Zeus Tech Note
File Types, Creator Codes
and Extensions

What is a File Type and Why Do I Care?

There are many different types of files, such as application programs, documents and data files, or system utilities and drivers. A file's format must be known in order for a program or the OS to interpret it correctly. For example, a PICT file could not be read as if it were text by a word processor, but it might be recognized by a paint program. PCs and Macs have different conventions for indicating a file's format.

How do DOS/Windows use File Extensions?

Under DOS and Windows 3.1, file names are limited to eight characters, followed by a period (.) followed by a maximum of a 3-character extension. This extension is used to indicate the type of the file, although this is not universally reliable. For example, the ".TXT" extension indicates a text file. Windows 95 allows for longer filenames, but the three letter extension convention is still used heavily. Windows 95 files can also have a hidden file type, such as "htmlfile" which is similar to a Macintosh File Type (see below).

The associations between file extensions and applications are stored in the Windows WIN.INI file and the Windows Registry file. Refer to the TechNote, "Using Windows INI Files"

There are two main limitations to this system:

• A file must be named with a particular extension to be interpreted properly. Changing the name of the file will prevent it from working, in some cases.
  
  
• Any given file extension can only be associated with a single application. Thus, if you double-click on any TXT file, it will always be opened with the same application.

What are Macintosh File Types and Creator Codes?

Each Macintosh file contains a hidden File Type and Creator Code that indicate the file's format and the application that uses it, independent of the file's name. Every Macintosh application has a unique Creator Code. Apple maintains a registry of these Creator Codes to avoid conflicts between vendors. Most document formats have a unique File Type, but not always. Most notably. HTML files use the plain text type "TEXT" and are not identified as HTML files per se.

When you double-click a document, the Macintosh Finder searches for the application identified by the file's Creator Code. If it can't find the associated application, the Mac will list other applications that claim to recognize files of the specified File Type. An application interprets a document based on this File Type, such as "TEXT". (Applications all have a File Type of "APPL" which is analagous to the Windows .EXE extension, and tells the Finder that it is an executable).

An application may recognize more than one File Type. For example, deBabelizer can read many graphic file formats, each which have a unique File Type. You can open a document from within any application that understands that document's format, using the File menu's Open command.

Note that File Types and Creator Codes are always exactly four (4) characters and are case-sensitive. Some File Types and Creator Codes have trailing spaces to pad them out to four characters. You can view a file's File Type and Creator Code with several utilities, such as ResEdit or DropInfo.

There are two main advantages to this system:

• Files can be named freely without regard to their format, but Macintosh files are often named with an extension for convenience. For example web pages have an .HTM or .HTML extension.
  
  
• Documents of a given File Type do not all have to be associated with the same application. A TEXT file can be associated with either SimpleText or Microsoft Word, by virtue of the Creator Code.

• Files may lose their File Type and Creator Codes when transported over the internet or a network, especially when copied to/from non-Macintosh computers. Sometimes they are assigned generic or unknown File Types and Creator Codes, but these can be modified with ResEdit or DropInfo.
  
  
• To change the application with which a document is associated, you must change the document's Creator Code. For example, there is no easy way to force all TEXT files to be opened with a single word processor when they are double-clicked.

• File Types and Creator Codes are always exactly four (4) characters and are case-sensitive. Beware of trailing spaces, mistaking zeros for ohs, and special characters which are sometimes used for Creator Codes.
  
  
• Sometimes multiple applications will use the same Creator Code. For example, "ttxt" is used by both TeachText and SimpleText, "CARO" is used by both Adobe Acrobat Reader and Adobe Acrobat Exchange, and "StMl" is used by both Adobe PageMill and Adobe SiteMill.
  
  
• When an application is upgraded, the vendor may use the same Creator Code. Thus it is difficult to ensure that the latest version of software is opened automatically. Deleting extraneous versions of the software should help.
  
  
• HTML files use the "TEXT" File Type and do not have a unique file type unto themselves.

How do File Formats vary across platforms?

Some file formats are supported primarily on one of the two major platforms, whereas others are cross-platform. Some formats, such as PICT, TEXT and GIF can be read by numerous applications, while other formats are highly application-specific.

Note that many Macintosh applications will open files with a recognizable extensions. For example, Director for Macintosh can open DIR files with the File menu's Open command, even if the file's File Type is not set properly.

Some file extensions indicate that a file has been processed or encoded with one or more compression or encoding programs. These are generally used when transferring files via the internet.

How do I determine the File Type and Creator Code of a Macintosh File?

From the Finder, use ResEdit's Get Info command to inspect or change a file's Type and Creator. Other utilities, such as DropInfo provide the same capability.

From within Director, the FileIO Xtra's getFinderInfo method will return a file's File Type and Creator Code. Because a method can only return one thing, FileIO returns them both in one string, from which you can manually extract the Type and Creator. The first four characters are the Type and the last four characters are the Creator.

Warning: getFinderInfo seems to crash Director, so you may want to use the older FileIO XObject instead (see below)

When using the FileIO Xtra:

set fileXtra = new (Xtra "FileIO")

openFile (fileXtra, filename, mode)

set typeCreator = getFinderInfo (fileXtra)




set type = char 1 to 4 of typeCreator

set creator = char 5 to 8 of typeCreator

When using the FileIO XObject:

set fileObj = FileIO (mNew, fileName, mode)

set typeCreator = fileObj (mGetFinderInfo)




set type = char 1 to 4 of typeCreator

set creator = char 5 to 8 of typeCreator

What does a return value from getFinderInfo/mGetFinderInfo of "TEXT????" or "TEXT " indicate?

"TEXT" is the File Type and "???" is an unknown or missing Creator Code. Macintosh files that have been download or were transferred from a different platform may not have their Type and Creator set properly.

How do I set the File Type and Creator Code of a file?

From the Finder, use ResEdit's Get Info command to inspect or change a file's Type and Creator. Other utilities, such as DropInfo provide the same capability.

From within Director, the FileIO Xtra's setFinderInfo method will set a file's File Type and Creator Code. Note that the Type and Creator are passed within a single string, and a dummy character, such as a space is required between them. Note that this seems to crash on my 68K Mac!

When using the FileIO Xtra:

		set fileXtra = new (Xtra "FileIO")
		openFile (fileXtra, filename, mode)
		set type = "TEXT"
		set creator = "ttxt"
		setFinderInfo (fileXtra, type && creator)

When using the FileIO XObject, the Type and Creator are separate parameters:

		set fileObj = FileIO (mNew, filename, mode)
		set type = "TEXT"
		set creator = "ttxt"
		fileObj (mSetFinderInfo,type, creator)

Creator Codes for Common Applications:

Common File Types (alphabetical)

	AIF  - AIFF audio file, Mac and PC
	AVI  - Video for Windows Digital Video (Audio Video Interleaved)
	BMP  - Bitmap
	DCR  - Compressed Director Movie
	DDB  - Device-Dependent Bitmap. See BMP, DIB
	DIB  - Device Independent Bitmap. See BMP, DDB
	DIR  - Director movie
	DXR  - Protected Director movie
	EPS  - Encapsulated PostScript 
	FLC  - Animation sequence (from AutoCAD?)
	FLI  - Animation sequence (from AutoCAD?)
	GIF  - Graphics Interchange Format
	JPEG - Compressed PICTs
	JPG  - Compressed PICTs
	MOV  - QuickTime Digital Video
	PAL  - Palettes
	PCD  - Photo CD files 
	PCT  - PICT file
	PCX  - PaintBrush Files (PC)
	PIC  - PICT file
	PICT - PICT file
	PNT  - MacPanit format
	TIFF - Tagged Image File Format - popular for scanned photos
	WAV  - audio fiile. primarily PC, but also Mac
	WMF  - Windows Metafiles

Common File Types and their Applications:

Web Browser File Types

HTM, - Web browser, such as 
HTML - Netscape Navigator or 
"htmlfile" - Microsoft Internet Explorer 

URL - Internet Shortcut 

Business Applications File Types

xls - Microsoft Excel Spreadsheet 
"excel.sheet.5" - Microsoft Excel Spreadsheet 

Compression File Types

.zip  - IBM zip archive

.sit  - Mac stuffit archive

.gz   - GNUZip Compress (UNIX) (see GZIP for the Mac or WINZIP for Windows to decompress)

.hqx  - BinHex file (encoded for file transfers, must be decoded - Mac)

.z    - UNIX compressed file 

Image File Types

.GIF  - Graphics Interchange Format, a common web page format 
.JPG or JPEG - Joint Photographic Experts Group graphics file format, a common web page format 
.BMP  - Windows BitMaP picture file, Microsoft Paint, et al. 
.PICT - Macintosh PICTure format 

Sound File Types

	AIF or AIFF - Audio Interchange Format File
	au   - Audio file
	mid - Musical Interval Digital Interface format 
	wav - Wave file 

Word Processing File Types

DOC - Microsoft WordPad or Word 
TXT - Microsoft WordPad, NotePad or Write 
WRI - Microsoft WordPad, NotePad or Write 
W6BN" - Word Six Binary (I assume) Type 
"RTF " - Rich Text Format  (note trailing space in four-character File Type)
PDF - (Portable Document File format) Adobe Acrobat Reader 

Director 5 File Types and Creators

The files types that Director will import are:

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