// Other variables
$MAX_FILENAME_LENGTH = 260;
$file_name = $_FILES[$upload_name]['name'];
//echo "testing-".$file_name."<br>";
//$file_name = strtolower($file_name);
$file_extension = end(explode('.', $file_name)); //ERROR ON THIS LINE
$uploadErrors = array(
0=>'There is no error, the file uploaded with success',
1=>'The uploaded file exceeds the upload max filesize allowed.',
2=>'The uploaded file exceeds the MAX_FILE_SIZE directive that was specified in the HTML form',
3=>'The uploaded file was only partially uploaded',
4=>'No file was uploaded',
6=>'Missing a temporary folder'
);
什么好主意吗?过了2天，还是卡住了。
由于它在超过10年的时间里升起了一个旗帜，但工作得很好，并返回预期的值，一个小stfu操作符是你都在寻找的最好的坏习惯:
$file_extension = @end(explode('.', $file_name));
但是警告，不要在循环中使用，因为会影响性能。
最新版本的php 7.3+提供了array_key_last()和array_key_first()方法。
https://www.php.net/manual/en/function.array-key-last.php
uuuuuuu
uu$$$$$$$$$$$uu
uu$$$$$$$$$$$$$$$$$uu
u$$$$$$$$$$$$$$$$$$$$$u
u$$$$$$$$$$$$$$$$$$$$$$$u
u$$$$$$$$$$$$$$$$$$$$$$$$$u
u$$$$$$$$$$$$$$$$$$$$$$$$$u
u$$$$$$" "$$$" "$$$$$$u
"$$$$" u$u $$$$"
$$$u u$u u$$$
$$$u u$$$u u$$$
"$$$$uu$$$ $$$uu$$$$"
"$$$$$$$" "$$$$$$$"
u$$$$$$$u$$$$$$$u
u$"$"$"$"$"$"$u
uuu $$u$ $ $ $ $u$$ uuu
u$$$$ $$$$$u$u$u$$$ u$$$$
$$$$$uu "$$$$$$$$$" uu$$$$$$
u$$$$$$$$$$$uu """"" uuuu$$$$$$$$$$
$$$$"""$$$$$$$$$$uuu uu$$$$$$$$$"""$$$"
""" ""$$$$$$$$$$$uu ""$"""
uuuu ""$$$$$$$$$$uuu
u$$$uuu$$$$$$$$$uu ""$$$$$$$$$$$uuu$$$
$$$$$$$$$$"""" ""$$$$$$$$$$$"
"$$$$$" ""$$$$""
$$$" $$$$"
PHP抱怨是因为end()期望对它想要更改的内容(只能是变量)的引用。但是，您可以直接将爆炸()的结果传递给end()，而不需要先将其保存到变量中。当explosion()返回您的值时，它只存在于内存中，没有变量指向它。不能创建对不存在的东西(或内存中未知的东西)的引用。
或者换句话说:PHP不知道你给他的值是直接的值还是指向值的指针(指针也是一个变量(整数)，它存储了内存的偏移量，也就是实际值所在的位置)。PHP希望这里总是有一个指针(引用)。
但是因为这在PHP 7中仍然只是一个通知(甚至没有被弃用)，你可以保存忽略通知并使用忽略操作符，而不是完全取消激活通知的错误报告:
$file_extension = @end(explode('.', $file_name));
