Inside Macintosh: Files /

Chapter 2 - File Manager / File Manager Reference

File System Specification Routines / Opening Files

FSpOpenRF

You can use the FSpOpenRF function to open a file's resource fork.

FUNCTION FSpOpenRF (spec: FSSpec; permission: SignedByte;
                     VAR refNum: Integer): OSErr;

spec

An FSSpec record specifying the file whose resource fork is to be opened.

permission

A constant indicating the desired file access permissions.

refNum

A reference number of an access path to the file's resource fork.

DESCRIPTION

The FSpOpenRF function creates an access path to the resource fork of a file and returns, in the refNum parameter, an access path reference number to that fork. You can pass that reference number as a parameter to any of the low- or high-level file access routines.
The permission parameter should contain a constant indicating the desired file
access permissions.

SPECIAL CONSIDERATIONS

Generally, your application should use Resource Manager routines rather than File Manager routines to access a file's resource fork. The FSpOpenRF function does not read the resource map into memory and is generally useful only for applications (such as utilities that copy files) that need block-level access to a resource fork. In particular, you should not use the resource fork of a file to hold nonresource data. Many parts of the system software assume that a resource fork always contains resource data.

ASSEMBLY-LANGUAGE INFORMATION

The trap macro and routine selector for FSpOpenRF are

Trap macro	Selector
_HighLevelHFSDispatch	$0003

RESULT CODES

noErr	0	No error
nsvErr	-35	No such volume
ioErr	-36	I/O error
bdNamErr	-37	Bad filename
tmfoErr	-42	Too many files open
fnfErr	-43	File not found
opWrErr	-49	File already open for writing
permErr	-54	Attempt to open locked file for writing
dirNFErr	-120	Directory not found or incomplete pathname
afpAccessDenied	-5000	User does not have the correct access to the file