Five ways PHP Gets the file name extension

This is a written question I encountered when I applied for an internship:

Use more than five ways to get the extension of a file.

Requirements: dir/upload.image.jpg, find. jpg or JPG,

Must be handled using PHP's own processing function, which cannot be significantly duplicated and can be encapsulated into functions such as GET_EXT1 ($file _name), get_ext2 ($file _name)

The following is my reference to the online summary of the five methods, are relatively simple, words not much to say, directly on the code:

Method 1:

function GetExt1 ($filename)

{

$arr = Explode ('. ', $filename);

Return Array_pop ($arr);;

}

Method 2:

function GetExt2 ($filename)

{

$ext = STRRCHR ($filename, '. ');

return $ext;

}

Method 3:

function GetExt3 ($filename)

{

$pos = Strrpos ($filename, '. ');

$ext = substr ($filename, $pos);

return $ext;

}

Method 4:

function GetExt4 ($filename)

{

$arr = PathInfo ($filename);

$ext = $arr [' extension '];

return $ext;

}

Method 5:

function GetExt5 ($filename)

{

$str = Strrev ($filename);

Return Strrev (STRCHR ($str, '. ', true));

}

Five ways PHP Gets the file name extension