Drupal 7 Module Development

Working with Files and Images
File API
In Drupal 6, most file handling functionality was provided through a rough core API
combined with contributed modules such as Filefield. Drupal 7 provides a more
robust and consistent API that allows developers to interact with files in a standard
set of functions that perform tasks like creating, opening, moving, and deleting files.
In order for files to be associated with nodes and other Drupal content, they must
have a record in Drupal's file table. Each record identifies a file with a unique ID
as well as associated metadata like file size and mime-type.
Many File API functions, such as file_copy() and file_move(), take a file object
as one of their arguments. The file object is a PHP standard class containing the
metadata from the files table, and these API functions manage updating the
information in the files table when files are moved or deleted. This is one reason
it is so important to use these API functions for files associated with content—if you
don't, the files table will be inconsistent and your files may not show up properly.
If you need to work with files outside the context of Drupal content, there is
a separate set of functions in the File API with unmanaged in their name. For
instance, where file_copy() will update the files table and copy your file,
file_unmanaged_copy() will just copy the file.
For a full list of the functions available in the File API,
refer to the API documentation at:
http://api.drupal.org/api/group/file/7
Here is a simple example of how this works. A common task while building a
Drupal site is importing data from another source and turning it into nodes. This
will not only include textual information like the title and body, but also images.
These images may live in a local directory, or they may live out on a website you're
importing from.
Let's look at how we can grab a file from an external site, save it to the default file
system, and attach it to a node we create. For this example, you will be working with
the field image in the article content type.
First we need to get a file and save it:
$image = file_get_contents('http://drupal.org/files/issues/druplicon_
2.png');
$file = file_save_data($image, 'public://druplicon.png',FILE_EXISTS_
REPLACE);
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