How to get the file name extension in PHP

$str = ' AS.DA.EFG ';   
Gets the file suffix name   
//strrchr-The last occurrence of the specified character in the string   
, Echo substr (STRRCHR ($str, "."), 1). " <br/> ";   
       
       
Strrpos-calculates the position of the specified string last occurrence in the destination string   
echo substr ($str, Strrpos ($str, ".") +1). " <br/> ";   
       
       
End-the internal pointer of the array to the last cell   
, Echo End (Explode ('. ', $str)). " <br/> ";   
       
       
Pathinfo-returns the information of the file path   
$file = PathInfo ($STR);   
echo $file [' extension ']. <br/> ";   
       
Echo PathInfo ($str, pathinfo_extension). " <br/> ";

The above several ways coarse look, seems to be all right, especially 1, 2 kinds of methods, before I do not know PathInfo has the second parameter has been used. But think about it, the first four methods have all kinds of problems. To get the file extensions exactly right, you must be able to handle the following three special cases.

No file name extension

The path contains characters. such as/home/test.d/test.txt

The path contains characters., but the file does not have an extension. such as/home/test.d/test

Obviously: 1, 2 can not deal with the third situation, 3 can not correctly deal with the 13th case. 4 can be handled correctly, but a warning is issued when no extension exists. Only the 5th method is the right approach. By the way, look at the PathInfo method. The official website introduces 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 returns an array containing up to four elements, but does not always have four, for example, without an extension, there will be no extension element, so the 4th method will find the warning. But Phpinfo also supports the second parameter. You can pass a constant that specifies the data to return a part of:

Pathinfo_dirname-Table of Contents

Pathinfo_basename-file name (including extension)

Pathinfo_extension-name extension

Pathinfo_filename-filename (without extension, php>5.2)

The values for these four constants are 1, 2, 4, 8, and at first I thought you could specify multiple by or operation:

PathInfo ($file, Pathinfo_extension | Pathinfo_filename);

It turns out that this is not going to work, and that only returns a few of the ones that are the smallest of the constants or operands. That is, a constant with a minimum of 1 digits in four flags.

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