What to Watch Out for When Handling Negative Base Conversions with base_convert() in PHP

<span><span><span class="hljs-meta">&lt;?php</span></span><span> 
</span><span><span class="hljs-comment">// This section of code is unrelated to the article content and is only provided as a preliminary example</span></span><span> 
</span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"Starting PHP script execution...\n"</span></span><span>; 
</span><span><span class="hljs-meta">?&gt;</span></span><span> 
<p><hr></p>
<p></span><?php<br>
/*</p>
<ul>
<li>
<p>What to Watch Out for When Handling Negative Base Conversions with base_convert() in PHP</p>
</li>
<li></li>
<li>
<p>base_convert() is a built-in PHP function used to convert a number string between different bases.</p>
</li>
<li>
<p>Its function signature is: string base_convert(string $number, int $from_base, int $to_base)</p>
</li>
<li></li>
<li>
<p>However, in practice, base_convert() does not support directly handling negative numbers.</p>
</li>
<li>
<p>Below are several key points to keep in mind when dealing with negative numbers in base conversion.<br>
*/</p>
</li>
</ul>
<p>// 1. base_convert() does not support negative number input<br>
// The $number parameter accepted by base_convert() must be a string representation of a number, and it can only be a non-negative integer.<br>
// If you pass in a string with a minus sign (e.g., "-15"), the function treats the minus sign as an invalid character and ignores it, producing an incorrect result.</p>
<p>// Example<br>
$negativeNumber = "-15";<br>
$result = base_convert($negativeNumber, 10, 2);<br>
echo "Conversion result (input with minus sign): $result\n";<br>
// The output will ignore the minus sign, equivalent to converting "15", which is not the expected binary representation of a negative number.</p>
<p>// 2. Common approach to handling negative numbers<br>
// Since base_convert() does not support negative number conversion, the usual method is to first check the sign of the number,<br>
// then convert the absolute value, and finally manually add the minus sign back.</p>
<p>function base_convert_negative(string $number, int $from_base, int $to_base): string {<br>
$isNegative = false;<br>
if (strlen($number) > 0 && $number[0] === '-') {<br>
$isNegative = true;<br>
$number = substr($number, 1);<br>
}<br>
$converted = base_convert($number, $from_base, $to_base);<br>
return $isNegative ? '-' . $converted : $converted;<br>
}</p>
<p>// Test<br>
echo base_convert_negative("-15", 10, 2) . "\n";  // Output: -1111</p>
<p>// 3. Base conversion range limitations<br>
// base_convert() supports bases from 2 to 36.<br>
// Attempting to convert a base outside this range will return an empty string.<br>
// When handling negative numbers, ensure the bases provided are valid.</p>
<p>// 4. Representation of negative numbers in different bases<br>
// In some scenarios, you may want to represent a negative number in binary using two's complement.<br>
// However, base_convert() only performs straightforward numeric conversions and does not support two's complement or signed number representations.<br>
// If you require two's complement representation, you must implement bitwise operations and formatting yourself.</p>
<p>// 5. Summary<br>
// - base_convert() does not support directly converting numbers with a minus sign.<br>
// - You must manually separate the minus sign, convert the absolute value, and then reattach the minus sign.<br>
// - Bases must be between 2 and 36.<br>
// - Two's complement or other signed binary representations must be implemented manually.</p>
<p data-is-last-node="" data-is-only-node="">?><br>
</span>