Open resource file, specifying permission level

#include <Resources.h> Resource Manager

short OpenRFPerm( fileName, vRefNum, permission );

ConstStr255Param fileName ; address of length-prefixed filename

short vRefNum ; volume/directory reference number

short permission ; read/write permission code

OpenRFPerm can be used the first time a resource file is opened. It is

similar to OpenResFile except that it allows you to specify in which

volume/directory to find the file and you can set a file's read/write permission

fileName is the address of a Pascal-style length-prefixed filename identifying

the file containing the resources you want to access. It may contain a

vRefNum specifies the volume or directory reference number identifying

permission specifies the desired read/write permission code to be set for the

fsCurPerm 0 No change from existing file permission

fsRdPerm 1 Read only

fsWrPerm 2 Write only

fsRdWrPerm 3 Read and write

Returns: an integer; -1 indicates an error. Otherwise, it is the file

reference number which must be used in subsequent resource file

Notes: Inside Macintosh Volume 4, page 17 states that

OpenRFPerm, like OpenResFile, will not open the specified file twice;

it simply returns the reference number already assigned to the file. In

other words, OpenRFPerm cannot be used to open a second access path to a

This is not correct. Under MultiFinder, OpenRFPerm behaves exactly as

described if the application attempts to open a second path with write

access. That is, it returns a -1 and sets ResError to opWrErr (-49). But

OpenRFPerm will create multiple, unique, read-only access paths to a

resource file (under Finder or MultiFinder). This feature is not safe since

if a resource file is opened twice, once with read-write permission and

once with read-only permission, it is possible to get the resource maps in

OpenRFPerm behaves exactly as described if an application attempts to

open a second path, with write access, to a resource file without

MultiFinder. With MultiFinder, however, if the second attempt comes from a

different application than the first one, OpenRFPerm will not return the

reference number already assigned to the resource file, instead it will

return a -1 and ResError will be set to opWrErr (-49).