CreateResFile
CreateResFile checks to see if a resource file with a given name exists,
and if it does, returns a dupFNErr (-48) error. Unfortunately, to do this check,
CreateResFile uses a call that follows the Poor Man's Search Path (PMSP).
CreateResFile checks to see if a resource file with a given name exists, and if
it does, returns a dupFNErr (-48) error. Unfortunately, to do the check, CreateResFile
calls PBOpenRF, which uses the Poor Man's Search Path (PMSP). For example, if we have a
resource file in the System folder named `MyFile' (and no file with that name in the
current directory) and we call CreateResFile('MyFile'), ResError will return
a dupFNErr, since PBOpenRF will search the current directory first, then
search the blessed folder on the same volume. This makes it impossible to use
CreateResFile to create the resource file 'MyFile'
in the current directory if a file with the same name already exists
in a directory that's in the PMSP.
To make sure that CreateResFile will create a resource file in the
current directory whether or not a resource file with the same name already
exists further down the PMSP, call _Create (PBCreate or
Create) before calling CreateResFile:
err := Create('MyFile',0,myCreator,myType);
{0 for VRefNum means current volume/directory}
CreateResFile('MyFile');
err := ResError; {check for error}
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In MPW C:
err = Create("\pMyFile",0,myCreator,myType);
CreateResFile("\pMyFile");
err = ResError();
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This works because _Create does not use the PMSP. If we already
have `MyFile' in the current directory, _Create will fail
with a dupFNErr, then, if `MyFile' has an empty resource
fork, CreateResFile will write a resource map, otherwise,
CreateResFile will return dupFNErr. If there is no file named
'MyFile' in the current directory, _Create will create one
and then CreateResFile will write the resource map.
Notice that we are intentionally ignoring the error from _Create,
since we are calling it only to assure that a file named `MyFile' does
exist in the current directory.
Please note that SFPutFile does not use the PMSP, but that
FSDelete does. SFPutFile returns the vRefNum/WDRefNum
of the volume/folder that the user selected. If your program deletes a resource
file before creating one with the same name based on information returned from
SFPutFile, you can use the following strategy to avoid deleting the
wrong file, that is, a file that is not in the directory specified by the
vRefNum/WDRefNum returned by SFPutFile, but in some
other directory in the PMSP:
VAR
wher : Point;
reply : SFReply;
err : OSErr;
oldVol : Integer;
...
wher.h := 80; wher.v := 90;
SFPutFile(wher,'','',NIL,reply);
IF reply.good THEN BEGIN
err := GetVol(NIL,oldVol); {So we can restore it later}
err := SetVol(NIL,reply.vRefNum);{for the CreateResFile call}
{Now for the Create/CreateResFile calls to create a resource file that
we know is in the current directory}
err := Create(reply.fName,reply.vRefNum,myCreator,myType);
CreateResFile(reply.fName); {we'll use the ResError from this ...}
CASE ResError OF
noErr:{the create succeeded, go ahead and work with the new
resource file -- NOTE: at this point, we don't know what's
in the data fork of the file!!} ;
dupFNErr: BEGIN {duplicate file name error}
{the file already existed, so, let's delete it. We're
now sure that we're deleting the file in the current directory}
err:= FSDelete(reply.fName,reply.vRefNum);
{now that we've deleted the file, let's create the new one,
again, we know this will be in the current directory}
err:= Create(reply.fName,reply.vRefNum,myCreator,myType);
CreateResFile(reply.fName);
END; {CASE dupFNErr}
OTHERWISE {handle other errors} ;
END; {Case ResError}
err := SetVol(NIL,oldVol);{restore the default directory}
END; {If reply.good}
...
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In MPW C:
Point wher;
SFReply reply;
OSErr err;
short oldVol;
wher.h = 80; wher.v = 90;
SFPutFile(wher,"","",nil,&reply);
if (reply.good )
{
err = GetVol(nil,&oldVol); /*So we can restore it later*/
err = SetVol(nil,reply.vRefNum);/*for the CreateResFile call*/
/*Now for the Create/CreateResFile calls to create a resource
file that we know is in the current directory*/
err = Create(&reply.fName,reply.vRefNum,myCreator,myType);
CreateResFile(&reply.fName); /*we'll use the ResError
from this ...*/
switch (ResError())
{
case noErr:;/*the create succeeded, go ahead and work with the
new resource file -- NOTE: at this point, we don't know what's
in the data fork of the file!!*/
break; /* case noErr*/
case dupFNErr: /*duplicate file name error*/
/*the file already existed, so, let's delete it.
We're now sure that we're deleting the file in the
current directory*/
err= FSDelete(&reply.fName,reply.vRefNum);
/*now that we've deleted the file, let's create the new one,
again, we know this will be in the current directory*/
err= Create(&reply.fName,reply.vRefNum,
myCreator,myType);
CreateResFile(&reply.fName);
break; /*case dupFNErr*/
default:; /*handle other errors*/
} /* switch */
err = SetVol(nil,oldVol);/*restore the default directory*/
} /*if reply.good*/
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Note:
OpenResFile uses the PMSP too, so you may have to adopt
similar strategies to make sure that you are opening the desired resource file
and not some other file further down the PMSP. This is normally not a problem
if you use SFGetFile, since SFGetFile does not use the PMSP,
in fact, SFGetFile does not open or close files, so it doesn't run
into this problem.
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References
The File Manager
The Resource Manager
Technical Note M.FL.HFSRuminations
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