的 - 即字符串评估“功能”。

所有带有双引号括起来的断言表达式的情况 - 也弄清楚了：首先完成变量解析，这导致执行中的语法错误。因此，为了使案例 4 例如工作，我们可以这样做：

echo "------ assertion 04 ------>\n";
assert ("'{$xr->name}'!==''");

现在真正的问题是案例 6,7。为什么 6 失败而 7 成功。案例 8,9 - 8 失败，而 9 成功。

问候。

score 2 · Accepted Answer

这与 assert() 的工作方式无关，而与 empty() 的工作方式有关。
当与$object->inaccessiblePropempty 一起使用时，首先尝试与 isset() 相同的操作，如果此“测试”返回 false，则 empty() 甚至不尝试访问元素而是返回 true。
而且 XMLReader 类显然没有按照您需要的方式实现__isset()方法。

<?php
$xml = <<< XML
<depts  xmlns:apl="urn:my:ns" >
    <apl:dept>Dept One</apl:dept>
    <apl:dept>Dept Tow</apl:dept>
</depts>
XML;

$elmLocal = 'dept';
$elmUrn = "urn:my:ns";

$xr = new XMLReader;
$xr->XML($xml);

// move to the first desired element node
$found = false;
while ($xr->read()) {
    if ($xr->localName === $elmLocal && $xr->namespaceURI === $elmUrn) {
        $found = true;
        break;
    }
}
if (!$found) {
    exit("---Error--- No element found with given Name/NS.\n");
}

$var = $xr->name;
var_dump(isset($xr->name));
var_dump(empty($xr->name));
echo $xr->name;

印刷

bool(false)
bool(true)
apl:dept

score 0 · Accepted Answer

Now the real issue is with cases 6,7. Why is 6 failing while 7 is succeeding. The same with cases 8,9 - 8 failing while 9 succeeding.

因为它不是标量类型。

php - PHP assert() 是如何工作的？

2 回答 2

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