在復雜的字符串處理場景中，可以靈活運用PHP的strpos函數來定位子字符串在字符串中的位置，并進一步進行處理。以下是一些示例用法：

1. 查找子字符串的位置：

$string = "Hello world";
$pos = strpos($string, "world");
echo "The position of 'world' in the string is: " . $pos;

2. 查找多個子字符串的位置：

$string = "Hello world, hello universe";
$keywords = array("world", "universe");
foreach ($keywords as $keyword) {
    $pos = strpos($string, $keyword);
    echo "The position of '$keyword' in the string is: " . $pos . "\n";
}

3. 判斷子字符串是否存在于字符串中：

$string = "Hello world";
$keyword = "world";
if (strpos($string, $keyword) !== false) {
    echo "The keyword '$keyword' exists in the string.";
} else {
    echo "The keyword '$keyword' does not exist in the string.";
}

4. 查找子字符串的位置并截取子字符串：

$string = "Hello world";
$keyword = "world";
$pos = strpos($string, $keyword);
if ($pos !== false) {
    $substring = substr($string, $pos);
    echo "The substring starting from '$keyword' is: " . $substring;
} else {
    echo "The keyword '$keyword' does not exist in the string.";
}

通過靈活運用strpos函數，可以更方便地處理復雜的字符串場景，并實現所需的邏輯功能。