Changes

A key element of gaining proficiency in any programming language involves the ability to work with files and file systems. The level of difficulty in working with files various varies from very easy to hard, depending on the programming language concerned. The C programming language, on which Objective-C is based, tended to make file handling a little hard relative to the standards of today's programmer friendly object oriented languages. The good news for Objective-C developers is that the Foundation Framework includes a number of classes designed specifically to make the task of working with files and directories as straightforward as possible.

* '''NSData''' - The ''NSData'' class provides a useful storage buffer into which the contents of a file may be read, or from a which data may be written to a file.

When using the above classes, pathnames are defined using the UNIX convention. As such each component of a path is separated by a forward slash (/). Paths that do not begin with a slash are interpreted to be relative to a current working directory. For example, if the current working directory is ''/home/objc'' and the path name is ''myapp/example.m'' then the file is considered to have a full pathname of ''/home/objc/myapp/example.m''.

In addition, the home directory of the current user can be represented using the tilde (~) character. For example the pathname ''~/example.m'' references a file named ''example.m'' located in the home directory of the current user. the The home directory of another user may be reference referenced by prefixing the user name with a ~. For example, ''~john/demo.m'' references a file located in the home directory of a user named ''john''.

In the above example we have declared a variable named ''filemgr''to point to an object of type NSFileManager, and then created an object of that type using the NSFileManager ''defaultManager'' class methods method and assigned it to the variable. Having created the object we can begin to use it to work with files and directories.

The current working directory may be identified using the ''currentDirectoryPath'' instance method of our NSFileManager object. The current path is returned from the method in the form of a an NSString object:

The current working directory of a running Objective-C program can be changed with a call to the ''changeCurrentDirectoryPath'' method. The destination directory path is passed as an argument to the instance method in the form of an NSString object. Note that this methods method returns a boolean ''YES'' or ''NO'' result to indicate if the requested directory change was successful for not:

A new directory is created using the ''createDirectoryAtPath'' instance method, once again passing through the pathname of the new directory as an argument and returning a boolean success or failure result. This method also takes an additional arguments argument in the form a set of attributes for the new directory. Specifying ''nil'' will use the default attributes:

An existing directory may be moved (also known as renaming) using the ''movePath'' method. This methods method takes the source and destination pathnames as arguments and requires that the destination directory not already exist. If the target directory exists, a boolean NO result is returned by the method to indicate failure of the operation:

A listing of the files contained within a specified directory can be obtained using the ''directoryContentsAtpath'' method. This methods method takes the directory pathname as an argument and returns an NSArray object containing the names of the files in that directory:

When executed on a Mac OS X system, we can expect to see the following output (note that ''/tmp'' on a Mac OS X system is a symbolic link to ''private/tmp''):