TweetFollow Us on Twitter

Vol Search XFCN
Volume Number:7
Issue Number:6
Column Tag:HyperChat

Related Info: File Manager

HFS Volume Search XFCN

By Mark Armstrong, Pharos Technologies

Note: Source code files accompanying article are located on MacTech CD-ROM or source code disks.

The SearchVol XFCN

The SearchVol XFCN searches the specified volume and returns the full path name of the file. This is extremely useful if you want to launch a document from within Hypercard but you are not sure where the file is located on the volume. SearchVol will return the full pathname of the file which you can then pass directly to the Hypertalk open command.

SearchVol uses a recursive algorithm to walk through the hierarchical file structure looking for a match. If it finds a match, it constructs the full path name by walking back up the tree. Once it has the full path name, it returns it to Hypercard. If no match is found, the XFCN will return empty. See the Other Issues section of this article for further discussion of the recursive nature of the algorithm.

SearchVol searches in the specified volume, or, if no volume is specified, in the system volume. Since PBGetVInfo prefers to have the volume specified in the form “volname:” (and since I am in the unfortunate habit of just passing “volume” without the trailing colon,) we simply check to see if there is a trailing colon on the specified volume name. If there is not, we add one.

Once we have the volume reference numbers we can begin the search. We start by determining the number of files and directories in the root directory by calling PBGetCatInfo and then we make the initial call to SearchFile, which is the real guts of the XFCN.

The Search Engine

The SearchFile function is very similar to Clifford Story’s walktree function in the October ’88 MacTutor (Programmer’s Workshop; HFS Transfer DA) Cliff wrote his in Pascal - this one is in C. But the structure of the routines is quite similar. For the gospel on searching HFS volumes, refer to Apple’s Technical Note 68.

You will notice that SearchFile consists of two for loops. The first for loop is looking for files. We look for file by accepting only the cases in which bit 4 of ioFlAttrib is not set. The second for loop is looking strictly for directories. If it is a file, then we check to see if there is a match. If it is a directory, then we look inside that directory with a recursive call to search file.

So, why the two for loops? Well, I wanted the routine to be equivalently fast for any file in a given directory. With just a single for loop, a file in the route directory named “AAAA” would most likely be found very quickly. Where as, a file named “ZZZZ” would take much longer, assuming, of course, that the volume in question was an average user’s 40 meg hard disk. Consequently, if we look through all the files first for a given directory before diving down to the next level in the hierarchy, we should be able to get a more consistent search time for files at the same hierarchical level. Once the recursive searching is complete, we check to see if a file was found. If a file was not found, fErr will contain fnfErr. On the other hand, if a file was found then we need to walk back up the hierarchy to construct the full path name that Hypercard requires for its file commands such as open, read, and print. We build the path name in the returnValue handle so it is available when we return to Hypercard.

Error Handling

In the SearchVol XFCN listed below I have included only a skeletal version of the required error handling. I have done this so as not to cloud the concepts on which I am trying to focus. However, I do have a few words about error handling that I would like to share.

There is an interesting catch-22 situation that arises for the author of external functions. The situation is this. If Hypercard is expecting you to return a value from an external function, then Hypercard needs a way to determine if the returned value is an error string or the expected result. In many XFCN’s available today, it is difficult (if not impossible) to determine in the general case if the string returned from the external is an error or not. As an example, suppose there is an XFCN that returns a file name. Furthermore, lets say that in case of error, the XFCN returns the error number. Now lets say that the XFCn is called from Hypertalk and the returned result is “-43”. Is this an error code for file not found or is it just a file that happens to be named “-43”. To avoid these problematic circumstances, the XFCN designer must make it very easy for the Hypertalk programmer to ascertain:

1) If an error occurred

2) What was the nature of the error

Another common approach is to return empty if an error occurred. Unfortunately, empty does not tell the Hypertalk programmer (to say nothing of the user) what went wrong. Consequently, it is difficult to take appropriate action.

Some programmers have circumnavigated the problem by forcing the declaration of a global variable. If an error occurs, then the global variable is set to notify Hypertalk that things did not go as planned. This method works has its advantages, but it can be an extra hassle if the Hypertalk programmer does not know he is required to declare the global. Whatever you decide to do, make your error checking rigorous and complete. Everyone will benefit.

Other Issues

SearchVol, as it is, is a foundation on which one can build. For example, one could easily search all mounted volumes by creating an outside loop that walked through the volume queue. For example:

/* 1 */

QHdrPtr QQ;
VCB     *Cur;

QQ = GetVCBQHdr();
Cur = (VCB *)(QQ->qHead);
   
do {
   /* Use Cur->vcbVN as the current volName */
   /* Put search volume code here */
   Cur = (VCB *)(Cur)->qLink;
   } while (Cur != 0L);

Another possibility is to extend the XFCN so that it returns all occurrences of the specified file - rather than just the first occurrence. In such a case, you would not return after finding a file but would simply store the full pathname of the file and then continue the search down the hierarchy. In this way, you could duplicate in Hypercard the functionality of the Find File desk accessory.

Other ideas include filtering out files by type or modification date, cataloging subdirectories on a volume, and the list goes on.

Finally, it is important to discuss the advantages and limitations of using a recursive algorithm for hierarchical searching. The advantages are that the code is small and simple. The primary limitation is that the stack grows with each recursive call. On a large hard disk or CD-ROM this could be a problem. I have used the recursive algorithm as a demonstration of recursive methods in an ideal world. Reality dictates that machines have a finite amount of memory. It is more prudent to employ methods which are not recursive if there is any possibility of exceeding available stack space.

/*------------------------------------------------
 SearchVol XFCN
 © 1989 MacTutor
 by Mark Armstrong    Pharos Technologies, Inc
 written in Think’s LightspeedC 3.0
------------------------------------------------*/

#include “HyperXCmd.h”
#include “FileMgr.h”
#include “HFS.h”
#include “ResourceMgr.h”
#include “SetUpA4.h”

#define False    0
#define True!False
#define Nil 0L

/*--------------------------------------
XFCN main function
--------------------------------------*/
pascal main(paramPtr)
   XCmdBlockPtr  paramPtr;
   {
   Str255 fName,str,fullPath,vName;
   HParamBlockRecMyHPB;
   CInfoPBRec    MyCIPB;
   OSErrfErr;
   shorttheVol;
   Handle nameH;
   long theDir,foundDir;
   
   RememberA0();
   SetUpA4();
   
   if ((paramPtr->paramCount < 1) || 
 (paramPtr->paramCount > 2)) 
   {
   SysBeep(10);
   /* return error string */
   goto Done;
   }
   
 ZeroToPas(paramPtr,*((unsigned char **)           paramPtr->params[0]), 
fName);
   if (paramPtr->paramCount == 2)
   {
   ZeroToPas(paramPtr,*((unsigned char **)               paramPtr->params[1]),vName);
   if (vName[vName[0]] != ‘:’)
   {
   vName[0]++;
   vName[vName[0]] = ‘:’;
   }
 MyHPB.volumeParam.ioCompletion = Nil;
 MyHPB.volumeParam.ioNamePtr = vName;
 MyHPB.volumeParam.ioVRefNum = 0;
 MyHPB.volumeParam.ioVolIndex = -1;
 fErr = PBHGetVInfo(&MyHPB,False);
 if (fErr)
 {
        SysBeep(10);
        /* return error string */
        goto Done;
 }
 theVol = MyHPB.volumeParam.ioVRefNum;
 }
   else theVol = GetSysVol();
   
   MyCIPB.dirInfo.ioCompletion = 0L;
   MyCIPB.dirInfo.ioNamePtr = 0L;
   MyCIPB.dirInfo.ioVRefNum = theVol;
   MyCIPB.dirInfo.ioFDirIndex = 0;
   MyCIPB.dirInfo.ioDrDirID = 2L;
   fErr = PBGetCatInfo(&MyCIPB,False);
   
   if (fErr)
 {
   SysBeep(10);
   /* return error string */
   goto Done;
 }
 else
   {
   fErr = 
 SearchFile(2L,
 MyCIPB.dirInfo.ioDrNmFls,
 theVol,
 &fName,
 &foundDir);
   if (fErr)
 {
   SysBeep(10);
   /* return error string */
   goto Done;
 }
 
   fullPath[0] = 0;
   PstrCopy(fullPath,fName);
   
   MyCIPB.dirInfo.ioCompletion = Nil;
   MyCIPB.dirInfo.ioNamePtr = str;
   MyCIPB.dirInfo.ioVRefNum = theVol;
   MyCIPB.dirInfo.ioFDirIndex = -1;
   MyCIPB.dirInfo.ioDrDirID = foundDir;
   fErr = PBGetCatInfo(&MyCIPB,False);
   PrependStr(MyCIPB.dirInfo.ioNamePtr,fullPath);
   
   do {
   MyCIPB.dirInfo.ioDrDirID =
 MyCIPB.dirInfo.ioDrParID;
   fErr = PBGetCatInfo(&MyCIPB,False);
   if (fErr == noErr)
 PrependStr(MyCIPB.dirInfo.ioNamePtr,fullPath);
   } while (fErr == noErr);
   
   paramPtr->returnValue =  PasToZero(paramPtr,(StringPtr)fullPath);
   }

Done:
   RestoreA4();
   }
  
/*--------------------------------------------
SearchFile is the recursive hierarchical search engine.  It looks at 
all the files and then all the folders in the directory specified by 
theVol and theDir for the file specified by fName
--------------------------------------------*/
SearchFile(theDir,count,theVol,fName,foundDir)
 long   theDir;
   shortcount,theVol;
   Str255 *fName;
   long *foundDir;
   {
   shortI;
   OSErrfErr;
   Str255 str;
   CInfoPBPtr    MyCIPB;
   
   MyCIPB = (CInfoPBPtr)NewPtr(sizeof(CInfoPBRec));
   for (I=1;I<=count;I++)
   {
   str[0] = 0;
   MyCIPB->dirInfo.ioCompletion = Nil;
   MyCIPB->dirInfo.ioNamePtr = str;
   MyCIPB->dirInfo.ioVRefNum = theVol;
   MyCIPB->dirInfo.ioFDirIndex = I;
   MyCIPB->dirInfo.ioDrDirID = theDir;
   fErr = PBGetCatInfo(MyCIPB,False);
   if (fErr) 
   {
   SysBeep(10);
   return (fErr);
   }
   else
   {
   if (!(MyCIPB->dirInfo.ioFlAttrib &  0x10))
   {
   if (EqualString(fName,
 MyCIPB->dirInfo.ioNamePtr,
 False,True))
   {
   *foundDir = 
 MyCIPB->hFileInfo.ioFlParID;
   return (0);
   }
   }
   }
   }
   
   for (I=1;I<=count;I++)
   {
   str[0] = 0;
   MyCIPB->dirInfo.ioCompletion = Nil;
   MyCIPB->dirInfo.ioNamePtr = str;
   MyCIPB->dirInfo.ioVRefNum = theVol;
   MyCIPB->dirInfo.ioFDirIndex = I;
   MyCIPB->dirInfo.ioDrDirID = theDir;
   fErr = PBGetCatInfo(MyCIPB,False);
   if (fErr) 
   {
   SysBeep(10);
   return (fErr);
   }
   else
   {
   if (MyCIPB->dirInfo.ioFlAttrib & 0x10)
   {
   fErr = 
 SearchFile(
 MyCIPB->dirInfo.ioDrDirID,
   MyCIPB->dirInfo.ioDrNmFls,
   theVol,
   fName,
   foundDir);
   if (!fErr) return (0);
   }
   }
   }
   
   DisposPtr(MyCIPB);
   return (fnfErr);
   }

/*--------------------------------------------
PrependStr puts string s1 and a colon before string s2.
--------------------------------------------*/
PrependStr(s1,s2)
 char   *s1,*s2;
 {
 Str255 temp;
 PstrCopy(temp,s2);
 s1[0]++;
 s1[s1[0]] = ‘:’;
 PstrCopy(s2,s1);
 BlockMove(&(temp[1]),&(s2[s2[0]+1]),
 (long)temp[0]);
 s2[0] += temp[0];
 }

/*--------------------------------------------
PstrCopy copies string s2 into string s1
--------------------------------------------*/
PstrCopy(s1,s2)
 char   *s1,*s2;
 {
 short  len;
 for (len=*s2;len>=0;--len) *s1++ = *s2++;
 }

/*--------------------------------------------
GetSysVol returns the vRefNum of the startup system volume.
--------------------------------------------*/
GetSysVol()
   {
   shortvRefNum;
   OSErrFErr;
   FErr = GetVRefNum(SysMap,&vRefNum);
   return vRefNum;
   }

[Mark Armstrong is presently the Vice President of Technical Operations for Pharos Technologies, Inc., a system integration and software development firm. He is the author of UNITize™, and has contributed to several other projects such as Milo™ and Marble Madness™.]

 
AAPL
$101.63
Apple Inc.
-0.03
MSFT
$46.24
Microsoft Corpora
-0.46
GOOG
$573.10
Google Inc.
-2.52

MacTech Search:
Community Search:

Software Updates via MacUpdate

NTFS 11.3.62 - Provides full read and wr...
Paragon NTFS breaks down the barriers between Windows and OS X. Paragon NTFS effectively solves the communication problems between the Mac system and NTFS, providing full read and write access to... Read more
OS X Yosemite 10.10 DP8 - Developer Prev...
Note: This is a Developer Preview. You must be a registered Apple Mac Developer to download this update. You can also sign up for the free OS X Beta Program to download and preview public beta... Read more
FotoMagico 4.5 - Powerful slideshow crea...
FotoMagico lets you create professional slideshows from your photos and music with just a few, simple mouse clicks. It sports a very clean and intuitive yet powerful user interface. High image... Read more
Screenshot Path 1.2.1 - Change the defau...
Screenshot Path lets you change the folder where OS X saves screenshots. Screenshots are saved by default to the user’s desktop. This is handy for the occasional screenshot but those looking to take... Read more
Fantastical 1.3.16 - Create calendar eve...
Fantastical is the Mac calendar you'll actually enjoy using. Creating an event with Fantastical is quick, easy, and fun: Open Fantastical with a single click or keystroke Type in your event details... Read more
GIMP 2.8.14 - Powerful, free image editi...
GIMP is a multi-platform photo manipulation tool. GIMP is an acronym for GNU Image Manipulation Program. The GIMP is suitable for a variety of image manipulation tasks, including photo retouching,... Read more
HoudahSpot 3.9.3 - Advanced front-end fo...
HoudahSpot is an advanced file search tool built upon MacOS X Spotlight. Spotlight unleashed Create detailed queries to locate the exact file you need Narrow down searches. Zero in on files Save... Read more
djay 4.2.3 - Transform your Mac into a f...
djay transforms your Mac into a full-fledged DJ system, allowing you to mix your iTunes music library on a hyper-realistic turntable interface. Perform live, record mixes on-the-go, or enable... Read more
iDefrag 2.2.8 - Disk defragmentation and...
iDefrag helps defragment and optimize your disk for improved performance. Features include: Supports HFS and HFS+ (Mac OS Extended). Supports case sensitive and journaled filesystems. Supports... Read more
Bookends 12.2.3 - Reference management a...
Bookends is a full-featured bibliography/reference and information-management system for students and professionals. Access the power of Bookends directly from Mellel, Nisus Writer Pro, or MS Word (... Read more

Latest Forum Discussions

See All

Vizzywig 4K (Photography)
Vizzywig 4K 1.0 Device: iOS iPhone Category: Photography Price: $999.99, Version: 1.0 (iTunes) Description: REQUIRES: iOS 7 on iPhone 5S with 32GB or 64GB. (Do not use iOS 8)The world's FIRST mobile 4K video capture, editing and... | Read more »
The Sleeping Prince Review
The Sleeping Prince Review By Jennifer Allen on September 15th, 2014 Our Rating: :: RESTRICTIVE KINGDOM SAVINGUniversal App - Designed for iPhone and iPad The Sleeping Prince looks and feels great to play, but its lack of peril and... | Read more »
It Came From Canada: Terra Battle
In some way or another, most Japanese RPGs owe something to Final Fantasy. But with Terra Battle, the now-common mix of Western medieval fantasy with Eastern anime aesthetic feels earned. After all, its developer, Mistwalker, was founded by the... | Read more »
Five Nights at Freddy’s Review
Five Nights at Freddy’s Review By Rob Thomas on September 15th, 2014 Our Rating: :: FIVE FRIGHTS AT FREDDY'SUniversal App - Designed for iPhone and iPad Can you survive five nights as the new night watchman of Freddy Fazbear’s... | Read more »
Phantom Rift Review
Phantom Rift Review By Nadia Oxford on September 15th, 2014 Our Rating: :: FRIENDLY PHANTOMUniversal App - Designed for iPhone and iPad Despite a snag here and there, Phantom Rift is a well-crafted and imaginative adventure RPG.   | Read more »
Phantom Rift – Tips, Tricks, Strategies,...
Hello, Wanderers: | Read more »
Meet the Newest Character for Temple Run...
Meet the Newest Character for Temple Run 2, from National Geographic Kids’ Action-Adventure Book Posted by Jessica Fisher on September 15th, 2014 [ | Read more »
Battle Riders Review
Battle Riders Review By Jordan Minor on September 15th, 2014 Our Rating: :: UNTWISTED METALUniversal App - Designed for iPhone and iPad BattleRiders has cool car combat, but it could be crazier.   | Read more »
Rapture - World Conquest (Games)
Rapture - World Conquest 1.0.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0.0 (iTunes) Description: The End is coming! Bombard the globe with devastating miracles and decimate the enemy civilizations. Guide your... | Read more »
TRANSFORMERS: Age of Extinction Update A...
TRANSFORMERS: Age of Extinction Update Adds New Levels, a New Boss, and Special Events Posted by Jessica Fisher on September 15th, 2014 [ p | Read more »

Price Scanner via MacPrices.net

Free GIMP Professional Grade Graphics App Ver...
The latest 2.8.14 version of the oddly-named GIMP (acronym for: GNU Image Manipulation Program) open source, high-end image editing and creation alternative to Adobe’s Photoshop and refuge from... Read more
10% off iPhone 6 and 6 Plus Otterbox cases
Get 10% off on popular Otterbox iPhone 6 and iPhone 6 Plus cases at MacMall through September 19th. Use code OTTERBOX10 to see the discount. Read more
15-inch MacBook Pros on sale for up to $125 o...
Amazon has the new 2014 15″ Retina MacBook Pros on sale for up to $125 off MSRP including free shipping: - 15″ 2.2GHz Retina MacBook Pro: $1899.99 save $100 - 15″ 2.5GHz Retina MacBook Pro: $2374... Read more
27-inch 3.2GHz iMac on sale for $1698, $101 o...
Abt has the 27″ 3.2GHz iMac on sale for $1698 including free shipping. Their price is $101 off MSRP. Read more
More To Making A Larger iPad Than Expanded Sc...
CNET’s Ross Rubin has posted a thoughtful analysis of prospects for a larger display iPad Pro, noting that Microsoft and Samsung currently have the large-display touchscreen tablet category to... Read more
SwiftKey Keyboard Finally Coming To iPhone An...
At the TechCrunch Disrupt event in San Francisco, Swiftkey unveiled the first details about SwiftKey Keyboard for iPhone, iPad & iPod touch. SwiftKey’s philosophy is that you should be able to... Read more
Save $75 on the 16GB iPad mini with Retina Di...
Best Buy has the 16GB iPad mini with Retina Display on sale for $324.99 on their online store for a limited time. Their price is $75 off MSRP, and it’s the lowest price available for this mini.... Read more
21-inch 1.4GHz iMac on sale for $979, $120 of...
B&H Photo has the new 21″ 1.4GHz iMac on sale for $979.99 including free shipping plus NY sales tax only. Their price is $120 off MSRP. B&H will also include free copies of Parallels Desktop... Read more
Apple restocks refurbished 21-inch 1.4GHz iMa...
The Apple Store has restocked Apple Certified Refurbished 21″ 1.4GHz iMacs for $929 including free shipping plus Apple’s standard one-year warranty. Their price is $170 off the cost of new models,... Read more
13-inch 2.6GHz/256GB Retina MacBook Pro on sa...
Adorama has the 13″ 2.6GHz/256GB Retina MacBook Pro on sale for $1379 including free shipping plus NY & NJ sales tax only. Their price is $120 off MSRP, and it’s the lowest price available for... Read more

Jobs Board

*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.