xml xpath不返回节点值

Question

我有一个测试文件，我试图用SimpleXML的xpath方法分析一个xml字符串。

当我尝试直接使用xpath访问节点值时，我得到空输出，但是当我使用xpath抓取元素并通过它们循环时，它工作正常。

当我看文档时，似乎我的语法应该工作。有什么我失踪？

<?php 

$xmlstring = '<?xml version="1.0" encoding="iso-8859-1"?> 
<users> 
    <user> 
    <firstname>Sheila</firstname> 
    <surname>Green</surname> 
    <address>2 Good St</address> 
    <city>Campbelltown</city> 
    <country>Australia</country> 
    <contact> 
     <phone type="mobile">1234 1234</phone> 
     <url>http://example.com</url> 
     <email>pamela@example.com</email> 
    </contact> 
    </user> 
    <user> 
    <firstname>Bruce</firstname> 
    <surname>Smith</surname> 
    <address>1 Yakka St</address> 
    <city>Meekatharra</city> 
    <country>Australia</country> 
    <contact> 
     <phone type="landline">4444 4444</phone> 
     <url>http://yakka.example.com</url> 
     <email>bruce@yakka.example.com</email> 
    </contact> 
    </user> 
</users>'; 


// Start parsing 
if(!$xml = simplexml_load_string($xmlstring)){ 
    echo "Error loading string "; 
} else { 
    echo "<pre>"; 

    // Print all firstname values directly from xpath 
    // This outputs the elements, but the values are blank 
    print_r($xml->xpath("https://stackoverflow.com/users/user/firstname")); 

    // Set a variable with all of the user elements and then loop through and print firstname values 
    // This DOES output the values 
    $users = $xml->xpath("https://stackoverflow.com/users/user"); 
    foreach($users as $user){ 
     echo $user->firstname; 
    } 

    // Find all firstname values by tag 
    // This does not output the values 
    print_r($xml->xpath("//firstname")); 
    echo "</pre>"; 
} 

Answer 1

作为每手动http://uk1.php.net/manual/en/simplexmlelement.xpath.php

中的XPath方法搜索儿童匹配XPath路径的SimpleXML节点。

在第一个和第三个示例中，您将返回包含节点值的数组的对象，而不是节点本身。所以你无法做到如

$results = $xml->xpath("//firstname"); 
foreach ($results as $result) { 
    echo $result->firstname; 
} 

相反，您可以直接回显该值。那么，几乎直接（他们仍然是simplexml对象）...

$results = $xml->xpath("//firstname"); 
foreach ($results as $result) { 
    echo $result->__toString(); 
}