Technote FL 17

January 1987

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}

In MPW C:

	err = Create("\pMyFile",0,myCreator,myType);
	CreateResFile("\pMyFile");
	err = ResError();

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}
	...

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*/

• * The File Manager
• * The Resource Manager
• * Technical Note M.FL.HFSRuminations

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