Identifying Files, Directories, and Volumes
- New Special-Purpose Features in the File Manager
- A Simpler Safe-Save Strategy
- Using the File Manager
- Limitations on MFS Disks
Identifying Files, Directories, and Volumes Updated methods
Your application typically specifies a filename and location when it calls the
File Manager to open or delete a file. It typically receives filenames and
user interface for creating, saving, opening, and removing files.
File System Specifications
Conventions for identifying files, directories, and volumes have evolved as the
File Manager has matured. Version 7.0 introduces a simple, standard form
for identifying a file or directory, called a file system specification. You can
use a file system specification whenever you must identify a file or directory
The file system specification contains
• the volume reference number of the volume on which the file or
directory resides
• the directory ID of the parent directory
• the name of the file or directory
For a complete description of the new data structure, the file system
The Finder in version 7.0 uses alias records, which are resolved into FSSpec
records, to identify files to be opened or printed. (The description of required
file information to your application and how your application retrieves it.)
FSSpec record for a file or directory. For a complete description of
File Specification Strategies
The original Macintosh File System (MFS) is a flat file system-that is, a
system in which all files are stored at the same level on a volume (the volume
is not subdivided into directories). To uniquely identify a file, you need to
specify only a volume and a filename. In high-level MFS functions, you pass
In MFS, you can specify a file in either of two ways:
• a full pathname, which contains the names of both the volume and the
file, in the fileName parameter
• filename by name in the fileName parameter and volume by volume
reference number, a unique number assigned when the volume is
The following figure illustrates the two ways to identify a file in MFS.
To improve performance, especially with larger volumes, Apple Computer,
Inc., introduced the Hierarchical File System (HFS) on the Macintosh Plus
computer and later models. In HFS, a volume can be divided into smaller units
known as directories, which can themselves contain files or other
directories. Each file on an HFS volume is stored in a directory. To identify a
file in HFS, you must specify its volume, its parent directory, and its name.
system software assigns each directory a name. The Hierarchical File System
File Manager routines include an additional parameter, the dirID
parameter, to handle the directory specification.
In HFS, each folder created by the user is a directory. The folders represent a
true hierarchy in the file system. In MFS, folders are an illusion maintained
for the user by the system software. The first-level directory on a volume,
the one that contains all of the other directories, is known as the root
directory.
For compatibility between HFS and MFS, Apple introduced the concept of
working directories. A working directory is a combined directory and
volume specification. To make a directory into a working directory, the
File Manager establishes a control block that contains both the volume and
unique working directory reference number, which you can use to identify the
directory. You can use the working directory reference number in place of a
volume specification in all of the MFS functions.
Note: Working directories were introduced solely for
compatibility between HFS and MFS. If you are writing an application
to run in system software version 7.0, you do not need to use
working directories.
In summary, HFS recognizes three kinds of file system objects: files,
directories, and volumes. You can identify them using these labels:
File filename
Directory directory name
directory ID
Working directory reference number,
which also implies a volume
Volume volume name
volume reference number
working directory reference number,
which also implies a directory
In HFS, you can pass a complete file specification in any of four ways:
• full pathname
• volume reference number and partial pathname
• working directory reference number and partial pathname
• volume reference number, directory ID, and partial pathname
A full pathname consists of the name of the volume, the names of all
directories between the root directory and the target, and the name of the
target. A full pathname starts with a character other than a colon and contains
at least one colon. If the first character is a colon, or if the pathname contains
no colons, it is a partial pathname. If a partial pathname starts with the name
of a parent directory, the first character in the pathname must be a colon. If a
partial pathname contains only the name of the target file or directory, the
leading colon is optional.
number or drive number, but volume reference number is preferred. A value
of 0 represents the default volume. A volume name in the pathname overrides
any other volume specification. Unlike a volume name, a volume reference
number is guaranteed to be unique. It changes, however, each time a volume is
mounted.
Note: The system software that accompanied the release of HFS
introduced the PBHSetVol function for setting the default volume on
a hierarchical disk. Do not use the PBHSetVol function or the
development environments. If you need to set the default volume, use
A working directory reference number represents both the directory ID and
the volume reference number. If you specify any value other than 0 for the
dirID parameter, that value overrides the directory ID implied by a working
directory reference number in the volume parameter. The volume
specification remains valid.
The four ways to identify a file in HFS are illustrated in the following figure.
Specifications," replaces both the MFS and the HFS conventions for identifying
files and directories in most cases. In system software version 7.0, you use
the historical forms primarily when you are calling low-level File Manager
functions.