What does __FILE__ mean?

问题:

I have the following code from Codeigniter index.php

My understanding is that,

If / of string position in $system_folder (in this case CIcore_1_7_1) is false, and if realpath function exists AND (?) is not false, $system_folder is assigned to (?) /$system_folder. else $system_folder is assigned to $system_folder with replacing \\ with /.

Q1. What does realpath function means?

Q2. What does this mean?

@realpath(dirname(__FILE__))

Q3. Am I right? Do I have any misunderstanding?

Q4. What kind of situation do you need the following?

str_replace("\\", "/", $system_folder)

---

$system_folder = "CIcore_1_7_1";

/*
|---------------------------------------------------------------
| SET THE SERVER PATH
|---------------------------------------------------------------
|
| Let's attempt to determine the full-server path to the "system"
| folder in order to reduce the possibility of path problems.
| Note: We only attempt this if the user hasn't specified a 
| full server path.
|
*/

if (strpos($system_folder, '/') === FALSE)
{
    if (function_exists('realpath') AND @realpath(dirname(__FILE__)) !== FALSE)
    {
        $system_folder = realpath(dirname(__FILE__)).'/'.$system_folder;
    }
}
else
{
    // Swap directory separators to Unix style for consistency
    $system_folder = str_replace("\\", "/", $system_folder); 
}

回答1:

1. The realpath() function gives you the file-system path, with any symbolic links and directory traversing (e.g. ../../) resolved. The dirname() function gives you just the directory, not the file within it.

2. __FILE__ is a magic constant that gives you the filesystem path to the current .php file (the one that __FILE__ is in, not the one it's included by if it's an include.

3. Sounds about right.

4. This is to translate from Windows style (\) paths to Unix style (/).

回答2:

__FILE__ is simply the name of the current file. realpath(dirname(__FILE__)) gets the name of the directory that the file is in -- in essence, the directory that the app is installed in. And @ is PHP's extremely silly way of suppressing errors.

回答3:

__FILE__

The full path and filename of the file. If used inside an include, the name of the included file is returned. Since PHP 4.0.2, FILE always contains an absolute path with symlinks resolved whereas in older versions it contained relative path under some circumstances.

---

string dirname  ( string $path  )

Given a string containing a path to a file, this function will return the name of the directory.

---

str_replace("\\", "/", $system_folder)

You need this to be consisten in path separators between different operating systems. Windows uses \ and *nix uses /, you keep with /.