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String Representations of File Paths

NSString provides a rich set of methods for manipulating strings as file-system paths. You can extract a path’s directory, filename, and extension, expand a tilde expression (such as “~me”) or create one for the user’s home directory, and clean up paths containing symbolic links, redundant slashes, and references to “.” (current directory) and “..” (parent directory).

Contents:

Representing a Path
User Directories
Path Components
File Name Completion

Representing a Path

NSString represents paths generically with ‘/’ as the path separator and ‘.’ as the extension separator. Methods that accept strings as path arguments convert these generic representations to the proper system-specific form as needed. On systems with an implicit root directory, absolute paths begin with a path separator or with a tilde expression (“~/...” or “~user/...”). Where a device must be specified, you can do that yourself—introducing a system dependency—or allow the string object to add a default device.

You can create a standardized representation of a path using stringByStandardizingPath. This performs a number of tasks including:

• Expansion of an initial tilde expression;

• Reduction of empty components and references to the current directory (“//” and “/./”) to single path separators;

• In absolute paths, resolution of references to the parent directory (“..”) to the real parent directory;

for example:

NSString *path;

NSString *standardizedPath;

path = @"/usr/bin/./grep";

standardizedPath = [path stringByStandardizingPath];

// standardizedPath: /usr/bin/grep

path = @"~me";

standardizedPath = [path stringByStandardizingPath];

// standardizedPath (assuming conventional naming scheme): /Users/Me

path = @"/usr/include/objc/..";

standardizedPath = [path stringByStandardizingPath];

// standardizedPath: /usr/include

path = @"/private/usr/include";

standardizedPath = [path stringByStandardizingPath];

// standardizedPath: /usr/include

User Directories

The following examples illustrate how you can use NSString’s path utilities and other Cocoa functions to get the user directories.

// assuming that users’ home directories are stored in /Users

NSString *meHome = [@"~me" stringByExpandingTildeInPath];

// meHome = @"/Users/me"

NSString *mePublic = [@"~me/Public" stringByExpandingTildeInPath];

// mePublic = @"/Users/me/Public"

You can find the home directory for the current user and for a given user with NSHomeDirectory and NSHomeDirectoryForUser respectively:

NSString *currentUserHomeDirectory = NSHomeDirectory();

NSString *meHomeDirectory = NSHomeDirectoryForUser(@"me");

Note that you should typically use the function NSSearchPathForDirectoriesInDomains to locate standard directories for the current user. For example, instead of:

NSString *documentsDirectory =

                [NSHomeDirectory() stringByAppendingPathComponent:@"Documents"];

you should use:

NSString *documentsDirectory;

NSArray *paths = NSSearchPathForDirectoriesInDomains

                    (NSDocumentDirectory, NSUserDomainMask, YES);

if ([paths count] > 0)  {

    documentsDirectory = [paths objectAtIndex:0];

}

Path Components

NSString provides a rich set of methods for manipulating strings as file-system paths, for example:

Using these and related methods described in NSString Class Reference, you can extract a path’s directory, filename, and extension, as illustrated by the following examples.

NSString *documentPath = @"~me/Public/Demo/readme.txt";

NSString *documentDirectory = [documentPath stringByDeletingLastPathComponent];

// documentDirectory = @"~me/Public/Demo"

NSString *documentFilename = [documentPath lastPathComponent];

// documentFilename = @"readme.txt"

NSString *documentExtension = [documentPath pathExtension];

// documentExtension = @"txt"

File Name Completion

You can find possible expansions of file names using completePathIntoString:caseSensitive:matchesIntoArray:filterTypes:. For example, given a directory ~/Demo that contains the following files:

ReadMe.txt readme.html readme.rtf recondite.txt test.txt

you can find all possible completions for the path ~/Demo/r as follows:

NSString *partialPath = @"~/Demo/r";

NSString *longestCompletion;

NSArray *outputArray;

unsigned allMatches = [partialPath completePathIntoString:&longestCompletion

    caseSensitive:NO

    matchesIntoArray:&outputArray

    filterTypes:NULL];

// allMatches = 3

// longestCompletion = @"~/Demo/re"

// outputArray = (@"~/Demo/readme.html", "~/Demo/readme.rtf", "~/Demo/recondite.txt")

You can find possible completions for the path ~/Demo/r that have an extension “.txt” or “.rtf” as follows:

NSArray *filterTypes = [NSArray arrayWithObjects:@"txt", @"rtf", nil];

unsigned textMatches = [partialPath completePathIntoString:&outputName

    caseSensitive:NO

    matchesIntoArray:&outputArray

    filterTypes:filterTypes];

// allMatches = 2

// longestCompletion = @"~/Demo/re"

// outputArray = (@"~/Demo/readme.rtf", @"~/Demo/recondite.txt")

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