从SQL数据库生成XML文件时持续报文档为空错误，求排查

Let's walk through the issues in your code that are causing this error and invalid XML output:

1. Broken parseToXML Function #

Your string replacement logic has two critical flaws:

• Every replacement uses the original $htmlStr instead of building on the modified $xmlStr, so only the last replacement (& → &) actually takes effect.
• The single-quote replacement line has a syntax error: ''$htmlStr is invalid PHP syntax, which will throw an error and halt your script entirely (leading to the empty document message).

Fixed function:

function parseToXML($htmlStr) { 
    $xmlStr = $htmlStr;
    $xmlStr = str_replace('<','&lt;',$xmlStr); 
    $xmlStr = str_replace('>','&gt;',$xmlStr); 
    $xmlStr = str_replace('"','&quot;',$xmlStr); 
    $xmlStr = str_replace("'",'&#39;',$xmlStr); 
    $xmlStr = str_replace("&",'&amp;',$xmlStr); 
    return $xmlStr; 
}

2. Invalid Output Breaking XML Structure #

You're outputting non-XML content before and within your XML document:

• echo "test1 \n\n"; and other test outputs come before the XML declaration <?xml version='1.0' ?>, which violates XML rules (the declaration must be the first line of the document).
• The <br> tags and raw row content in your first loop are plain HTML/text that doesn't belong in an XML file—this will make the document invalid even if it loads.

Fix: Remove all debug echo statements (test1/test2/test3) and the first loop that outputs <br> tags.

3. Result Set Exhausted Before XML Nodes Are Generated #

Your first while($row = mysqli_fetch_assoc($result)) loop reads all rows from the result set, so when you try to loop again later to generate <marker> nodes, there are no rows left to fetch.

Fix: Delete the first loop entirely (it's just debug output anyway) so the result set is intact for generating your XML nodes.

4. Potential Header Issues from config.php #

Even if you placed the header() call at the top, if config.php outputs any content (like whitespace, echo statements, or a UTF-8 BOM), PHP will send headers automatically before your header() call, which can break the XML content type and cause silent failures.

Fix: Check config.php to ensure it has no output (no leading/trailing spaces, no echo statements) and is saved as UTF-8 without BOM.

Full Corrected Code #

<?php 
header('Content-type: text/xml'); 
require("config.php"); 

function parseToXML($htmlStr) { 
    $xmlStr = $htmlStr;
    $xmlStr = str_replace('<','&lt;',$xmlStr); 
    $xmlStr = str_replace('>','&gt;',$xmlStr); 
    $xmlStr = str_replace('"','&quot;',$xmlStr); 
    $xmlStr = str_replace("'",'&#39;',$xmlStr); 
    $xmlStr = str_replace("&",'&amp;',$xmlStr); 
    return $xmlStr; 
} 

$sql = "SELECT * FROM markers;"; 
$result = mysqli_query($connection, $sql); 

// Start XML document
echo "<?xml version='1.0' ?>"; 
echo '<markers>'; 

if(mysqli_num_rows($result) > 0) { 
    while($row = mysqli_fetch_assoc($result)){ 
        echo '<marker '; 
        echo 'id="' . $row['id'] . '" '; 
        echo 'name="' . parseToXML($row['name']) . '" '; 
        echo 'address="' . parseToXML($row['address']) . '" '; 
        echo 'lat="' . parseToXML($row['lat']) . '" '; 
        echo 'lng="' . parseToXML($row['lng']) . '" '; 
        echo 'type="' . parseToXML($row['type']) . '" '; 
        echo '/>'; 
    } 
} 

echo '</markers>'; 
?>

内容的提问来源于stack exchange，提问作者Ryan Brown