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™.]

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

calibre 3.1.1 - Complete e-book library...
Calibre is a complete e-book library manager. Organize your collection, convert your books to multiple formats, and sync with all of your devices. Let Calibre be your multi-tasking digital librarian... Read more
Sparkle Pro 2.2 - $79.99
Sparkle Pro will change your mind if you thought building websites wasn't for you. Sparkle is the intuitive site builder that lets you create sites for your online portfolio, team or band pages, or... Read more
Spotify 1.0.57.474. - Stream music, crea...
Spotify is a streaming music service that gives you on-demand access to millions of songs. Whether you like driving rock, silky R&B, or grandiose classical music, Spotify's massive catalogue puts... Read more
beaTunes 5.0.1 - Organize your music col...
beaTunes is a full-featured music player and organizational tool for music collections. How well organized is your music library? Are your artists always spelled the same way? Any R.E.M. vs REM?... Read more
LibreOffice 5.3.4.2 - Free, open-source...
LibreOffice is an office suite (word processor, spreadsheet, presentations, drawing tool) compatible with other major office suites. The Document Foundation is coordinating development and... Read more
VOX 2.8.26 - Music player that supports...
VOX just sounds better! The beauty is in its simplicity, yet behind the minimal exterior lies a powerful music player with a ton of features and support for all audio formats you should ever need.... Read more
iFFmpeg 6.4.0 - Convert multimedia files...
iFFmpeg is a comprehensive media tool to convert movie, audio and media files between formats. The FFmpeg command line instructions can be very hard to master/understand, so iFFmpeg does all the hard... Read more
Beamer 3.3 - Stream any movie file from...
Beamer streams to your Apple TV.... Plays any movie file - Just like the popular desktop movie players, Beamer accepts all common formats, codecs and resolutions. AVI, MKV, MOV, MP4, WMV, FLV. To... Read more
jAlbum Pro 14.0 - Organize your digital...
jAlbum Pro has all the features you love in jAlbum, but comes with a commercial license. You can create gorgeous custom photo galleries for the Web without writing a line of code! Beginner-friendly... Read more
Apple Remote Desktop Client 3.9.3 - Clie...
Apple Remote Desktop Client is the best way to manage the Mac computers on your network. Distribute software, provide real-time online help to end users, create detailed software and hardware reports... Read more

Latest Forum Discussions

See All

This War of Mine gets a new ending and m...
This War of Mine just got a big new update, featuring free DLC that adds a new ending to the game, among other exciting changes. The update is celebrating the game's two-year release anniversary. Apart from the new ending, which will be quite... | Read more »
Summon eight new heroes in Fire Emblem H...
Nintendo keeps coming at us with Fire Emblem Heroes updates, and it doesn't look like that trend is stopping anytime soon. The folks behind the game have just announced the new War of the Clerics Voting Gauntlet, expected to start next Tuesday. [... | Read more »
The best deals on the App Store this wee...
iOS publishers are pulling out all the stops this week -- there's a huge number of seriously great games at discounted prices this week. Let's not waste any time and get right down to business. [Read more] | Read more »
The House of da Vinci (Games)
The House of da Vinci 1.0.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0.0 (iTunes) Description: Enter The House of Da Vinci, a new must-try 3D puzzle adventure game. Solve mechanical puzzles, discover hidden... | Read more »
Solve the disappearance of history’s gre...
Blue Brain Games invites you to indulge in an immersive hands-on 3D puzzle adventure in similar vein to The Room series, with its debut release The House of Da Vinci. Set during the historic period of the Italian Renaissance (when Leonardo himself... | Read more »
Age of Rivals (Games)
Age of Rivals 3.3 Device: iOS Universal Category: Games Price: $.99, Version: 3.3 (iTunes) Description: Deep civilization-building strategy in a fast-paced card game! | Read more »
Panthera Frontier (Games)
Panthera Frontier 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: | Read more »
Angry Birds Evolution beginner's gu...
Angry Birds changes things up a fair bit in its latest iteration, Angry Birds Evolution. The familiar sling-shot physics mechanics are still there, but the game now features team-based gameplay, RPG elements, and a new top-down view. With all of... | Read more »
Sega Forever is for the retro game fans
Sega is launching a new retro games service titled Sega Forever, in a move that's sure to delight games enthusiasts with a bit of nostalgia. Sega's releasing five classic games for free. The titles include Sonic the Hedgehog, Phantasy Star II,... | Read more »
The Little Acre (Games)
The Little Acre 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: | Read more »

Price Scanner via MacPrices.net

ABBYY TextGrabber 6 for iOS Implements Instan...
ABBYY has announced the release of TextGrabber 6.0.0, an important feature update to the company’s productivity app developed for iOS and Android devices. TextGrabber 6.0 now offers Real-Time... Read more
vPhone, First Smartphone That Can’t Be Lost,...
Austin, Texas based Hypori has introduced the vPhone, a virtual smartphone that affords every business user the benefits of separate work and personal phones, conveniently delivered on a single... Read more
Save this weekend with 2016 refurbished MacBo...
Apple has dropped prices on Certified Refurbished 2016 15″ and 13″ MacBook Pros by as much as $590 off original MSRP. An Apple one-year warranty is included with each model, and shipping is free: -... Read more
New 27-inch 3.4GHz iMac on sale for $1699, sa...
MacMall has the new 2017 27″ 3.4GHz iMac (MNE92LL/A) in stock and on sale for $1699 including free shipping. Their price is $100 off MSRP. Read more
Clearance 2016 MacBook Pros available for up...
B&H Photo has clearance 2016 13″ and 15″ MacBook Pros in stock today and on sale for up to $400 off original MSRP. Shipping is free, and B&H charges NY & NJ sales tax only: - 15″ 2.7GHz... Read more
Apple Ranks 9th In comScore Top 50 U.S. Digit...
comScore, Inc. has released its monthly ranking of U.S. online activity at the top digital media properties for May 2017 based on data from comScore Media Metrix Multi-Platform. * Entity has... Read more
10.5-inch iPad Pros available for up to $20 o...
B&H Photo has the new 2017 10.5″ iPad Pros available for up to $20 off MSRP including free shipping plus NY & NJ sales tax only: - 64GB iPad Pro WiFi: $649 - 256GB iPad Pro WiFi: $749 - 512GB... Read more
Three Off-The-Beaten-Track iOS Apps That Dese...
One of the great things about using iPads and iPhones is the vast selection of apps available for most anything you want or need to do. The three outlined in this article have been in my core app... Read more
Apple No. 1 Spot In Gartner Top 100 Vendors i...
Gartner, Inc. has unveiled the top global 100 vendors in IT in 2016 based on their revenue across IT (excluding communication services) and component market segments. In the Gartner Global Top 100:... Read more
Clearance iMacs available for up to $300 off...
B&H Photo has clearance 21″ and 27″ Apple iMacs available starting at $949, each including free shipping plus NY & NJ sales tax only: - 27″ 3.3GHz iMac 5K: $1999 $300 off original MSRP - 27″... Read more

Jobs Board

*Apple* Retail - Multiple Positions - Apple,...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
Security Data Analyst - *Apple* Information...
…data sources need to be collected to allow Information Security to better protect Apple employees and customers from a wide range of threats.Act as the subject matter Read more
Lead *Apple* Solutions Consultant - Apple I...
…integrity, and trust.Success Metrics/Key Performance Indicators:Quantitative* Year over Year growth in Apple Product and Beyond the Box sales in the assigned Point of Read more
*Apple* Solutions Consultant till v%u00E5r...
…ethics, integrity, and trust.Success Metrics/Key Performance Indicators:QuantitativeYear over Year growth in Apple Product and Beyond the Box sales in the assigned Point Read more
Sr. Software Engineer, *Apple* Retail - App...
Apple Retail is looking for a Software Engineer…You'll work on projects that touch all aspects of Apple Retail Point-of-Sale system, and will leverage your strong Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.