PHP实现内容页面的上一篇下一篇的功能的代码，$previous 为上一篇的id，$next_item 为下一篇的id。
$id_array = array();//获取该分类按指定排序得到的内容id数组
//获取上一篇，下一篇的id
if (is_array($id_array)) {
reset ($id_array);
$counter = 0;
foreach ($id_array as $key => $value) {
if ($value == (int)$_GET['products_id']) {
$position = $counter;
if ($key == 0) {
$previous = -1; // it was the first to be found
} else {
$previous = $id_array[$key - 1];
}
if (isset($id_array[$key + 1]) && $id_array[$key + 1]) {
$next_item = $id_array[$key + 1];
} else {
$next_item = $id_array[0];
}
}
$last = $value;
$counter++;
}
if ($previous == -1) $previous = $last;
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