N ways to get file extension in PHP

N ways to get file extensions in PHP
Collected from the Internet, basically the following methods:


The first method:
function get_extension($file)
{
substr(strrchr($file , '.'), 1);
}
The second method:
function get_extension($file)
{
return substr($file, strrpos($file, '.')+1);
}
th 3 methods:
function get_extension($file)
{
return end(explode('.', $file));
}
Fourth method:
function get_extension($file)
{
$info = pathinfo ($file);
return $info['extension'];
}
The fifth method:
function get_extension($file)
{
return pathinfo($file, PATHINFO_EXTENSION);
}
The above methods are rough After looking at it, it seems that they all work, especially methods 1 and 2, which I have been using before I didn't know that pathinfo has a second parameter. But if you think about it carefully, the first four methods have various shortcomings. To obtain the file extension completely correctly, you must be able to handle the following three special situations.
No file extension
The path contains the characters ., such as /home/test.d/test.txt
The path contains the characters ., but the file has no extension. For example, /home/test.d/test
It is obvious: 1 and 2 cannot handle the third situation, and 3 cannot correctly handle the first and third situations. 4 is handled correctly, but when the extension is not present, a warning is issued. Only method 5 is the most correct method. By the way, take a look at the pathinfo method. The introduction on the official website is as follows:
$file_path = pathinfo('/www/htdocs/your_image.jpg');

echo "$file_path ['dirname']n";
echo "$file_path ['basename']n";
echo "$file_path ['extension']n";
echo "$file_path ['filename']n"; // only in PHP 5.2+
It will return an array containing up to four elements, but it will not There are always four. For example, if there is no extension, there will be no extension element, so the warning will be found in the fourth method. But phpinfo also supports the second parameter. You can pass a constant to specify a certain part of the data to be returned:
PATHINFO_DIRNAME - directory
PATHINFO_BASENAME - file name (including extension)
PATHINFO_EXTENSION - extension
PATHINFO_FILENAME - file name (excluding extension, PHP>5.2)
These four The values ​​of the constants are 1, 2, 4, and 8. At first, I thought I could specify multiple ones through the OR operation:
pathinfo($file, PATHINFO_EXTENSION | PATHINFO_FILENAME);
Later I found out that this doesn’t work, and it will only return several sequences. or the smallest of the arithmetic constants. That is, the smallest bit among the four flag bits is a constant of 1.